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<img alt="Erlang logo" src="../../../../doc/erlang-logo.png"><br><small><a href="index.html">Reference Manual</a><br><a href="release_notes.html">Release Notes</a><br><a href="../pdf/kernel-2.13.5.pdf">PDF</a><br><a href="../../../../doc/index.html">Top</a></small><p><strong>Kernel</strong><br><strong>Reference Manual</strong><br><small>Version 2.13.5</small></p>
<br><a href="javascript:openAllFlips()">Expand All</a><br><a href="javascript:closeAllFlips()">Contract All</a><p><small><strong>Table of Contents</strong></small></p>
<ul class="flipMenu">
<li title="kernel (App)"><a href="kernel_app.html">kernel (App)
</a></li>
<li id="no" title="application " expanded="false">application<ul>
<li><a href="application.html">
Top of manual page
</a></li>
<li title="get_all_env-0"><a href="application.html#get_all_env-0">get_all_env/0</a></li>
<li title="get_all_env-1"><a href="application.html#get_all_env-1">get_all_env/1</a></li>
<li title="get_all_key-0"><a href="application.html#get_all_key-0">get_all_key/0</a></li>
<li title="get_all_key-1"><a href="application.html#get_all_key-1">get_all_key/1</a></li>
<li title="get_application-0"><a href="application.html#get_application-0">get_application/0</a></li>
<li title="get_application-1"><a href="application.html#get_application-1">get_application/1</a></li>
<li title="get_env-1"><a href="application.html#get_env-1">get_env/1</a></li>
<li title="get_env-2"><a href="application.html#get_env-2">get_env/2</a></li>
<li title="get_key-1"><a href="application.html#get_key-1">get_key/1</a></li>
<li title="get_key-2"><a href="application.html#get_key-2">get_key/2</a></li>
<li title="load-1"><a href="application.html#load-1">load/1</a></li>
<li title="load-2"><a href="application.html#load-2">load/2</a></li>
<li title="loaded_applications-0"><a href="application.html#loaded_applications-0">loaded_applications/0</a></li>
<li title="permit-2"><a href="application.html#permit-2">permit/2</a></li>
<li title="set_env-3"><a href="application.html#set_env-3">set_env/3</a></li>
<li title="set_env-4"><a href="application.html#set_env-4">set_env/4</a></li>
<li title="start-1"><a href="application.html#start-1">start/1</a></li>
<li title="start-2"><a href="application.html#start-2">start/2</a></li>
<li title="start_type-0"><a href="application.html#start_type-0">start_type/0</a></li>
<li title="stop-1"><a href="application.html#stop-1">stop/1</a></li>
<li title="takeover-2"><a href="application.html#takeover-2">takeover/2</a></li>
<li title="unload-1"><a href="application.html#unload-1">unload/1</a></li>
<li title="unset_env-2"><a href="application.html#unset_env-2">unset_env/2</a></li>
<li title="unset_env-3"><a href="application.html#unset_env-3">unset_env/3</a></li>
<li title="which_applications-0"><a href="application.html#which_applications-0">which_applications/0</a></li>
<li title="which_applications-1"><a href="application.html#which_applications-1">which_applications/1</a></li>
<li title="Module:start-2"><a href="application.html#Module:start-2">Module:start/2</a></li>
<li title="Module:start_phase-3"><a href="application.html#Module:start_phase-3">Module:start_phase/3</a></li>
<li title="Module:prep_stop-1"><a href="application.html#Module:prep_stop-1">Module:prep_stop/1</a></li>
<li title="Module:stop-1"><a href="application.html#Module:stop-1">Module:stop/1</a></li>
<li title="Module:config_change-3"><a href="application.html#Module:config_change-3">Module:config_change/3</a></li>
</ul>
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<li id="no" title="auth " expanded="false">auth<ul>
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<li title="is_auth-1"><a href="auth.html#is_auth-1">is_auth/1</a></li>
<li title="cookie-0"><a href="auth.html#cookie-0">cookie/0</a></li>
<li title="cookie-1"><a href="auth.html#cookie-1">cookie/1</a></li>
<li title="node_cookie-1"><a href="auth.html#node_cookie-1">node_cookie/1</a></li>
<li title="node_cookie-2"><a href="auth.html#node_cookie-2">node_cookie/2</a></li>
</ul>
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<li id="no" title="code " expanded="false">code<ul>
<li><a href="code.html">
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</a></li>
<li title="set_path-1"><a href="code.html#set_path-1">set_path/1</a></li>
<li title="get_path-0"><a href="code.html#get_path-0">get_path/0</a></li>
<li title="add_path-1"><a href="code.html#add_path-1">add_path/1</a></li>
<li title="add_pathz-1"><a href="code.html#add_pathz-1">add_pathz/1</a></li>
<li title="add_patha-1"><a href="code.html#add_patha-1">add_patha/1</a></li>
<li title="add_paths-1"><a href="code.html#add_paths-1">add_paths/1</a></li>
<li title="add_pathsz-1"><a href="code.html#add_pathsz-1">add_pathsz/1</a></li>
<li title="add_pathsa-1"><a href="code.html#add_pathsa-1">add_pathsa/1</a></li>
<li title="del_path-1"><a href="code.html#del_path-1">del_path/1</a></li>
<li title="replace_path-2"><a href="code.html#replace_path-2">replace_path/2</a></li>
<li title="load_file-1"><a href="code.html#load_file-1">load_file/1</a></li>
<li title="load_abs-1"><a href="code.html#load_abs-1">load_abs/1</a></li>
<li title="ensure_loaded-1"><a href="code.html#ensure_loaded-1">ensure_loaded/1</a></li>
<li title="load_binary-3"><a href="code.html#load_binary-3">load_binary/3</a></li>
<li title="delete-1"><a href="code.html#delete-1">delete/1</a></li>
<li title="purge-1"><a href="code.html#purge-1">purge/1</a></li>
<li title="soft_purge-1"><a href="code.html#soft_purge-1">soft_purge/1</a></li>
<li title="is_loaded-1"><a href="code.html#is_loaded-1">is_loaded/1</a></li>
<li title="all_loaded-0"><a href="code.html#all_loaded-0">all_loaded/0</a></li>
<li title="which-1"><a href="code.html#which-1">which/1</a></li>
<li title="get_object_code-1"><a href="code.html#get_object_code-1">get_object_code/1</a></li>
<li title="root_dir-0"><a href="code.html#root_dir-0">root_dir/0</a></li>
<li title="lib_dir-0"><a href="code.html#lib_dir-0">lib_dir/0</a></li>
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<li title="lib_dir-2"><a href="code.html#lib_dir-2">lib_dir/2</a></li>
<li title="compiler_dir-0"><a href="code.html#compiler_dir-0">compiler_dir/0</a></li>
<li title="priv_dir-1"><a href="code.html#priv_dir-1">priv_dir/1</a></li>
<li title="objfile_extension-0"><a href="code.html#objfile_extension-0">objfile_extension/0</a></li>
<li title="stick_dir-1"><a href="code.html#stick_dir-1">stick_dir/1</a></li>
<li title="unstick_dir-1"><a href="code.html#unstick_dir-1">unstick_dir/1</a></li>
<li title="is_sticky-1"><a href="code.html#is_sticky-1">is_sticky/1</a></li>
<li title="rehash-0"><a href="code.html#rehash-0">rehash/0</a></li>
<li title="where_is_file-1"><a href="code.html#where_is_file-1">where_is_file/1</a></li>
<li title="clash-0"><a href="code.html#clash-0">clash/0</a></li>
<li title="is_module_native-1"><a href="code.html#is_module_native-1">is_module_native/1</a></li>
</ul>
</li>
<li id="no" title="disk_log " expanded="false">disk_log<ul>
<li><a href="disk_log.html">
Top of manual page
</a></li>
<li title="accessible_logs-0"><a href="disk_log.html#accessible_logs-0">accessible_logs/0</a></li>
<li title="alog-2"><a href="disk_log.html#alog-2">alog/2</a></li>
<li title="balog-2"><a href="disk_log.html#balog-2">balog/2</a></li>
<li title="alog_terms-2"><a href="disk_log.html#alog_terms-2">alog_terms/2</a></li>
<li title="balog_terms-2"><a href="disk_log.html#balog_terms-2">balog_terms/2</a></li>
<li title="block-1"><a href="disk_log.html#block-1">block/1</a></li>
<li title="block-2"><a href="disk_log.html#block-2">block/2</a></li>
<li title="change_header-2"><a href="disk_log.html#change_header-2">change_header/2</a></li>
<li title="change_notify-3"><a href="disk_log.html#change_notify-3">change_notify/3</a></li>
<li title="change_size-2"><a href="disk_log.html#change_size-2">change_size/2</a></li>
<li title="chunk-2"><a href="disk_log.html#chunk-2">chunk/2</a></li>
<li title="chunk-3"><a href="disk_log.html#chunk-3">chunk/3</a></li>
<li title="bchunk-2"><a href="disk_log.html#bchunk-2">bchunk/2</a></li>
<li title="bchunk-3"><a href="disk_log.html#bchunk-3">bchunk/3</a></li>
<li title="chunk_info-1"><a href="disk_log.html#chunk_info-1">chunk_info/1</a></li>
<li title="chunk_step-3"><a href="disk_log.html#chunk_step-3">chunk_step/3</a></li>
<li title="close-1"><a href="disk_log.html#close-1">close/1</a></li>
<li title="format_error-1"><a href="disk_log.html#format_error-1">format_error/1</a></li>
<li title="inc_wrap_file-1"><a href="disk_log.html#inc_wrap_file-1">inc_wrap_file/1</a></li>
<li title="info-1"><a href="disk_log.html#info-1">info/1</a></li>
<li title="lclose-1"><a href="disk_log.html#lclose-1">lclose/1</a></li>
<li title="lclose-2"><a href="disk_log.html#lclose-2">lclose/2</a></li>
<li title="log-2"><a href="disk_log.html#log-2">log/2</a></li>
<li title="blog-2"><a href="disk_log.html#blog-2">blog/2</a></li>
<li title="log_terms-2"><a href="disk_log.html#log_terms-2">log_terms/2</a></li>
<li title="blog_terms-2"><a href="disk_log.html#blog_terms-2">blog_terms/2</a></li>
<li title="open-1"><a href="disk_log.html#open-1">open/1</a></li>
<li title="pid2name-1"><a href="disk_log.html#pid2name-1">pid2name/1</a></li>
<li title="reopen-2"><a href="disk_log.html#reopen-2">reopen/2</a></li>
<li title="reopen-3"><a href="disk_log.html#reopen-3">reopen/3</a></li>
<li title="breopen-3"><a href="disk_log.html#breopen-3">breopen/3</a></li>
<li title="sync-1"><a href="disk_log.html#sync-1">sync/1</a></li>
<li title="truncate-1"><a href="disk_log.html#truncate-1">truncate/1</a></li>
<li title="truncate-2"><a href="disk_log.html#truncate-2">truncate/2</a></li>
<li title="btruncate-2"><a href="disk_log.html#btruncate-2">btruncate/2</a></li>
<li title="unblock-1"><a href="disk_log.html#unblock-1">unblock/1</a></li>
</ul>
</li>
<li id="no" title="erl_boot_server " expanded="false">erl_boot_server<ul>
<li><a href="erl_boot_server.html">
Top of manual page
</a></li>
<li title="start-1"><a href="erl_boot_server.html#start-1">start/1</a></li>
<li title="start_link-1"><a href="erl_boot_server.html#start_link-1">start_link/1</a></li>
<li title="add_slave-1"><a href="erl_boot_server.html#add_slave-1">add_slave/1</a></li>
<li title="delete_slave-1"><a href="erl_boot_server.html#delete_slave-1">delete_slave/1</a></li>
<li title="which_slaves-0"><a href="erl_boot_server.html#which_slaves-0">which_slaves/0</a></li>
</ul>
</li>
<li id="no" title="erl_ddll " expanded="false">erl_ddll<ul>
<li><a href="erl_ddll.html">
Top of manual page
</a></li>
<li title="demonitor-1"><a href="erl_ddll.html#demonitor-1">demonitor/1</a></li>
<li title="info-0"><a href="erl_ddll.html#info-0">info/0</a></li>
<li title="info-1"><a href="erl_ddll.html#info-1">info/1</a></li>
<li title="info-2"><a href="erl_ddll.html#info-2">info/2</a></li>
<li title="load-2"><a href="erl_ddll.html#load-2">load/2</a></li>
<li title="load_driver-2"><a href="erl_ddll.html#load_driver-2">load_driver/2</a></li>
<li title="monitor-2"><a href="erl_ddll.html#monitor-2">monitor/2</a></li>
<li title="reload-2"><a href="erl_ddll.html#reload-2">reload/2</a></li>
<li title="reload_driver-2"><a href="erl_ddll.html#reload_driver-2">reload_driver/2</a></li>
<li title="try_load-3"><a href="erl_ddll.html#try_load-3">try_load/3</a></li>
<li title="try_unload-2"><a href="erl_ddll.html#try_unload-2">try_unload/2</a></li>
<li title="unload-1"><a href="erl_ddll.html#unload-1">unload/1</a></li>
<li title="unload_driver-1"><a href="erl_ddll.html#unload_driver-1">unload_driver/1</a></li>
<li title="loaded_drivers-0"><a href="erl_ddll.html#loaded_drivers-0">loaded_drivers/0</a></li>
<li title="format_error-1"><a href="erl_ddll.html#format_error-1">format_error/1</a></li>
</ul>
</li>
<li title="erl_prim_loader"><a href="erl_prim_loader.html">erl_prim_loader</a></li>
<li title="erlang"><a href="erlang.html">erlang</a></li>
<li id="no" title="error_handler " expanded="false">error_handler<ul>
<li><a href="error_handler.html">
Top of manual page
</a></li>
<li title="undefined_function-3"><a href="error_handler.html#undefined_function-3">undefined_function/3</a></li>
<li title="undefined_lambda-3"><a href="error_handler.html#undefined_lambda-3">undefined_lambda/3</a></li>
</ul>
</li>
<li id="no" title="error_logger " expanded="false">error_logger<ul>
<li><a href="error_logger.html">
Top of manual page
</a></li>
<li title="error_msg-1"><a href="error_logger.html#error_msg-1">error_msg/1</a></li>
<li title="error_msg-2"><a href="error_logger.html#error_msg-2">error_msg/2</a></li>
<li title="format-2"><a href="error_logger.html#format-2">format/2</a></li>
<li title="error_report-1"><a href="error_logger.html#error_report-1">error_report/1</a></li>
<li title="error_report-2"><a href="error_logger.html#error_report-2">error_report/2</a></li>
<li title="warning_map-0"><a href="error_logger.html#warning_map-0">warning_map/0</a></li>
<li title="warning_msg-1"><a href="error_logger.html#warning_msg-1">warning_msg/1</a></li>
<li title="warning_msg-2"><a href="error_logger.html#warning_msg-2">warning_msg/2</a></li>
<li title="warning_report-1"><a href="error_logger.html#warning_report-1">warning_report/1</a></li>
<li title="warning_report-2"><a href="error_logger.html#warning_report-2">warning_report/2</a></li>
<li title="info_msg-1"><a href="error_logger.html#info_msg-1">info_msg/1</a></li>
<li title="info_msg-2"><a href="error_logger.html#info_msg-2">info_msg/2</a></li>
<li title="info_report-1"><a href="error_logger.html#info_report-1">info_report/1</a></li>
<li title="info_report-2"><a href="error_logger.html#info_report-2">info_report/2</a></li>
<li title="add_report_handler-1"><a href="error_logger.html#add_report_handler-1">add_report_handler/1</a></li>
<li title="add_report_handler-2"><a href="error_logger.html#add_report_handler-2">add_report_handler/2</a></li>
<li title="delete_report_handler-1"><a href="error_logger.html#delete_report_handler-1">delete_report_handler/1</a></li>
<li title="tty-1"><a href="error_logger.html#tty-1">tty/1</a></li>
<li title="logfile-1"><a href="error_logger.html#logfile-1">logfile/1</a></li>
</ul>
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<li id="loadscrollpos" title="file " expanded="true">file<ul>
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<li title="change_group-2"><a href="file.html#change_group-2">change_group/2</a></li>
<li title="change_owner-2"><a href="file.html#change_owner-2">change_owner/2</a></li>
<li title="change_owner-3"><a href="file.html#change_owner-3">change_owner/3</a></li>
<li title="change_time-2"><a href="file.html#change_time-2">change_time/2</a></li>
<li title="change_time-3"><a href="file.html#change_time-3">change_time/3</a></li>
<li title="close-1"><a href="file.html#close-1">close/1</a></li>
<li title="consult-1"><a href="file.html#consult-1">consult/1</a></li>
<li title="copy-2"><a href="file.html#copy-2">copy/2</a></li>
<li title="copy-3"><a href="file.html#copy-3">copy/3</a></li>
<li title="del_dir-1"><a href="file.html#del_dir-1">del_dir/1</a></li>
<li title="delete-1"><a href="file.html#delete-1">delete/1</a></li>
<li title="eval-1"><a href="file.html#eval-1">eval/1</a></li>
<li title="eval-2"><a href="file.html#eval-2">eval/2</a></li>
<li title="file_info-1"><a href="file.html#file_info-1">file_info/1</a></li>
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<li title="make_dir-1"><a href="file.html#make_dir-1">make_dir/1</a></li>
<li title="make_link-2"><a href="file.html#make_link-2">make_link/2</a></li>
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<li title="open-2"><a href="file.html#open-2">open/2</a></li>
<li title="path_consult-2"><a href="file.html#path_consult-2">path_consult/2</a></li>
<li title="path_eval-2"><a href="file.html#path_eval-2">path_eval/2</a></li>
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<div id="content">
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<!-- refpage --><center><h1>file</h1></center>
<h3>MODULE</h3>
<div class="REFBODY">file</div>
<h3>MODULE SUMMARY</h3>
<div class="REFBODY">File Interface Module</div>
<h3>DESCRIPTION</h3>
<div class="REFBODY"><p>
<p>The module <span class="code">file</span> provides an interface to the file system.</p>
<p>On operating systems with thread support, it is possible to let
file operations be performed in threads of their own, allowing
other Erlang processes to continue executing in parallel with
the file operations. See the command line flag
<span class="code">+A</span> in <span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','erts','erl.html');">erl(1)</a></span>.</p>
</p></div>
<h3><a name="id2312493">DATA TYPES</a></h3>
<div class="REFBODY">
<div class="example"><pre>
iodata() = iolist() | binary()
iolist() = [char() | binary() | iolist()]
io_device()
as returned by file:open/2, a process handling IO protocols
name() = string() | atom() | DeepList
DeepList = [char() | atom() | DeepList]
posix()
an atom which is named from the POSIX error codes used in
Unix, and in the runtime libraries of most C compilers
ext_posix() = posix() | badarg
time() = {{Year, Month, Day}, {Hour, Minute, Second}}
Year = Month = Day = Hour = Minute = Second = int()
Must denote a valid date and time</pre></div>
</div>
<h3>EXPORTS</h3>
<p><a name="change_group-2"><span class="bold_code">change_group(Filename, Gid) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Gid = int()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Changes group of a file. See
<span class="bold_code"><a href="#write_file_info-2">write_file_info/2</a></span>.</p>
</p></div>
<p><a name="change_owner-2"><span class="bold_code">change_owner(Filename, Uid) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Uid = int()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Changes owner of a file. See
<span class="bold_code"><a href="#write_file_info-2">write_file_info/2</a></span>.</p>
</p></div>
<p><a name="change_owner-3"><span class="bold_code">change_owner(Filename, Uid, Gid) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Uid = int()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Gid = int()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Changes owner and group of a file. See
<span class="bold_code"><a href="#write_file_info-2">write_file_info/2</a></span>.</p>
</p></div>
<p><a name="change_time-2"><span class="bold_code">change_time(Filename, Mtime) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Mtime = time()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Changes the modification and access times of a file. See
<span class="bold_code"><a href="#write_file_info-2">write_file_info/2</a></span>.</p>
</p></div>
<p><a name="change_time-3"><span class="bold_code">change_time(Filename, Mtime, Atime) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Mtime = Atime = time()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Changes the modification and last access times of a file. See
<span class="bold_code"><a href="#write_file_info-2">write_file_info/2</a></span>.</p>
</p></div>
<p><a name="close-1"><span class="bold_code">close(IoDevice) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">IoDevice = io_device()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Closes the file referenced by <span class="code">IoDevice</span>. It mostly
returns <span class="code">ok</span>, expect for some severe errors such as out
of memory.</p>
<p>Note that if the option <span class="code">delayed_write</span> was
used when opening the file, <span class="code">close/1</span> might return an
old write error and not even try to close the file. See
<span class="bold_code"><a href="#open-2">open/2</a></span>.</p>
</p></div>
<p><a name="consult-1"><span class="bold_code">consult(Filename) -> {ok, Terms} | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Terms = [term()]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated | system_limit
| {Line, Mod, Term}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Line, Mod, Term -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Reads Erlang terms, separated by '.', from <span class="code">Filename</span>.
Returns one of the following:</p>
<dl>
<dt><strong><span class="code">{ok, Terms}</span></strong></dt>
<dd>
<p>The file was successfully read.</p>
</dd>
<dt><strong><span class="code">{error, atom()}</span></strong></dt>
<dd>
<p>An error occurred when opening the file or reading it.
See <span class="bold_code"><a href="#open-2">open/2</a></span> for a list
of typical error codes.</p>
</dd>
<dt><strong><span class="code">{error, {Line, Mod, Term}}</span></strong></dt>
<dd>
<p>An error occurred when interpreting the Erlang terms in
the file. Use <span class="code">format_error/1</span> to convert
the three-element tuple to an English description of
the error.</p>
</dd>
</dl>
<p>Example:</p>
<div class="example"><pre>
f.txt: {person, "kalle", 25}.
{person, "pelle", 30}.</pre></div>
<div class="example"><pre>
1> <span class="bold_code">file:consult("f.txt").</span>
{ok,[{person,"kalle",25},{person,"pelle",30}]}</pre></div>
</p></div>
<p><a name="copy-2"><span class="bold_code">copy(Source, Destination) -></span></a><br><a name="copy-3"><span class="bold_code">copy(Source, Destination, ByteCount) -> {ok, BytesCopied} | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Source = Destination = io_device() | Filename | {Filename, Modes}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Modes = [Mode] -- see open/2</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">ByteCount = int() >= 0 | infinity</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">BytesCopied = int()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Copies <span class="code">ByteCount</span> bytes from <span class="code">Source</span> to
<span class="code">Destination</span>. <span class="code">Source</span> and <span class="code">Destination</span> refer
to either filenames or IO devices from e.g. <span class="code">open/2</span>.
<span class="code">ByteCount</span> defaults <span class="code">infinity</span>, denoting an
infinite number of bytes.</p>
<p>The argument <span class="code">Modes</span> is a list of possible modes, see
<span class="bold_code"><a href="#open-2">open/2</a></span>, and defaults to
[].</p>
<p>If both <span class="code">Source</span> and <span class="code">Destination</span> refer to
filenames, the files are opened with <span class="code">[read, binary]</span>
and <span class="code">[write, binary]</span> prepended to their mode lists,
respectively, to optimize the copy.</p>
<p>If <span class="code">Source</span> refers to a filename, it is opened with
<span class="code">read</span> mode prepended to the mode list before the copy,
and closed when done.</p>
<p>If <span class="code">Destination</span> refers to a filename, it is opened
with <span class="code">write</span> mode prepended to the mode list before
the copy, and closed when done.</p>
<p>Returns <span class="code">{ok, BytesCopied}</span> where <span class="code">BytesCopied</span> is
the number of bytes that actually was copied, which may be
less than <span class="code">ByteCount</span> if end of file was encountered on
the source. If the operation fails, <span class="code">{error, Reason}</span> is
returned.</p>
<p>Typical error reasons: As for <span class="code">open/2</span> if a file had to
be opened, and as for <span class="code">read/2</span> and <span class="code">write/2</span>.</p>
</p></div>
<p><a name="del_dir-1"><span class="bold_code">del_dir(Dir) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Dir = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Tries to delete the directory <span class="code">Dir</span>. The directory must
be empty before it can be deleted. Returns <span class="code">ok</span> if
successful.</p>
<p>Typical error reasons are:</p>
<dl>
<dt><strong><span class="code">eacces</span></strong></dt>
<dd>
<p>Missing search or write permissions for the parent
directories of <span class="code">Dir</span>.</p>
</dd>
<dt><strong><span class="code">eexist</span></strong></dt>
<dd>
<p>The directory is not empty.</p>
</dd>
<dt><strong><span class="code">enoent</span></strong></dt>
<dd>
<p>The directory does not exist.</p>
</dd>
<dt><strong><span class="code">enotdir</span></strong></dt>
<dd>
<p>A component of <span class="code">Dir</span> is not a directory. On some
platforms, <span class="code">enoent</span> is returned instead.</p>
</dd>
<dt><strong><span class="code">einval</span></strong></dt>
<dd>
<p>Attempt to delete the current directory. On some
platforms, <span class="code">eacces</span> is returned instead.</p>
</dd>
</dl>
</p></div>
<p><a name="delete-1"><span class="bold_code">delete(Filename) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Tries to delete the file <span class="code">Filename</span>. Returns <span class="code">ok</span>
if successful.</p>
<p>Typical error reasons are:</p>
<dl>
<dt><strong><span class="code">enoent</span></strong></dt>
<dd>
<p>The file does not exist.</p>
</dd>
<dt><strong><span class="code">eacces</span></strong></dt>
<dd>
<p>Missing permission for the file or one of its parents.</p>
</dd>
<dt><strong><span class="code">eperm</span></strong></dt>
<dd>
<p>The file is a directory and the user is not super-user.</p>
</dd>
<dt><strong><span class="code">enotdir</span></strong></dt>
<dd>
<p>A component of the file name is not a directory. On some
platforms, <span class="code">enoent</span> is returned instead.</p>
</dd>
<dt><strong><span class="code">einval</span></strong></dt>
<dd>
<p><span class="code">Filename</span> had an improper type, such as tuple.</p>
</dd>
</dl>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>In a future release, a bad type for the <span class="code">Filename</span>
argument will probably generate an exception.</p>
<p></p>
</p></div>
</div>
</p></div>
<p><a name="eval-1"><span class="bold_code">eval(Filename) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated | system_limit
| {Line, Mod, Term}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Line, Mod, Term -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Reads and evaluates Erlang expressions, separated by '.' (or
',', a sequence of expressions is also an expression), from
<span class="code">Filename</span>. The actual result of the evaluation is not
returned; any expression sequence in the file must be there
for its side effect. Returns one of the following:</p>
<dl>
<dt><strong><span class="code">ok</span></strong></dt>
<dd>
<p>The file was read and evaluated.</p>
</dd>
<dt><strong><span class="code">{error, atom()}</span></strong></dt>
<dd>
<p>An error occurred when opening the file or reading it.
See <span class="code">open/2</span> for a list of typical error codes.</p>
</dd>
<dt><strong><span class="code">{error, {Line, Mod, Term}}</span></strong></dt>
<dd>
<p>An error occurred when interpreting the Erlang
expressions in the file. Use <span class="code">format_error/1</span> to
convert the three-element tuple to an English description
of the error.</p>
</dd>
</dl>
</p></div>
<p><a name="eval-2"><span class="bold_code">eval(Filename, Bindings) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Bindings -- see erl_eval(3)</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated | system_limit
| {Line, Mod, Term}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Line, Mod, Term -- see eval/1</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>The same as <span class="code">eval/1</span> but the variable bindings
<span class="code">Bindings</span> are used in the evaluation. See
<span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','stdlib','erl_eval.html');">erl_eval(3)</a></span> about
variable bindings.</p>
</p></div>
<p><a name="file_info-1"><span class="bold_code">file_info(Filename) -> {ok, FileInfo} | {error, Reason}</span></a><br></p>
<div class="REFBODY"><p>
<p>This function is obsolete. Use <span class="code">read_file_info/1</span>
instead.</p>
</p></div>
<p><a name="format_error-1"><span class="bold_code">format_error(Reason) -> Chars</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Reason = atom() | {Line, Mod, Term}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Line, Mod, Term -- see eval/1</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Chars = [char() | Chars]</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Given the error reason returned by any function in this
module, returns a descriptive string of the error in English.</p>
</p></div>
<p><a name="get_cwd-0"><span class="bold_code">get_cwd() -> {ok, Dir} | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Dir = string()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = posix()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">{ok, Dir}</span>, where <span class="code">Dir</span> is the current
working directory of the file server.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>In rare circumstances, this function can fail on Unix.
It may happen if read permission does not exist for
the parent directories of the current directory.</p>
</p></div>
</div>
<p>Typical error reasons are:</p>
<dl>
<dt><strong><span class="code">eacces</span></strong></dt>
<dd>
<p>Missing read permission for one of the parents of
the current directory.</p>
</dd>
</dl>
</p></div>
<p><a name="get_cwd-1"><span class="bold_code">get_cwd(Drive) -> {ok, Dir} | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Drive = string() -- see below</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Dir = string()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p><span class="code">Drive</span> should be of the form "<span class="code">Letter</span><span class="code">:</span>",
for example "c:". Returns <span class="code">{ok, Dir}</span> or
<span class="code">{error, Reason}</span>, where <span class="code">Dir</span> is the current
working directory of the drive specified.</p>
<p>This function returns <span class="code">{error, enotsup}</span> on platforms
which have no concept of current drive (Unix, for example).</p>
<p>Typical error reasons are:</p>
<dl>
<dt><strong><span class="code">enotsup</span></strong></dt>
<dd>
<p>The operating system have no concept of drives.</p>
</dd>
<dt><strong><span class="code">eacces</span></strong></dt>
<dd>
<p>The drive does not exist.</p>
</dd>
<dt><strong><span class="code">einval</span></strong></dt>
<dd>
<p>The format of <span class="code">Drive</span> is invalid.</p>
</dd>
</dl>
</p></div>
<p><a name="list_dir-1"><span class="bold_code">list_dir(Dir) -> {ok, Filenames} | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Dir = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Filenames = [Filename]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Filename = string()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Lists all the files in a directory. Returns
<span class="code">{ok, Filenames}</span> if successful. Otherwise, it returns
<span class="code">{error, Reason}</span>. <span class="code">Filenames</span> is a list of
the names of all the files in the directory. The names are
not sorted.</p>
<p>Typical error reasons are:</p>
<dl>
<dt><strong><span class="code">eacces</span></strong></dt>
<dd>
<p>Missing search or write permissions for <span class="code">Dir</span> or
one of its parent directories.</p>
</dd>
<dt><strong><span class="code">enoent</span></strong></dt>
<dd>
<p>The directory does not exist.</p>
</dd>
</dl>
</p></div>
<p><a name="make_dir-1"><span class="bold_code">make_dir(Dir) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Dir = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Tries to create the directory <span class="code">Dir</span>. Missing parent
directories are <strong>not</strong> created. Returns <span class="code">ok</span> if
successful.</p>
<p>Typical error reasons are:</p>
<dl>
<dt><strong><span class="code">eacces</span></strong></dt>
<dd>
<p>Missing search or write permissions for the parent
directories of <span class="code">Dir</span>.</p>
</dd>
<dt><strong><span class="code">eexist</span></strong></dt>
<dd>
<p>There is already a file or directory named <span class="code">Dir</span>.</p>
</dd>
<dt><strong><span class="code">enoent</span></strong></dt>
<dd>
<p>A component of <span class="code">Dir</span> does not exist.</p>
</dd>
<dt><strong><span class="code">enospc</span></strong></dt>
<dd>
<p>There is a no space left on the device.</p>
</dd>
<dt><strong><span class="code">enotdir</span></strong></dt>
<dd>
<p>A component of <span class="code">Dir</span> is not a directory. On some
platforms, <span class="code">enoent</span> is returned instead.</p>
</dd>
</dl>
</p></div>
<p><a name="make_link-2"><span class="bold_code">make_link(Existing, New) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Existing = New = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Makes a hard link from <span class="code">Existing</span> to <span class="code">New</span>, on
platforms that support links (Unix). This function returns
<span class="code">ok</span> if the link was successfully created, or
<span class="code">{error, Reason}</span>. On platforms that do not support
links, <span class="code">{error,enotsup}</span> is returned.</p>
<p>Typical error reasons:</p>
<dl>
<dt><strong><span class="code">eacces</span></strong></dt>
<dd>
<p>Missing read or write permissions for the parent
directories of <span class="code">Existing</span> or <span class="code">New</span>.</p>
</dd>
<dt><strong><span class="code">eexist</span></strong></dt>
<dd>
<p><span class="code">New</span> already exists.</p>
</dd>
<dt><strong><span class="code">enotsup</span></strong></dt>
<dd>
<p>Hard links are not supported on this platform.</p>
</dd>
</dl>
</p></div>
<p><a name="make_symlink-2"><span class="bold_code">make_symlink(Name1, Name2) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Name1 = Name2 = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>This function creates a symbolic link <span class="code">Name2</span> to
the file or directory <span class="code">Name1</span>, on platforms that support
symbolic links (most Unix systems). <span class="code">Name1</span> need not
exist. This function returns <span class="code">ok</span> if the link was
successfully created, or <span class="code">{error, Reason}</span>. On platforms
that do not support symbolic links, <span class="code">{error, enotsup}</span>
is returned.</p>
<p>Typical error reasons:</p>
<dl>
<dt><strong><span class="code">eacces</span></strong></dt>
<dd>
<p>Missing read or write permissions for the parent
directories of <span class="code">Name1</span> or <span class="code">Name2</span>.</p>
</dd>
<dt><strong><span class="code">eexist</span></strong></dt>
<dd>
<p><span class="code">Name2</span> already exists.</p>
</dd>
<dt><strong><span class="code">enotsup</span></strong></dt>
<dd>
<p>Symbolic links are not supported on this platform.</p>
</dd>
</dl>
</p></div>
<p><a name="open-2"><span class="bold_code">open(Filename, Modes) -> {ok, IoDevice} | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Modes = [Mode]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Mode = read | write | append | raw | binary | {delayed_write, Size, Delay} | delayed_write | {read_ahead, Size} | read_ahead | compressed</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Size = Delay = int()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">IoDevice = io_device()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | system_limit</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Opens the file <span class="code">Filename</span> in the mode determined by
<span class="code">Modes</span>, which may contain one or more of the following
items:</p>
<dl>
<dt><strong><span class="code">read</span></strong></dt>
<dd>
<p>The file, which must exist, is opened for reading.</p>
</dd>
<dt><strong><span class="code">write</span></strong></dt>
<dd>
<p>The file is opened for writing. It is created if it does
not exist. If the file exists, and if <span class="code">write</span> is not
combined with <span class="code">read</span>, the file will be truncated.</p>
</dd>
<dt><strong><span class="code">append</span></strong></dt>
<dd>
<p>The file will be opened for writing, and it will be
created if it does not exist. Every write operation to a
file opened with <span class="code">append</span> will take place at
the end of the file.</p>
</dd>
<dt><strong><span class="code">raw</span></strong></dt>
<dd>
<p>The <span class="code">raw</span> option allows faster access to a file,
because no Erlang process is needed to handle the file.
However, a file opened in this way has the following
limitations:</p>
<ul>
<li>The functions in the <span class="code">io</span> module cannot be used,
because they can only talk to an Erlang process.
Instead, use the <span class="code">read/2</span>, <span class="code">read_line/1</span> and
<span class="code">write/2</span>
functions.</li>
<li>Especially if <span class="code">read_line/1</span> is to be used on a <span class="code">raw</span> file, it is recommended to combine this option with the <span class="code">{read_ahead, Size}</span> option as line oriented I/O is inefficient without buffering.</li>
<li>Only the Erlang process which opened the file can use
it.</li>
<li>A remote Erlang file server cannot be used;
the computer on which the Erlang node is running must
have access to the file system (directly or through
NFS).</li>
</ul>
</dd>
<dt><strong><span class="code">binary</span></strong></dt>
<dd>
<p>When this option has been given, read operations on the file
will return binaries rather than lists.</p>
</dd>
<dt><strong><span class="code">{delayed_write, Size, Delay}</span></strong></dt>
<dd>
<p>If this option is used, the data in subsequent
<span class="code">write/2</span> calls is buffered until there are at least
<span class="code">Size</span> bytes buffered, or until the oldest buffered
data is <span class="code">Delay</span> milliseconds old. Then all buffered
data is written in one operating system call.
The buffered data is also flushed before some other file
operation than <span class="code">write/2</span> is executed.</p>
<p>The purpose of this option is to increase performance
by reducing the number of operating system calls, so the
<span class="code">write/2</span> calls should be for sizes significantly
less than <span class="code">Size</span>, and not interspersed by to many
other file operations, for this to happen.</p>
<p>When this option is used, the result of <span class="code">write/2</span>
calls may prematurely be reported as successful, and if
a write error should actually occur the error is
reported as the result of the next file operation, which
is not executed.</p>
<p>For example, when <span class="code">delayed_write</span> is used, after a
number of <span class="code">write/2</span> calls, <span class="code">close/1</span> might
return <span class="code">{error, enospc}</span> because there was not enough
space on the disc for previously written data, and
<span class="code">close/1</span> should probably be called again since the
file is still open.</p>
</dd>
<dt><strong><span class="code">delayed_write</span></strong></dt>
<dd>
<p>The same as <span class="code">{delayed_write, Size, Delay}</span> with
reasonable default values for <span class="code">Size</span> and
<span class="code">Delay</span>. (Roughly some 64 KBytes, 2 seconds)</p>
</dd>
<dt><strong><span class="code">{read_ahead, Size}</span></strong></dt>
<dd>
<p>This option activates read data buffering. If
<span class="code">read/2</span> calls are for significantly less than
<span class="code">Size</span> bytes, read operations towards the operating
system are still performed for blocks of <span class="code">Size</span>
bytes. The extra data is buffered and returned in
subsequent <span class="code">read/2</span> calls, giving a performance gain
since the number of operating system calls is reduced.</p>
<p>The <span class="code">read_ahead</span> buffer is also highly utilized
by the <span class="code">read_line/1</span> function in <span class="code">raw</span> mode,
why this option is recommended (for performance reasons)
when accessing raw files using that function.</p>
<p>If <span class="code">read/2</span> calls are for sizes not significantly
less than, or even greater than <span class="code">Size</span> bytes, no
performance gain can be expected.</p>
</dd>
<dt><strong><span class="code">read_ahead</span></strong></dt>
<dd>
<p>The same as <span class="code">{read_ahead, Size}</span> with a reasonable
default value for <span class="code">Size</span>. (Roughly some 64 KBytes)</p>
</dd>
<dt><strong><span class="code">compressed</span></strong></dt>
<dd>
<p>Makes it possible to read or write gzip compressed
files. The <span class="code">compressed</span> option must be combined
with either <span class="code">read</span> or <span class="code">write</span>, but not both.
Note that the file size obtained with
<span class="code">read_file_info/1</span> will most probably not match the
number of bytes that can be read from a compressed file.</p>
</dd>
<dt><strong><span class="code">{encoding, Encoding}</span></strong></dt>
<dd>
<p>Makes the file perform automatic translation of characters to and from a specific (Unicode) encoding. Note that the data supplied to file:write or returned by file:read still is byte oriented, this option only denotes how data is actually stored in the disk file.</p>
<p>Depending on the encoding, different methods of reading and writing data is preferred. The default encoding of <span class="code">latin1</span> implies using this (the file) module for reading and writing data, as the interfaces provided here work with byte-oriented data, while using other (Unicode) encodings makes the <span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','stdlib','io.html');">io(3)</a></span> module's <span class="code">get_chars</span>, <span class="code">get_line</span> and <span class="code">put_chars</span> functions more suitable, as they can work with the full Unicode range.</p>
<p>If data is sent to an <span class="code">io_device()</span> in a format that cannot be converted to the specified encoding, or if data is read by a function that returns data in a format that cannot cope with the character range of the data, an error occurs and the file will be closed.</p>
<p>The allowed values for <span class="code">Encoding</span> are:</p>
<dl>
<dt><strong><span class="code">latin1</span></strong></dt>
<dd>
<p>The default encoding. Bytes supplied to i.e. file:write are written as is on the file, likewise bytes read from the file are returned to i.e. file:read as is. If the <span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','stdlib','io.html');">io(3)</a></span> module is used for writing, the file can only cope with Unicode characters up to codepoint 255 (the ISO-latin-1 range).</p>
</dd>
<dt><strong><span class="code">unicode</span> or <span class="code">utf8</span></strong></dt>
<dd>
<p>Characters are translated to and from the UTF-8 encoding before being written to or read from the file. A file opened in this way might be readable using the file:read function, as long as no data stored on the file lies beyond the ISO-latin-1 range (0..255), but failure will occur if the data contains Unicode codepoints beyond that range. The file is best read with the functions in the Unicode aware <span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','stdlib','io.html');">io(3)</a></span> module.</p>
<p>Bytes written to the file by any means are translated to UTF-8 encoding before actually being stored on the disk file.</p>
</dd>
<dt><strong><span class="code">utf16</span> or <span class="code">{utf16,big}</span></strong></dt>
<dd>
<p>Works like <span class="code">unicode</span>, but translation is done to and from big endian UTF-16 instead of UTF-8.</p>
</dd>
<dt><strong><span class="code">{utf16,little}</span></strong></dt>
<dd>
<p>Works like <span class="code">unicode</span>, but translation is done to and from little endian UTF-16 instead of UTF-8.</p>
</dd>
<dt><strong><span class="code">utf32</span> or <span class="code">{utf32,big}</span></strong></dt>
<dd>
<p>Works like <span class="code">unicode</span>, but translation is done to and from big endian UTF-32 instead of UTF-8.</p>
</dd>
<dt><strong><span class="code">{utf32,little}</span></strong></dt>
<dd>
<p>Works like <span class="code">unicode</span>, but translation is done to and from little endian UTF-32 instead of UTF-8.</p>
</dd>
</dl>
<p>The Encoding can be changed for a file "on the fly" by using the <span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','stdlib','io.html#setopts-2');">io:setopts/2</a></span> function, why a file can be analyzed in latin1 encoding for i.e. a BOM, positioned beyond the BOM and then be set for the right encoding before further reading.See the <span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','stdlib','unicode.html');">unicode(3)</a></span> module for functions identifying BOM's.</p>
<p>This option is not allowed on <span class="code">raw</span> files.</p>
</dd>
</dl>
<p>Returns:</p>
<dl>
<dt><strong><span class="code">{ok, IoDevice}</span></strong></dt>
<dd>
<p>The file has been opened in the requested mode.
<span class="code">IoDevice</span> is a reference to the file.</p>
</dd>
<dt><strong><span class="code">{error, Reason}</span></strong></dt>
<dd>
<p>The file could not be opened.</p>
</dd>
</dl>
<p><span class="code">IoDevice</span> is really the pid of the process which
handles the file. This process is linked to the process
which originally opened the file. If any process to which
the <span class="code">IoDevice</span> is linked terminates, the file will be
closed and the process itself will be terminated.
An <span class="code">IoDevice</span> returned from this call can be used as an
argument to the IO functions (see
<span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','stdlib','io.html');">io(3)</a></span>).</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>In previous versions of <span class="code">file</span>, modes were given
as one of the atoms <span class="code">read</span>, <span class="code">write</span>, or
<span class="code">read_write</span> instead of a list. This is still allowed
for reasons of backwards compatibility, but should not be
used for new code. Also note that <span class="code">read_write</span> is not
allowed in a mode list.</p>
</p></div>
</div>
<p>Typical error reasons:</p>
<dl>
<dt><strong><span class="code">enoent</span></strong></dt>
<dd>
<p>The file does not exist.</p>
</dd>
<dt><strong><span class="code">eacces</span></strong></dt>
<dd>
<p>Missing permission for reading the file or searching one
of the parent directories.</p>
</dd>
<dt><strong><span class="code">eisdir</span></strong></dt>
<dd>
<p>The named file is not a regular file. It may be a
directory, a fifo, or a device.</p>
</dd>
<dt><strong><span class="code">enotdir</span></strong></dt>
<dd>
<p>A component of the file name is not a directory. On some
platforms, <span class="code">enoent</span> is returned instead.</p>
</dd>
<dt><strong><span class="code">enospc</span></strong></dt>
<dd>
<p>There is a no space left on the device (if <span class="code">write</span>
access was specified).</p>
</dd>
</dl>
</p></div>
<p><a name="path_consult-2"><span class="bold_code">path_consult(Path, Filename) -> {ok, Terms, FullName} | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Path = [Dir]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Dir = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Terms = [term()]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">FullName = string()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated | system_limit
| {Line, Mod, Term}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Line, Mod, Term -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Searches the path <span class="code">Path</span> (a list of directory names)
until the file <span class="code">Filename</span> is found. If <span class="code">Filename</span>
is an absolute filename, <span class="code">Path</span> is ignored.
Then reads Erlang terms, separated by '.', from the file.
Returns one of the following:</p>
<dl>
<dt><strong><span class="code">{ok, Terms, FullName}</span></strong></dt>
<dd>
<p>The file was successfully read. <span class="code">FullName</span> is
the full name of the file.</p>
</dd>
<dt><strong><span class="code">{error, enoent}</span></strong></dt>
<dd>
<p>The file could not be found in any of the directories in
<span class="code">Path</span>.</p>
</dd>
<dt><strong><span class="code">{error, atom()}</span></strong></dt>
<dd>
<p>An error occurred when opening the file or reading it.
See <span class="bold_code"><a href="#open-2">open/2</a></span> for a list
of typical error codes.</p>
</dd>
<dt><strong><span class="code">{error, {Line, Mod, Term}}</span></strong></dt>
<dd>
<p>An error occurred when interpreting the Erlang terms in
the file. Use <span class="code">format_error/1</span> to convert
the three-element tuple to an English description of
the error.</p>
</dd>
</dl>
</p></div>
<p><a name="path_eval-2"><span class="bold_code">path_eval(Path, Filename) -> {ok, FullName} | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Path = [Dir]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Dir = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">FullName = string()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated | system_limit
| {Line, Mod, Term}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Line, Mod, Term -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Searches the path <span class="code">Path</span> (a list of directory names)
until the file <span class="code">Filename</span> is found. If <span class="code">Filename</span>
is an absolute file name, <span class="code">Path</span> is ignored. Then reads
and evaluates Erlang expressions, separated by '.' (or ',', a
sequence of expressions is also an expression), from the file.
The actual result of evaluation is not returned; any
expression sequence in the file must be there for its side
effect. Returns one of the following:</p>
<dl>
<dt><strong><span class="code">{ok, FullName}</span></strong></dt>
<dd>
<p>The file was read and evaluated. <span class="code">FullName</span> is
the full name of the file.</p>
</dd>
<dt><strong><span class="code">{error, enoent}</span></strong></dt>
<dd>
<p>The file could not be found in any of the directories in
<span class="code">Path</span>.</p>
</dd>
<dt><strong><span class="code">{error, atom()}</span></strong></dt>
<dd>
<p>An error occurred when opening the file or reading it.
See <span class="bold_code"><a href="#open-2">open/2</a></span> for a list
of typical error codes.</p>
</dd>
<dt><strong><span class="code">{error, {Line, Mod, Term}}</span></strong></dt>
<dd>
<p>An error occurred when interpreting the Erlang
expressions in the file. Use <span class="code">format_error/1</span> to
convert the three-element tuple to an English description
of the error.</p>
</dd>
</dl>
</p></div>
<p><a name="path_open-3"><span class="bold_code">path_open(Path, Filename, Modes) -> {ok, IoDevice, FullName} | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Path = [Dir]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Dir = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Modes = [Mode] -- see open/2</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">IoDevice = io_device()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">FullName = string()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | system_limit</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Searches the path <span class="code">Path</span> (a list of directory names)
until the file <span class="code">Filename</span> is found. If <span class="code">Filename</span>
is an absolute file name, <span class="code">Path</span> is ignored.
Then opens the file in the mode determined by <span class="code">Modes</span>.
Returns one of the following:</p>
<dl>
<dt><strong><span class="code">{ok, IoDevice, FullName}</span></strong></dt>
<dd>
<p>The file has been opened in the requested mode.
<span class="code">IoDevice</span> is a reference to the file and
<span class="code">FullName</span> is the full name of the file.</p>
</dd>
<dt><strong><span class="code">{error, enoent}</span></strong></dt>
<dd>
<p>The file could not be found in any of the directories in
<span class="code">Path</span>.</p>
</dd>
<dt><strong><span class="code">{error, atom()}</span></strong></dt>
<dd>
<p>The file could not be opened.</p>
</dd>
</dl>
</p></div>
<p><a name="path_script-2"><span class="bold_code">path_script(Path, Filename) -> {ok, Value, FullName} | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Path = [Dir]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Dir = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Value = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">FullName = string()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated | system_limit
| {Line, Mod, Term}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Line, Mod, Term -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Searches the path <span class="code">Path</span> (a list of directory names)
until the file <span class="code">Filename</span> is found. If <span class="code">Filename</span>
is an absolute file name, <span class="code">Path</span> is ignored. Then reads
and evaluates Erlang expressions, separated by '.' (or ',', a
sequence of expressions is also an expression), from the file.
Returns one of the following:</p>
<dl>
<dt><strong><span class="code">{ok, Value, FullName}</span></strong></dt>
<dd>
<p>The file was read and evaluated. <span class="code">FullName</span> is
the full name of the file and <span class="code">Value</span> the value of
the last expression.</p>
</dd>
<dt><strong><span class="code">{error, enoent}</span></strong></dt>
<dd>
<p>The file could not be found in any of the directories in
<span class="code">Path</span>.</p>
</dd>
<dt><strong><span class="code">{error, atom()}</span></strong></dt>
<dd>
<p>An error occurred when opening the file or reading it.
See <span class="bold_code"><a href="#open-2">open/2</a></span> for a list
of typical error codes.</p>
</dd>
<dt><strong><span class="code">{error, {Line, Mod, Term}}</span></strong></dt>
<dd>
<p>An error occurred when interpreting the Erlang
expressions in the file. Use <span class="code">format_error/1</span> to
convert the three-element tuple to an English description
of the error.</p>
</dd>
</dl>
</p></div>
<p><a name="path_script-3"><span class="bold_code">path_script(Path, Filename, Bindings) -> {ok, Value, FullName} | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Path = [Dir]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Dir = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Bindings -- see erl_eval(3)</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Value = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">FullName = string()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = posix() | terminated | system_limit
| {Line, Mod, Term}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Line, Mod, Term -- see path_script/2</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>The same as <span class="code">path_script/2</span> but the variable bindings
<span class="code">Bindings</span> are used in the evaluation. See
<span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','stdlib','erl_eval.html');">erl_eval(3)</a></span> about
variable bindings.</p>
</p></div>
<p><a name="pid2name-1"><span class="bold_code">pid2name(Pid) -> string() | undefined</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Pid = pid()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>If <span class="code">Pid</span> is an IO device, that is, a pid returned from
<span class="code">open/2</span>, this function returns the filename, or rather:</p>
<dl>
<dt><strong><span class="code">{ok, Filename}</span></strong></dt>
<dd>
<p>If this node's file server is not a slave, the file was
opened by this node's file server, (this implies that
<span class="code">Pid</span> must be a local pid) and the file is not
closed. <span class="code">Filename</span> is the filename in flat string
format.</p>
</dd>
<dt><strong><span class="code">undefined</span></strong></dt>
<dd>
<p>In all other cases.</p>
</dd>
</dl>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>This function is intended for debugging only.</p>
</p></div>
</div>
</p></div>
<p><a name="position-2"><span class="bold_code">position(IoDevice, Location) -> {ok, NewPosition} | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">IoDevice = io_device()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Location = Offset | {bof, Offset} | {cur, Offset} | {eof, Offset} | bof | cur | eof</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Offset = int()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">NewPosition = int()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Sets the position of the file referenced by <span class="code">IoDevice</span>
to <span class="code">Location</span>. Returns <span class="code">{ok, NewPosition}</span> (as
absolute offset) if successful, otherwise
<span class="code">{error, Reason}</span>. <span class="code">Location</span> is one of
the following:</p>
<dl>
<dt><strong><span class="code">Offset</span></strong></dt>
<dd>
<p>The same as <span class="code">{bof, Offset}</span>.</p>
</dd>
<dt><strong><span class="code">{bof, Offset}</span></strong></dt>
<dd>
<p>Absolute offset.</p>
</dd>
<dt><strong><span class="code">{cur, Offset}</span></strong></dt>
<dd>
<p>Offset from the current position.</p>
</dd>
<dt><strong><span class="code">{eof, Offset}</span></strong></dt>
<dd>
<p>Offset from the end of file.</p>
</dd>
<dt><strong><span class="code">bof | cur | eof</span></strong></dt>
<dd>
<p>The same as above with <span class="code">Offset</span> 0.</p>
</dd>
</dl>
<p>Note that offsets are counted in bytes, not in characters. If the file is opened using some other <span class="code">encoding</span> than <span class="code">latin1</span>, one byte does not correspond to one character. Positioning in such a file can only be done to known character boundaries, i.e. to a position earlier retrieved by getting a current position, to the beginning/end of the file or to some other position <strong>known</strong> to be on a correct character boundary by some other means (typically beyond a byte order mark in the file, which has a known byte-size).</p>
<p>Typical error reasons are:</p>
<dl>
<dt><strong><span class="code">einval</span></strong></dt>
<dd>
<p>Either <span class="code">Location</span> was illegal, or it evaluated to a
negative offset in the file. Note that if the resulting
position is a negative value, the result is an error, and
after the call the file position is undefined.</p>
</dd>
</dl>
</p></div>
<p><a name="pread-2"><span class="bold_code">pread(IoDevice, LocNums) -> {ok, DataL} | eof | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">IoDevice = io_device()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">LocNums = [{Location, Number}]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Location -- see position/2</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Number = int()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">DataL = [Data]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Data = [char()] | binary()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Performs a sequence of <span class="code">pread/3</span> in one operation,
which is more efficient than calling them one at a time.
Returns <span class="code">{ok, [Data, ...]}</span> or <span class="code">{error, Reason}</span>,
where each <span class="code">Data</span>, the result of the corresponding
<span class="code">pread</span>, is either a list or a binary depending on
the mode of the file, or <span class="code">eof</span> if the requested position
was beyond end of file.</p>
<p>As the position is given as a byte-offset, special caution has to be taken when working with files where <span class="code">encoding</span> is set to something else than <span class="code">latin1</span>, as not every byte position will be a valid character boundary on such a file.</p>
</p></div>
<p><a name="pread-3"><span class="bold_code">pread(IoDevice, Location, Number) -> {ok, Data} | eof | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">IoDevice = io_device()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Location -- see position/2</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Number = int()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Data = [char()] | binary()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Combines <span class="code">position/2</span> and <span class="code">read/2</span> in one
operation, which is more efficient than calling them one at a
time. If <span class="code">IoDevice</span> has been opened in raw mode, some
restrictions apply: <span class="code">Location</span> is only allowed to be an
integer; and the current position of the file is undefined
after the operation.</p>
<p>As the position is given as a byte-offset, special caution has to be taken when working with files where <span class="code">encoding</span> is set to something else than <span class="code">latin1</span>, as not every byte position will be a valid character boundary on such a file.</p>
</p></div>
<p><a name="pwrite-2"><span class="bold_code">pwrite(IoDevice, LocBytes) -> ok | {error, {N, Reason}}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">IoDevice = io_device()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">LocBytes = [{Location, Bytes}]</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Location -- see position/2</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Bytes = iodata()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">N = int()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Performs a sequence of <span class="code">pwrite/3</span> in one operation,
which is more efficient than calling them one at a time.
Returns <span class="code">ok</span> or <span class="code">{error, {N, Reason}}</span>, where
<span class="code">N</span> is the number of successful writes that was done
before the failure.</p>
<p>When positioning in a file with other <span class="code">encoding</span> than <span class="code">latin1</span>, caution must be taken to set the position on a correct character boundary, see <span class="bold_code"><a href="#position-2">position/2</a></span> for details.</p>
</p></div>
<p><a name="pwrite-3"><span class="bold_code">pwrite(IoDevice, Location, Bytes) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">IoDevice = io_device()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Location -- see position/2</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Bytes = iodata()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Combines <span class="code">position/2</span> and <span class="code">write/2</span> in one
operation, which is more efficient than calling them one at a
time. If <span class="code">IoDevice</span> has been opened in raw mode, some
restrictions apply: <span class="code">Location</span> is only allowed to be an
integer; and the current position of the file is undefined
after the operation.</p>
<p>When positioning in a file with other <span class="code">encoding</span> than <span class="code">latin1</span>, caution must be taken to set the position on a correct character boundary, see <span class="bold_code"><a href="#position-2">position/2</a></span> for details.</p>
</p></div>
<p><a name="read-2"><span class="bold_code">read(IoDevice, Number) -> {ok, Data} | eof | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">IoDevice = io_device()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Number = int()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Data = [char()] | binary()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Reads <span class="code">Number</span> bytes/characters from the file referenced by
<span class="code">IoDevice</span>. The functions <span class="code">read/2</span>, <span class="code">pread/3</span>
and <span class="code">read_line/1</span> are the only ways to read from a file
opened in raw mode (although they work for normally opened
files, too).</p>
<p>For files where <span class="code">encoding</span> is set to something else than <span class="code">latin1</span>, one character might be represented by more than one byte on the file. The parameter <span class="code">Number</span> always denotes the number of <strong>characters</strong> read from the file, why the position in the file might be moved a lot more than this number when reading a Unicode file.</p>
<p>Also if <span class="code">encoding</span> is set to something else than <span class="code">latin1</span>, the <span class="code">read/3</span> call will fail if the data contains characters larger than 255, why the <span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','stdlib','io.html');">io(3)</a></span> module is to be preferred when reading such a file.</p>
<p>The function returns:</p>
<dl>
<dt><strong><span class="code">{ok, Data}</span></strong></dt>
<dd>
<p>If the file was opened in binary mode, the read bytes are
returned in a binary, otherwise in a list. The list or
binary will be shorter than the number of bytes requested
if end of file was reached.</p>
</dd>
<dt><strong><span class="code">eof</span></strong></dt>
<dd>
<p>Returned if <span class="code">Number>0</span> and end of file was reached
before anything at all could be read.</p>
</dd>
<dt><strong><span class="code">{error, Reason}</span></strong></dt>
<dd>
<p>An error occurred.</p>
</dd>
</dl>
<p>Typical error reasons:</p>
<dl>
<dt><strong><span class="code">ebadf</span></strong></dt>
<dd>
<p>The file is not opened for reading.</p>
</dd>
<dt><strong><span class="code">{no_translation, unicode, latin1}</span></strong></dt>
<dd>
<p>The file is was opened with another <span class="code">encoding</span> than <span class="code">latin1</span> and the data on the file can not be translated to the byte-oriented data that this function returns.</p>
</dd>
</dl>
</p></div>
<p><a name="read_file-1"><span class="bold_code">read_file(Filename) -> {ok, Binary} | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Binary = binary()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated | system_limit</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Returns <span class="code">{ok, Binary}</span>, where <span class="code">Binary</span> is a binary
data object that contains the contents of <span class="code">Filename</span>, or
<span class="code">{error, Reason}</span> if an error occurs.</p>
<p>Typical error reasons:</p>
<dl>
<dt><strong><span class="code">enoent</span></strong></dt>
<dd>
<p>The file does not exist.</p>
</dd>
<dt><strong><span class="code">eacces</span></strong></dt>
<dd>
<p>Missing permission for reading the file, or for
searching one of the parent directories.</p>
</dd>
<dt><strong><span class="code">eisdir</span></strong></dt>
<dd>
<p>The named file is a directory.</p>
</dd>
<dt><strong><span class="code">enotdir</span></strong></dt>
<dd>
<p>A component of the file name is not a directory. On some
platforms, <span class="code">enoent</span> is returned instead.</p>
</dd>
<dt><strong><span class="code">enomem</span></strong></dt>
<dd>
<p>There is not enough memory for the contents of the file.</p>
</dd>
</dl>
</p></div>
<p><a name="read_file_info-1"><span class="bold_code">read_file_info(Filename) -> {ok, FileInfo} | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">FileInfo = #file_info{}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Retrieves information about a file. Returns
<span class="code">{ok, FileInfo}</span> if successful, otherwise
<span class="code">{error, Reason}</span>. <span class="code">FileInfo</span> is a record
<span class="code">file_info</span>, defined in the Kernel include file
<span class="code">file.hrl</span>. Include the following directive in the module
from which the function is called:</p>
<div class="example"><pre>
-include_lib("kernel/include/file.hrl").</pre></div>
<p>The record <span class="code">file_info</span> contains the following fields.</p>
<dl>
<dt><strong><span class="code">size = int()</span></strong></dt>
<dd>
<p>Size of file in bytes.</p>
</dd>
<dt><strong><span class="code">type = device | directory | regular | other</span></strong></dt>
<dd>
<p>The type of the file.</p>
</dd>
<dt><strong><span class="code">access = read | write | read_write | none</span></strong></dt>
<dd>
<p>The current system access to the file.</p>
</dd>
<dt><strong><span class="code">atime = time()</span></strong></dt>
<dd>
<p>The last (local) time the file was read.</p>
</dd>
<dt><strong><span class="code">mtime = time()</span></strong></dt>
<dd>
<p>The last (local) time the file was written.</p>
</dd>
<dt><strong><span class="code">ctime = time()</span></strong></dt>
<dd>
<p>The interpretation of this time field depends on
the operating system. On Unix, it is the last time
the file or the inode was changed. In Windows, it is
the create time.</p>
</dd>
<dt><strong><span class="code">mode = int()</span></strong></dt>
<dd>
<p>The file permissions as the sum of the following bit
values:</p>
<dl>
<dt><strong>8#00400</strong></dt>
<dd>read permission: owner</dd>
<dt><strong>8#00200</strong></dt>
<dd>write permission: owner</dd>
<dt><strong>8#00100</strong></dt>
<dd>execute permission: owner</dd>
<dt><strong>8#00040</strong></dt>
<dd>read permission: group</dd>
<dt><strong>8#00020</strong></dt>
<dd>write permission: group</dd>
<dt><strong>8#00010</strong></dt>
<dd>execute permission: group</dd>
<dt><strong>8#00004</strong></dt>
<dd>read permission: other</dd>
<dt><strong>8#00002</strong></dt>
<dd>write permission: other</dd>
<dt><strong>8#00001</strong></dt>
<dd>execute permission: other</dd>
<dt><strong>16#800</strong></dt>
<dd>set user id on execution</dd>
<dt><strong>16#400</strong></dt>
<dd>set group id on execution</dd>
</dl>
<p>On Unix platforms, other bits than those listed above
may be set.</p>
</dd>
<dt><strong><span class="code">links = int()</span></strong></dt>
<dd>
<p>Number of links to the file (this will always be 1 for
file systems which have no concept of links).</p>
</dd>
<dt><strong><span class="code">major_device = int()</span></strong></dt>
<dd>
<p>Identifies the file system where the file is located.
In Windows, the number indicates a drive as follows:
0 means A:, 1 means B:, and so on.</p>
</dd>
<dt><strong><span class="code">minor_device = int()</span></strong></dt>
<dd>
<p>Only valid for character devices on Unix. In all other
cases, this field is zero.</p>
</dd>
<dt><strong><span class="code">inode = int()</span></strong></dt>
<dd>
<p>Gives the <span class="code">inode</span> number. On non-Unix file systems,
this field will be zero.</p>
</dd>
<dt><strong><span class="code">uid = int()</span></strong></dt>
<dd>
<p>Indicates the owner of the file. Will be zero for
non-Unix file systems.</p>
</dd>
<dt><strong><span class="code">gid = int()</span></strong></dt>
<dd>
<p>Gives the group that the owner of the file belongs to.
Will be zero for non-Unix file systems.</p>
</dd>
</dl>
<p>Typical error reasons:</p>
<dl>
<dt><strong><span class="code">eacces</span></strong></dt>
<dd>
<p>Missing search permission for one of the parent
directories of the file.</p>
</dd>
<dt><strong><span class="code">enoent</span></strong></dt>
<dd>
<p>The file does not exist.</p>
</dd>
<dt><strong><span class="code">enotdir</span></strong></dt>
<dd>
<p>A component of the file name is not a directory. On some
platforms, <span class="code">enoent</span> is returned instead.</p>
</dd>
</dl>
</p></div>
<p><a name="read_line-1"><span class="bold_code">read_line(IoDevice) -> {ok, Data} | eof | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">IoDevice = io_device()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Data = [char()] | binary()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Reads a line of bytes/characters from the file referenced by
<span class="code">IoDevice</span>. Lines are defined to be delimited by the linefeed (LF, <span class="code">\n</span>) character, but any carriage return (CR, <span class="code">\r</span>) followed by a newline is also treated as a single LF character (the carriage return is silently ignored). The line is returned <strong>including</strong> the LF, but excluding any CR immediately followed by a LF. This behaviour is consistent with the behaviour of <span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','stdlib','io.html#get_line-2');">io:get_line/2</a></span>. If end of file is reached without any LF ending the last line, a line with no trailing LF is returned.</p>
<p>The function can be used on files opened in <span class="code">raw</span> mode. It is however inefficient to use it on <span class="code">raw</span> files if the file is not opened with the option <span class="code">{read_ahead, Size}</span> specified, why combining <span class="code">raw</span> and <span class="code">{read_ahead, Size}</span> is highly recommended when opening a text file for raw line oriented reading.</p>
<p>If <span class="code">encoding</span> is set to something else than <span class="code">latin1</span>, the <span class="code">read_line/1</span> call will fail if the data contains characters larger than 255, why the <span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','stdlib','io.html');">io(3)</a></span> module is to be preferred when reading such a file.</p>
<p>The function returns:</p>
<dl>
<dt><strong><span class="code">{ok, Data}</span></strong></dt>
<dd>
<p>One line from the file is returned, including the trailing LF, but with CRLF sequences replaced by a single LF (see above).</p>
<p>If the file was opened in binary mode, the read bytes are
returned in a binary, otherwise in a list.</p>
</dd>
<dt><strong><span class="code">eof</span></strong></dt>
<dd>
<p>Returned if end of file was reached
before anything at all could be read.</p>
</dd>
<dt><strong><span class="code">{error, Reason}</span></strong></dt>
<dd>
<p>An error occurred.</p>
</dd>
</dl>
<p>Typical error reasons:</p>
<dl>
<dt><strong><span class="code">ebadf</span></strong></dt>
<dd>
<p>The file is not opened for reading.</p>
</dd>
<dt><strong><span class="code">{no_translation, unicode, latin1}</span></strong></dt>
<dd>
<p>The file is was opened with another <span class="code">encoding</span> than <span class="code">latin1</span> and the data on the file can not be translated to the byte-oriented data that this function returns.</p>
</dd>
</dl>
</p></div>
<p><a name="read_link-1"><span class="bold_code">read_link(Name) -> {ok, Filename} | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Name = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Filename = string()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>This function returns <span class="code">{ok, Filename}</span> if <span class="code">Name</span>
refers to a symbolic link or <span class="code">{error, Reason}</span> otherwise.
On platforms that do not support symbolic links, the return
value will be <span class="code">{error,enotsup}</span>.</p>
<p>Typical error reasons:</p>
<dl>
<dt><strong><span class="code">einval</span></strong></dt>
<dd>
<p><span class="code">Linkname</span> does not refer to a symbolic link.</p>
</dd>
<dt><strong><span class="code">enoent</span></strong></dt>
<dd>
<p>The file does not exist.</p>
</dd>
<dt><strong><span class="code">enotsup</span></strong></dt>
<dd>
<p>Symbolic links are not supported on this platform.</p>
</dd>
</dl>
</p></div>
<p><a name="read_link_info-1"><span class="bold_code">read_link_info(Name) -> {ok, FileInfo} | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Name = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">FileInfo = #file_info{}, see read_file_info/1</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>This function works like <span class="code">read_file_info/1</span>, except that
if <span class="code">Name</span> is a symbolic link, information about the link
will be returned in the <span class="code">file_info</span> record and
the <span class="code">type</span> field of the record will be set to
<span class="code">symlink</span>.</p>
<p>If <span class="code">Name</span> is not a symbolic link, this function returns
exactly the same result as <span class="code">read_file_info/1</span>.
On platforms that do not support symbolic links, this function
is always equivalent to <span class="code">read_file_info/1</span>.</p>
</p></div>
<p><a name="rename-2"><span class="bold_code">rename(Source, Destination) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Source = Destination = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Tries to rename the file <span class="code">Source</span> to <span class="code">Destination</span>.
It can be used to move files (and directories) between
directories, but it is not sufficient to specify
the destination only. The destination file name must also be
specified. For example, if <span class="code">bar</span> is a normal file and
<span class="code">foo</span> and <span class="code">baz</span> are directories,
<span class="code">rename("foo/bar", "baz")</span> returns an error, but
<span class="code">rename("foo/bar", "baz/bar")</span> succeeds. Returns
<span class="code">ok</span> if it is successful.</p>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>Renaming of open files is not allowed on most platforms
(see <span class="code">eacces</span> below).</p>
</p></div>
</div>
<p>Typical error reasons:</p>
<dl>
<dt><strong><span class="code">eacces</span></strong></dt>
<dd>
<p>Missing read or write permissions for the parent
directories of <span class="code">Source</span> or <span class="code">Destination</span>. On
some platforms, this error is given if either
<span class="code">Source</span> or <span class="code">Destination</span> is open.</p>
</dd>
<dt><strong><span class="code">eexist</span></strong></dt>
<dd>
<p><span class="code">Destination</span> is not an empty directory. On some
platforms, also given when <span class="code">Source</span> and
<span class="code">Destination</span> are not of the same type.</p>
</dd>
<dt><strong><span class="code">einval</span></strong></dt>
<dd>
<p><span class="code">Source</span> is a root directory, or <span class="code">Destination</span>
is a sub-directory of <span class="code">Source</span>.</p>
</dd>
<dt><strong><span class="code">eisdir</span></strong></dt>
<dd>
<p><span class="code">Destination</span> is a directory, but <span class="code">Source</span> is
not.</p>
</dd>
<dt><strong><span class="code">enoent</span></strong></dt>
<dd>
<p><span class="code">Source</span> does not exist.</p>
</dd>
<dt><strong><span class="code">enotdir</span></strong></dt>
<dd>
<p><span class="code">Source</span> is a directory, but <span class="code">Destination</span> is
not.</p>
</dd>
<dt><strong><span class="code">exdev</span></strong></dt>
<dd>
<p><span class="code">Source</span> and <span class="code">Destination</span> are on different
file systems.</p>
</dd>
</dl>
</p></div>
<p><a name="script-1"><span class="bold_code">script(Filename) -> {ok, Value} | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Value = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated | system_limit
| {Line, Mod, Term}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Line, Mod, Term -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Reads and evaluates Erlang expressions, separated by '.' (or
',', a sequence of expressions is also an expression), from
the file. Returns one of the following:</p>
<dl>
<dt><strong><span class="code">{ok, Value}</span></strong></dt>
<dd>
<p>The file was read and evaluated. <span class="code">Value</span> is
the value of the last expression.</p>
</dd>
<dt><strong><span class="code">{error, atom()}</span></strong></dt>
<dd>
<p>An error occurred when opening the file or reading it.
See <span class="bold_code"><a href="#open-2">open/2</a></span> for a list
of typical error codes.</p>
</dd>
<dt><strong><span class="code">{error, {Line, Mod, Term}}</span></strong></dt>
<dd>
<p>An error occurred when interpreting the Erlang
expressions in the file. Use <span class="code">format_error/1</span> to
convert the three-element tuple to an English description
of the error.</p>
</dd>
</dl>
</p></div>
<p><a name="script-2"><span class="bold_code">script(Filename, Bindings) -> {ok, Value} | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Bindings -- see erl_eval(3)</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Value = term()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated | system_limit
| {Line, Mod, Term}</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code"> Line, Mod, Term -- see below</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>The same as <span class="code">script/1</span> but the variable bindings
<span class="code">Bindings</span> are used in the evaluation. See
<span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','stdlib','erl_eval.html');">erl_eval(3)</a></span> about
variable bindings.</p>
</p></div>
<p><a name="set_cwd-1"><span class="bold_code">set_cwd(Dir) -> ok | {error,Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Dir = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Sets the current working directory of the file server to
<span class="code">Dir</span>. Returns <span class="code">ok</span> if successful.</p>
<p>Typical error reasons are:</p>
<dl>
<dt><strong><span class="code">enoent</span></strong></dt>
<dd>
<p>The directory does not exist.</p>
</dd>
<dt><strong><span class="code">enotdir</span></strong></dt>
<dd>
<p>A component of <span class="code">Dir</span> is not a directory. On some
platforms, <span class="code">enoent</span> is returned.</p>
</dd>
<dt><strong><span class="code">eacces</span></strong></dt>
<dd>
<p>Missing permission for the directory or one of its
parents.</p>
</dd>
<dt><strong><span class="code">badarg</span></strong></dt>
<dd>
<p><span class="code">Filename</span> had an improper type, such as tuple.</p>
</dd>
</dl>
<div class="warning">
<div class="label">Warning</div>
<div class="content"><p>
<p>In a future release, a bad type for the <span class="code">Filename</span>
argument will probably generate an exception.</p>
<p></p>
</p></div>
</div>
</p></div>
<p><a name="sync-1"><span class="bold_code">sync(IoDevice) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">IoDevice = io_device()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Makes sure that any buffers kept by the operating system
(not by the Erlang runtime system) are written to disk. On
some platforms, this function might have no effect.</p>
<p>Typical error reasons are:</p>
<dl>
<dt><strong><span class="code">enospc</span></strong></dt>
<dd>
<p>Not enough space left to write the file.</p>
</dd>
</dl>
</p></div>
<p><a name="truncate-1"><span class="bold_code">truncate(IoDevice) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">IoDevice = io_device()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Truncates the file referenced by <span class="code">IoDevice</span> at
the current position. Returns <span class="code">ok</span> if successful,
otherwise <span class="code">{error, Reason}</span>.</p>
</p></div>
<p><a name="write-2"><span class="bold_code">write(IoDevice, Bytes) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">IoDevice = io_device()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Bytes = iodata()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Writes <span class="code">Bytes</span> to the file referenced by
<span class="code">IoDevice</span>. This function is the only way to write to a
file opened in raw mode (although it works for normally
opened files, too). Returns <span class="code">ok</span> if successful, and
<span class="code">{error, Reason}</span> otherwise.</p>
<p>If the file is opened with <span class="code">encoding</span> set to something else than <span class="code">latin1</span>, each byte written might result in several bytes actually being written to the file, as the byte range 0..255 might represent anything between one and four bytes depending on value and UTF encoding type.</p>
<p>Typical error reasons are:</p>
<dl>
<dt><strong><span class="code">ebadf</span></strong></dt>
<dd>
<p>The file is not opened for writing.</p>
</dd>
<dt><strong><span class="code">enospc</span></strong></dt>
<dd>
<p>There is a no space left on the device.</p>
</dd>
</dl>
</p></div>
<p><a name="write_file-2"><span class="bold_code">write_file(Filename, Bytes) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Bytes = iodata()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated | system_limit</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Writes the contents of the iodata term <span class="code">Bytes</span> to the
file <span class="code">Filename</span>. The file is created if it does not
exist. If it exists, the previous contents are
overwritten. Returns <span class="code">ok</span>, or <span class="code">{error, Reason}</span>.</p>
<p>Typical error reasons are:</p>
<dl>
<dt><strong><span class="code">enoent</span></strong></dt>
<dd>
<p>A component of the file name does not exist.</p>
</dd>
<dt><strong><span class="code">enotdir</span></strong></dt>
<dd>
<p>A component of the file name is not a directory. On some
platforms, <span class="code">enoent</span> is returned instead.</p>
</dd>
<dt><strong><span class="code">enospc</span></strong></dt>
<dd>
<p>There is a no space left on the device.</p>
</dd>
<dt><strong><span class="code">eacces</span></strong></dt>
<dd>
<p>Missing permission for writing the file or searching one
of the parent directories.</p>
</dd>
<dt><strong><span class="code">eisdir</span></strong></dt>
<dd>
<p>The named file is a directory.</p>
</dd>
</dl>
</p></div>
<p><a name="write_file-3"><span class="bold_code">write_file(Filename, Bytes, Modes) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Bytes = iodata()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Modes = [Mode] -- see open/2</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix() | terminated | system_limit</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Same as <span class="code">write_file/2</span>, but takes a third argument
<span class="code">Modes</span>, a list of possible modes, see
<span class="bold_code"><a href="#open-2">open/2</a></span>. The mode flags
<span class="code">binary</span> and <span class="code">write</span> are implicit, so they should
not be used.</p>
</p></div>
<p><a name="write_file_info-2"><span class="bold_code">write_file_info(Filename, FileInfo) -> ok | {error, Reason}</span></a><br></p>
<div class="REFBODY">
<p>Types:</p>
<div class="REFTYPES">
<span class="bold_code">Filename = name()</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">FileInfo = #file_info{} -- see also read_file_info/1</span><br>
</div>
<div class="REFTYPES">
<span class="bold_code">Reason = ext_posix()</span><br>
</div>
</div>
<div class="REFBODY"><p>
<p>Change file information. Returns <span class="code">ok</span> if successful,
otherwise <span class="code">{error, Reason}</span>. <span class="code">FileInfo</span> is a record
<span class="code">file_info</span>, defined in the Kernel include file
<span class="code">file.hrl</span>. Include the following directive in the module
from which the function is called:</p>
<div class="example"><pre>
-include_lib("kernel/include/file.hrl").</pre></div>
<p>The following fields are used from the record, if they are
given.</p>
<dl>
<dt><strong><span class="code">atime = time()</span></strong></dt>
<dd>
<p>The last (local) time the file was read.</p>
</dd>
<dt><strong><span class="code">mtime = time()</span></strong></dt>
<dd>
<p>The last (local) time the file was written.</p>
</dd>
<dt><strong><span class="code">ctime = time()</span></strong></dt>
<dd>
<p>On Unix, any value give for this field will be ignored
(the "ctime" for the file will be set to the current
time). On Windows, this field is the new creation time to
set for the file.</p>
</dd>
<dt><strong><span class="code">mode = int()</span></strong></dt>
<dd>
<p>The file permissions as the sum of the following bit
values:</p>
<dl>
<dt><strong>8#00400</strong></dt>
<dd>read permission: owner</dd>
<dt><strong>8#00200</strong></dt>
<dd>write permission: owner</dd>
<dt><strong>8#00100</strong></dt>
<dd>execute permission: owner</dd>
<dt><strong>8#00040</strong></dt>
<dd>read permission: group</dd>
<dt><strong>8#00020</strong></dt>
<dd>write permission: group</dd>
<dt><strong>8#00010</strong></dt>
<dd>execute permission: group</dd>
<dt><strong>8#00004</strong></dt>
<dd>read permission: other</dd>
<dt><strong>8#00002</strong></dt>
<dd>write permission: other</dd>
<dt><strong>8#00001</strong></dt>
<dd>execute permission: other</dd>
<dt><strong>16#800</strong></dt>
<dd>set user id on execution</dd>
<dt><strong>16#400</strong></dt>
<dd>set group id on execution</dd>
</dl>
<p>On Unix platforms, other bits than those listed above
may be set.</p>
</dd>
<dt><strong><span class="code">uid = int()</span></strong></dt>
<dd>
<p>Indicates the owner of the file. Ignored for non-Unix
file systems.</p>
</dd>
<dt><strong><span class="code">gid = int()</span></strong></dt>
<dd>
<p>Gives the group that the owner of the file belongs to.
Ignored non-Unix file systems.</p>
</dd>
</dl>
<p>Typical error reasons:</p>
<dl>
<dt><strong><span class="code">eacces</span></strong></dt>
<dd>
<p>Missing search permission for one of the parent
directories of the file.</p>
</dd>
<dt><strong><span class="code">enoent</span></strong></dt>
<dd>
<p>The file does not exist.</p>
</dd>
<dt><strong><span class="code">enotdir</span></strong></dt>
<dd>
<p>A component of the file name is not a directory. On some
platforms, <span class="code">enoent</span> is returned instead.</p>
</dd>
</dl>
</p></div>
<h3><a name="id2318688">POSIX Error Codes</a></h3>
<div class="REFBODY">
<ul>
<li>
<span class="code">eacces</span> - permission denied</li>
<li>
<span class="code">eagain</span> - resource temporarily unavailable</li>
<li>
<span class="code">ebadf</span> - bad file number</li>
<li>
<span class="code">ebusy</span> - file busy</li>
<li>
<span class="code">edquot</span> - disk quota exceeded</li>
<li>
<span class="code">eexist</span> - file already exists</li>
<li>
<span class="code">efault</span> - bad address in system call argument</li>
<li>
<span class="code">efbig</span> - file too large</li>
<li>
<span class="code">eintr</span> - interrupted system call</li>
<li>
<span class="code">einval</span> - invalid argument</li>
<li>
<span class="code">eio</span> - IO error</li>
<li>
<span class="code">eisdir</span> - illegal operation on a directory</li>
<li>
<span class="code">eloop</span> - too many levels of symbolic links</li>
<li>
<span class="code">emfile</span> - too many open files</li>
<li>
<span class="code">emlink</span> - too many links</li>
<li>
<span class="code">enametoolong</span> - file name too long</li>
<li>
<span class="code">enfile</span> - file table overflow</li>
<li>
<span class="code">enodev</span> - no such device</li>
<li>
<span class="code">enoent</span> - no such file or directory</li>
<li>
<span class="code">enomem</span> - not enough memory</li>
<li>
<span class="code">enospc</span> - no space left on device</li>
<li>
<span class="code">enotblk</span> - block device required</li>
<li>
<span class="code">enotdir</span> - not a directory</li>
<li>
<span class="code">enotsup</span> - operation not supported</li>
<li>
<span class="code">enxio</span> - no such device or address</li>
<li>
<span class="code">eperm</span> - not owner</li>
<li>
<span class="code">epipe</span> - broken pipe</li>
<li>
<span class="code">erofs</span> - read-only file system</li>
<li>
<span class="code">espipe</span> - invalid seek</li>
<li>
<span class="code">esrch</span> - no such process</li>
<li>
<span class="code">estale</span> - stale remote file handle</li>
<li>
<span class="code">exdev</span> - cross-domain link</li>
</ul>
</div>
<h3><a name="id2318906">Performance</a></h3>
<div class="REFBODY">
<p>Some operating system file operations, for example a
<span class="code">sync/1</span> or <span class="code">close/1</span> on a huge file, may block their
calling thread for seconds. If this befalls the emulator main
thread, the response time is no longer in the order of
milliseconds, depending on the definition of "soft" in soft
real-time system.</p>
<p>If the device driver thread pool is active, file operations are
done through those threads instead, so the emulator can go on
executing Erlang processes. Unfortunately, the time for serving a
file operation increases due to the extra scheduling required
from the operating system.</p>
<p>If the device driver thread pool is disabled or of size 0, large
file reads and writes are segmented into several smaller, which
enables the emulator so server other processes during the file
operation. This gives the same effect as when using the thread
pool, but with larger overhead. Other file operations, for
example <span class="code">sync/1</span> or <span class="code">close/1</span> on a huge file, still are
a problem.</p>
<p>For increased performance, raw files are recommended. Raw files
uses the file system of the node's host machine. For normal files
(non-raw), the file server is used to find the files, and if
the node is running its file server as slave to another node's,
and the other node runs on some other host machine, they may have
different file systems. This is seldom a problem, but you have
now been warned.</p>
<p>A normal file is really a process so it can be used as an IO
device (see <span class="code">io</span>). Therefore when data is written to a
normal file, the sending of the data to the file process, copies
all data that are not binaries. Opening the file in binary mode
and writing binaries is therefore recommended. If the file is
opened on another node, or if the file server runs as slave to
another node's, also binaries are copied.</p>
<p>Caching data to reduce the number of file operations, or rather
the number of calls to the file driver, will generally increase
performance. The following function writes 4 MBytes in 23
seconds when tested:</p>
<div class="example"><pre>
create_file_slow(Name, N) when integer(N), N >= 0 ->
{ok, FD} = file:open(Name, [raw, write, delayed_write, binary]),
ok = create_file_slow(FD, 0, N),
ok = ?FILE_MODULE:close(FD),
ok.
create_file_slow(FD, M, M) ->
ok;
create_file_slow(FD, M, N) ->
ok = file:write(FD, <<M:32/unsigned>>),
create_file_slow(FD, M+1, N).</pre></div>
<p>The following, functionally equivalent, function collects 1024
entries into a list of 128 32-byte binaries before each call to
<span class="code">file:write/2</span> and so does the same work in 0.52 seconds,
which is 44 times faster.</p>
<div class="example"><pre>
create_file(Name, N) when integer(N), N >= 0 ->
{ok, FD} = file:open(Name, [raw, write, delayed_write, binary]),
ok = create_file(FD, 0, N),
ok = ?FILE_MODULE:close(FD),
ok.
create_file(FD, M, M) ->
ok;
create_file(FD, M, N) when M + 1024 =&lt; N ->
create_file(FD, M, M + 1024, []),
create_file(FD, M + 1024, N);
create_file(FD, M, N) ->
create_file(FD, M, N, []).
create_file(FD, M, M, R) ->
ok = file:write(FD, R);
create_file(FD, M, N0, R) when M + 8 =&lt; N0 ->
N1 = N0-1, N2 = N0-2, N3 = N0-3, N4 = N0-4,
N5 = N0-5, N6 = N0-6, N7 = N0-7, N8 = N0-8,
create_file(FD, M, N8,
[<<N8:32/unsigned, N7:32/unsigned,
N6:32/unsigned, N5:32/unsigned,
N4:32/unsigned, N3:32/unsigned,
N2:32/unsigned, N1:32/unsigned>> | R]);
create_file(FD, M, N0, R) ->
N1 = N0-1,
create_file(FD, M, N1, [<<N1:32/unsigned>> | R]).</pre></div>
<div class="note">
<div class="label">Note</div>
<div class="content"><p>
<p>Trust only your own benchmarks. If the list length in
<span class="code">create_file/2</span> above is increased, it will run slightly
faster, but consume more memory and cause more memory
fragmentation. How much this affects your application is
something that this simple benchmark can not predict.</p>
<p>If the size of each binary is increased to 64 bytes, it will
also run slightly faster, but the code will be twice as clumsy.
In the current implementation are binaries larger than 64 bytes
stored in memory common to all processes and not copied when
sent between processes, while these smaller binaries are stored
on the process heap and copied when sent like any other term.</p>
<p>So, with a binary size of 68 bytes <span class="code">create_file/2</span> runs
30 percent slower then with 64 bytes, and will cause much more
memory fragmentation. Note that if the binaries were to be sent
between processes (for example a non-raw file) the results
would probably be completely different.</p>
</p></div>
</div>
<p>A raw file is really a port. When writing data to a port, it is
efficient to write a list of binaries. There is no need to
flatten a deep list before writing. On Unix hosts, scatter output,
which writes a set of buffers in one operation, is used when
possible. In this way <span class="code">file:write(FD, [Bin1, Bin2 | Bin3])</span>
will write the contents of the binaries without copying the data
at all except for perhaps deep down in the operating system
kernel.</p>
<p>For raw files, <span class="code">pwrite/2</span> and <span class="code">pread/2</span> are
efficiently implemented. The file driver is called only once for
the whole operation, and the list iteration is done in the file
driver.</p>
<p>The options <span class="code">delayed_write</span> and <span class="code">read_ahead</span> to
<span class="code">file:open/2</span> makes the file driver cache data to reduce
the number of operating system calls. The function
<span class="code">create_file/2</span> in the example above takes 60 seconds
seconds without the <span class="code">delayed_write</span> option, which is 2.6
times slower.</p>
<p>And, as a really bad example, <span class="code">create_file_slow/2</span> above
without the <span class="code">raw</span>, <span class="code">binary</span> and <span class="code">delayed_write</span>
options, that is it calls <span class="code">file:open(Name, [write])</span>, needs
1 min 20 seconds for the job, which is 3.5 times slower than
the first example, and 150 times slower than the optimized
<span class="code">create_file/2</span>. </p>
</div>
<h3><a name="id2319157">Warnings</a></h3>
<div class="REFBODY">
<p>If an error occurs when accessing an open file with the <span class="code">io</span>
module, the process which handles the file will exit. The dead
file process might hang if a process tries to access it later.
This will be fixed in a future release.</p>
</div>
<h3><a name="id2319176">SEE ALSO</a></h3>
<div class="REFBODY">
<p><span class="bold_code"><a href="javascript:erlhref('../../../../doc/../','stdlib','filename.html');">filename(3)</a></span></p>
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by-pkgid
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f806c0f24240b25bde21a53f71766070
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