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<h1 align=center>NCDUMP</h1>
<a href="#NAME">NAME</a><br>
<a href="#SYNOPSIS">SYNOPSIS</a><br>
<a href="#DESCRIPTION">DESCRIPTION</a><br>
<a href="#OPTIONS">OPTIONS</a><br>
<a href="#EXAMPLES">EXAMPLES</a><br>
<a href="#REFERENCES">REFERENCES</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
<a href="#BUGS">BUGS</a><br>
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<a name="NAME"></a>
<h2>NAME</h2>
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<p>ncdump − Convert netCDF file to text form (CDL)</p>
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<a name="SYNOPSIS"></a>
<h2>SYNOPSIS</h2>
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<p>ncdump [-c] [-h] [-v <i>var1,...</i>] [-b <i>lang</i>]
[-f <i>lang</i>] [-l <i>len</i>] [-n <i>name</i>] [-p
<i>f_digits[,d_digits]</i>] [-k] [-x] [-s] [-t]
<i>file</i></p>
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<a name="DESCRIPTION"></a>
<h2>DESCRIPTION</h2>
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<p><b>ncdump</b> generates a text representation of a
specified netCDF file on standard output. The text
representation is in a form called CDL
(‘‘network Common Data form
Language’’) that can be viewed, edited, or serve
as input to <b>ncgen</b>. <b>ncgen</b> is a companion
program that can generate a binary netCDF file from a CDL
file. Hence <b>ncgen</b> and <b>ncdump</b> can be used as
inverses to transform the data representation between binary
and text representations. See <b>ncgen</b> for a description
of CDL and netCDF representations.</p>
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<p>As of NetCDF version 4.1, and if DAP support was enabled
when <b>ncdump</b> was built, the file name may specify a
DAP URL. This allows <b>ncdump</b> to print out data sources
from DAP servers. When used with the <b>-h</b> option,
<b>ncdump</b> can be used to show the translation from the
DAP DDS data model to the NetCDF data model.</p>
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<p><b>ncdump</b> defines a default display format used for
each type of netCDF data, but this can be changed if a
‘C_format’ attribute is defined for a netCDF
variable. In this case, <b>ncdump</b> will use the
‘C_format’ attribute to format each value. For
example, if floating-point data for the netCDF variable
‘Z’ is known to be accurate to only three
significant digits, it would be appropriate to use the
variable attribute</p></td>
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<p>Z:C_format = "%.3g"</p></td>
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<p><b>ncdump</b> may also be used as a simple browser for
netCDF data files, to display the dimension names and sizes;
variable names, types, and shapes; attribute names and
values; and optionally, the values of data for all variables
or selected variables in a netCDF file.</p>
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<p><b>ncdump</b> uses ‘_’ to represent data
values that are equal to the ‘_FillValue’
attribute for a variable, intended to represent data that
has not yet been written. If a variable has no
‘_FillValue’ attribute, the default fill value
for the variable type is used if the variable is not of byte
type.</p>
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<p><b>ncdump</b> may also be used to determine what kind of
netCDF file is used (which variant of the netCDF file
format) with the -k option.</p>
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<a name="OPTIONS"></a>
<h2>OPTIONS</h2>
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<p><b>-c</b></p>
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<p>Show the values of <i>coordinate</i> variables
(variables that are also dimensions) as well as the
declarations of all dimensions, variables, and attribute
values. Data values of non-coordinate variables are not
included in the output. This is the most suitable option to
use for a brief look at the structure and contents of a
netCDF file.</p>
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<p><b>-h</b></p>
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<p>Show only the <i>header</i> information in the output,
that is the declarations of dimensions, variables, and
attributes but no data values for any variables. The output
is identical to using the <b>-c</b> option except that the
values of coordinate variables are not included. (At most
one of <b>-c</b> or <b>-h</b> options may be present.)</p>
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<p><b>-v</b> <i>var1,...,varn</i></p></td>
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<p>The output will include data values for the specified
variables, in addition to the declarations of all
dimensions, variables, and attributes. One or more variables
must be specified by name in the comma-delimited list
following this option. The list must be a single argument to
the command, hence cannot contain blanks or other white
space characters unless escaped. The named variables must be
valid netCDF variables in the input-file. A variable within
a group in a netCDF-4 file may be specified with an absolute
pathname, such as ‘/GroupA/GroupA2/var’. Use of
a relative pathname such as ‘var’ or
‘grp/var’ specifies all matching variable names
in the file. The default, without this option and in the
absence of the <b>-c</b> or <b>-h</b> options, is to include
data values for <i>all</i> variables in the output.</p>
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<p><b>-b</b> <i>lang</i></p></td>
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<p>A brief annotation in the form of a CDL comment (text
beginning with the characters
‘‘//’’) will be included in the data
section of the output for each ‘row’ of data, to
help identify data values for multidimensional variables. If
<i>lang</i> begins with ‘C’ or ‘c’,
then C language conventions will be used (zero-based
indices, last dimension varying fastest). If <i>lang</i>
begins with ‘F’ or ‘f’, then Fortran
language conventions will be used (one-based indices, first
dimension varying fastest). In either case, the data will be
presented in the same order; only the annotations will
differ. This option is useful for browsing through large
volumes of multidimensional data.</p>
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<p><b>-f</b> <i>lang</i></p></td>
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<p>Full annotations in the form of trailing CDL comments
(text beginning with the characters
‘‘//’’) for every data value (except
individual characters in character arrays) will be included
in the data section. If <i>lang</i> begins with
‘C’ or ‘c’, then C language
conventions will be used (zero-based indices, last dimension
varying fastest). If <i>lang</i> begins with ‘F’
or ‘f’, then Fortran language conventions will
be used (one-based indices, first dimension varying
fastest). In either case, the data will be presented in the
same order; only the annotations will differ. This option
may be useful for piping data into other filters, since each
data value appears on a separate line, fully identified.</p>
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<p><b>-l</b> <i>len</i></p>
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<p>Changes the default maximum line length (80) used in
formatting lists of non-character data values.</p>
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<p><b>-n</b> <i>name</i></p></td>
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<p>CDL requires a name for a netCDF data set, for use by
<b>ncgen -b</b> in generating a default netCDF file name. By
default, <i>ncdump</i> constructs this name from the last
component of the pathname of the input netCDF file by
stripping off any extension it has. Use the <b>-n</b> option
to specify a different name. Although the output file name
used by <b>ncgen -b</b> can be specified, it may be wise to
have <i>ncdump</i> change the default name to avoid
inadvertantly overwriting a valuable netCDF file when using
<b>ncdump</b>, editing the resulting CDL file, and using
<b>ncgen -b</b> to generate a new netCDF file from the
edited CDL file.</p>
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<p><b>-p</b> <i>float_digits[,double_digits]</i></p></td>
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<p>Specifies default precision (number of significant
digits) to use in displaying floating-point or double
precision data values for attributes and variables. If
specified, this value overrides the value of the
‘C_format’ attribute for any variable that has
such an attribute. Floating-point data will be displayed
with <i>float_digits</i> significant digits. If
<i>double_digits</i> is also specified, double-precision
values will be displayed with that many significant digits.
In the absence of any <b>-p</b> specifications,
floating-point and double-precision data are displayed with
7 and 15 significant digits respectively. CDL files can be
made smaller if less precision is required. If both
floating-point and double-presision precisions are
specified, the two values must appear separated by a comma
(no blanks) as a single argument to the command. If you
really want every last bit of precision from the netCDF file
represented in the CDL file for all possible floating-point
values, you will have to specify this with <b>-p 9,17</b>
(according to Theorem 15 of the paper listed under
REFERENCES).</p>
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<p><b>-k</b></p>
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<p>Show what kind of netCDF file the pathname references,
one of ‘classic’, ‘64-bit
offset’,‘netCDF-4’, or ‘netCDF-4
classic model’. Before version 3.6, there was only one
kind of netCDF file, designated as ‘classic’
(also know as format variant 1). Large file support
introduced another variant of the format, designated as
‘64-bit offset’ (known as format variant 2).
NetCDF-4, uses a third variant of the format,
‘netCDF-4’ (format variant 3). Another format
variant, designated ‘netCDF-4 classic model’
(format variant 4), is restricted to features supported by
the netCDF-3 data model but represented using the HDF5
format, so that an unmodified netCDF-3 program can read or
write the file just by relinking with the netCDF-4 library.
The string output by using the ‘-k’ option may
be provided as the value of the ‘-k’ option to
ncgen(1) to specify exactly what kind of netCDF file to
generate, when you want to override the default inferred
from the CDL.</p>
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<p><b>-x</b></p>
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<p>Output XML (NcML) instead of CDL. The NcML does not
include data values. The NcML output option doesn’t
yet display netCDF-4 data correctly.</p>
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<p><b>-s</b></p>
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<p>Output special virtual attributes that provide
performance-related information about the file format and
variable properties for netCDF-4 data. These special virtual
attributes are not actually part of the data, they are
merely a convenient way to display miscellaneous properties
of the data in CDL (and eventually NcML). They include
‘_ChunkSizes’, ‘_DeflateLevel’,
‘_Endianness’, ‘_Fletcher32’,
‘_Format’, ‘_NoFill’,
‘_Shuffle’, and ‘_Storage’.
‘_ChunkSizes’ is a list of chunk sizes for each
dimension of the variable. ‘_DeflateLevel’ is an
integer between 0 and 9 inclusive if compression has been
specified for the variable. ‘_Endianness’ is
either ‘little’ or ‘big’, depending
on how the variable was stored when first written.
‘_Fletcher32’ is ‘true’ if the
checksum property was set for the variable.
‘_Format’ is a global attribute specifying the
netCDF format variant, one of ‘classic’,
‘64-bit offset’, ‘netCDF-4’, or
‘netCDF-4 classic model’. ‘_NoFill’
is ‘true’ if the persistent NoFill property was
set for the variable when it was defined.
‘_Shuffle’ is ‘true’ if use of the
shuffle filter was specified for the variable.
‘_Storage’ is ‘contiguous’ or
‘chunked’, depending on how the variable’s
data is stored.</p>
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<p><b>-t</b></p>
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<p>Controls display of time data, if stored in a variable
that uses a udunits compliant time representation such as
‘days since 1970-01-01’ or ‘seconds since
2009-03-15 12:01:17’. If this option is specified,
time values are displayed as human-readable date-time
strings rather than numerical values, interpreted in terms
of a ‘calendar’ variable attribute, if
specified. Calendar attribute values interpreted with this
option include the CF Conventions values
‘gregorian’ or ‘standard’,
‘proleptic_gregorian’, ‘noleap’ or
‘365_day’, ‘all_leap’ or
‘366_day’, ‘360_day’, or
‘julian’.</p>
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<a name="EXAMPLES"></a>
<h2>EXAMPLES</h2>
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<p>Look at the structure of the data in the netCDF file
‘<b>foo.nc</b>’:</p></td>
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<p>ncdump -c foo.nc</p></td>
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<p>Produce an annotated CDL version of the structure and
data in the netCDF file ‘<b>foo.nc</b>’, using
C-style indexing for the annotations:</p></td>
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<p>ncdump -b c foo.nc > foo.cdl</p></td>
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<p>Output data for only the variables ‘uwind’
and ‘vwind’ from the netCDF file
‘<b>foo.nc</b>’, and show the floating-point
data with only three significant digits of
precision:</p></td>
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<p>ncdump -v uwind,vwind -p 3 foo.nc</p></td>
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<p>Produce a fully-annotated (one data value per line)
listing of the data for the variable ‘omega’,
using Fortran conventions for indices, and changing the
netCDF dataset name in the resulting CDL file to
‘omega’:</p></td>
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<p>ncdump -v omega -f fortran -n omega foo.nc >
Z.cdl</p></td>
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<a name="REFERENCES"></a>
<h2>REFERENCES</h2>
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<p><i>What Every Computer Scientist should Know About
Floating-Point Arithmetic</i>, D. Goldberg, <b>ACM Computing
Surveys, Vol. 23, No. 1</b>, March 1991, pp. 5-48. Climate
and Forecast Metadata Conventions,
http://www.cfconventions.org.</p>
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<a name="SEE ALSO"></a>
<h2>SEE ALSO</h2>
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<p><b>ncgen</b>(1), <b>netcdf</b>(3)</p>
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<a name="BUGS"></a>
<h2>BUGS</h2>
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<p>Character arrays that contain a null-byte are treated
like C strings, so no characters after the null byte appear
in the output.</p>
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<p>Multidimensional character string arrays are not handled
well, since the CDL syntax for breaking a long character
string into several shorter lines is weak.</p>
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<p>There should be a way to specify that the data should be
displayed in ‘record’ order, that is with the
all the values for ‘record’ variables together
that have the same value of the record dimension.</p>
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