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<h2>ncdump</h2>
<code>ncdump [-c] [-h] [-v <i>var1</i>,...] [-b <i>lang</i>] [-f
<i>lang</i>] [-l <i>len</i>]
[-n <i>name</i>] [-d <i>f_digits</i>[,<i>d_digits</i>]]
<i>file</i></code><p>
Where:<p>
<ul>
<code>-c</code> 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>
<code>-h</code> 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 <code>-c</code> option except
that the
values of coordinate variables are not included. (At
most one of <code>-c</code> or <code>-h</code> options may be
present.) <p>
<code>-v</code>
<code><i>var1,...,varn</i></code><br>
<ul>
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. The named variables must
be valid netCDF variables in the input-file. The default, without this option and in the absence of the
<code>-c</code>
or <code>-h</code> options, is to include data values for
<i>all</i> variables in the output.</ul><p>
<code>-b <i>lang</i></code><br>
<ul>
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 <code><i>lang</i></code> begins with
<code>C</code> or <code>c</code>, then C
language conventions will be used (zero-based indices,
last dimension varying fastest). If <code><i>lang</i></code>
begins
with
<code>F</code> or <code>f</code>, 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. </ul><p>
<code>-f <i>lang</i></code><p>
<ul>
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
<code><i>lang</i></code>
begins with <code>C</code> or <code>c</code>, then C
language conventions
will be used (zero-based indices, last dimension varying
fastest). If <code><i>lang</i></code> begins with <code>F</code> or
<code>f</code>, 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.</ul><p>
<code>-l <i>len</i></code><br>
<ul>
Changes the default maximum line
length (80) used
in
formatting lists of non-character data values. </ul><p>
<code>-n <i>name</i></code><br>
<ul>
CDL requires a name for a netCDF data set, for use by
<a href="ncgen.html"><code>ncgen -b</code></a>
in generating a default netCDF file name. By
default, <code>ncdump</code> constructs this name from the
last component of the pathname of the input netCDF file by
stripping off any extension it has. Use the <code>-n</code>
option
to specify a different name. Although the output file
name used by <a href="ncgen.html"><code>ncgen -b</code></a>
can be specified, it may be wise
to have <code>ncdump</code> change the default name to avoid
inadvertantly overwriting a valuable netCDF file when using
<code>ncdump</code>, editing the resulting CDL file, and using
<a href="ncgen.html"><code>ncgen
-b</code></a> to generate a new netCDF file from the edited
CDL
file.</ul><p>
<code>-d <i>float_digits</i>[,</i>double_digits</i>]</code><p>
<ul>
Specifies default number of significant digits to use
in displaying floating-point or double precision data
values for variables that don't have a `C_format' attribute. Floating-point data will be displayed with
<code><i>float_digits</i></code> significant digits. If
<code><i>double_digits</i></code> is
also specified, double-precision values will be
displayed with that many significant digits. If a
variable has a `C_format' attribute, that overrides any
specified floating-point default. In the absence of
any <code>-d</code> 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 <code>-d
9,17</code>.</ul></ul>
<h3>Usage Notes</h3>
<code>ncdump</code> generates an ASCII representation of a
specified
netCDF file on standard output. The ASCII representation is
in a form called <code>CDL</code> (``network Common Data form
Language'')
that can be viewed, edited, or serve as input to <a
href="ncgen.html"><code>ncgen</code></a>.
<a href="ncgen.html"><code>ncgen</code></a> is a companion program
that can generate a binary
netCDF file from a <code>CDL</code> file. Hence <a
href="ncgen.html"><code>ncgen</code></a> and <code>ncdump</code> can
be
used as inverses to transform the data representation
between binary and ASCII representations. See <a
href="ncgen.html"><code>ncgen</code></a> for a
description of CDL and netCDF representations.<p>
<code>ncdump</code> defines a default 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, <code>ncdump</code>
will
use the `C_format' attribute to format each value. For example,
if floating-point data for the netCDF variable <code>Z</code> is
known to be accurate to only three significant digits, it
would be appropriate to use the variable attribute<p>
<dd><code>Z:C_format = "%.3g"</code><p>
<code>ncdump</code> 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>
<h3>Examples</h3>
<ol>
Look at the structure of the data in the netCDF file
<code>foo.nc</code>:<p>
<dd><code>ncdump -c foo.nc</code><p>
<li>Produce an annotated CDL version of the structure and data
in the netCDF file <code>foo.nc</code>, using C-style indexing for
the
annotations:<p>
<dd><code>ncdump -b c foo.nc > foo.cdl</code><p>
<li>Output data for only the variables <code>uwind</code> and
<code>vwind</code> from
the netCDF file <code>foo.nc</code>, and show the floating-point
data
with only three significant digits of precision:<p>
<dd><code>ncdump -v uwind,vwind -d 3 foo.nc</code><p>
<li>Produce a fully-annotated (one data value per line) listing
of the data for the variable <code>omega</code>, using Fortran
conventions for indices, and changing the netCDF dataset name in
the resulting CDL file to <code>omega</code>:<p>
<dd><code>ncdump -v omega -f fortran -n omega foo.nc > Z.cdl</code></ol>
