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The ncdump
tool generates an ASCII representation of a netCDF
file on standard output, either with or without an ASCII representation
of the variable data in the file. The ASCII representation used is the
CDL notation that ncgen
accepts as input. Thus ncdump
and
ncgen
can be used as inverses to transform data representation
between binary and ASCII representations.
ncdump
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.
ncdump
defines a default format used for each type of netCDF
variable data, but this can be overridden if a C_format
attribute is
defined for a netCDF variable. In this case, ncdump
will use the
C_format
attribute to format values for that variable. 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
Z:C_format = "%.3g"
UNIX syntax for invoking ncdump
:
ncdump [ -c | -h] [-v var1,...] [-b lang] [-f lang]
[-l len] [ -d fdig[,ddig]] [ -n name] [input-file]
where:
- `-c'
- Show the values of coordinate 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 often
the most suitable option to use for a brief look at the structure and
contents of a netCDF file.
- `-h'
- Show only the header information in the output, that is, output
only the declarations for the netCDF dimensions, variables, and
attributes of the input file, but no data values for any variables. The
output is identical to using the `-c' option except that the values
of coordinate variables are not included. (At most one of `-c' or
`-h' options may be present.)
- `-v var1,...'
- 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 `-c' or `-h' options, is to include data values for all
variables in the output.
- `-b lang'
- 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 lang begins with `C' or
`c', then C language conventions will be used (zero-based indices,
last dimension varying fastest). If lang 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.
- `-f lang'
- 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 lang begins with `C' or `c', then C language
conventions will be used (zero-based indices, last dimension varying
fastest). If lang 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.
- `-l len'
- Changes the default maximum line length (80) used in formatting lists of
non-character data values.
- `-d float_digits[,double_digits]'
- 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
float_digits significant digits. If double_digits is also
specoified, 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
`-d' 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.
- `-n name'
- CDL requires a name for a netCDF data set, for use by `ncgen -b' in
generating a default netCDF file name. By default,
ncdump
constructs this name from the last component of the pathname of the
input netCDF file by stripping off any extension it has. Use the
`-n' option to specify a different name. Although the output file
name used by `ncgen -b' can be specified, it may be wise to have
ncdump
change the default name to avoid inadvertantly overwriting
a valuable netCDF file when using ncdump
, editing the resulting
CDL file, and using `ncgen -b' to generate a new netCDF file from
the edited CDL file.
Look at the structure of the data in the netCDF file `foo.nc':
ncdump -c foo.nc
Produce an annotated CDL version of the structure and data in the
netCDF file `foo.nc', using C-style indexing for the annotations:
ncdump -b c foo.nc > foo.cdl
Output data for only the variables uwind
and vwind
from
the netCDF file `foo.nc', and show the floating-point data with
only three significant digits of precision:
ncdump -v uwind,vwind -d 3 foo.nc
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
:
ncdump -v omega -f fortran -n omega foo.nc > Z.cdl
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