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SYNOPSIS
ncdump [-c] [-h] [-v var1,...] [-b lang] [-f lang] [-l len] [-n name] [-d
f_digits[,d_digits]] file
DESCRIPTION
ncdump generates an ASCII representation of a specified netCDF file on
standard output. The ASCII representation is in a form called CDL
(``network Common Data form Language'') that can be viewed, edited, or
serve as input to ncgen. ncgen is a companion program that can generate
a binary netCDF file from a CDL file. Hence ncgen and ncdump can be used
as inverses to transform the data representation between binary and ASCII
representations. See ncgen for a description of CDL and netCDF
representations.
ncdump 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, ncdump 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
Z:C_format = "%.3g"
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.
OPTIONS
-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 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 the
declarations of dimensions, variables, and attributes 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,...,varn
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
-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.
-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.
-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 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 -d specifications, floating-point and double-precision data
are displayed with 7 and 15 significant digits respectively. CDL
precision from the netCDF file represented in the CDL file for all
possible floating-point values, you will have to specify this with
-d 9,17 (according to Theorem 15 of the paper listed under
REFERENCES).
EXAMPLES
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
REFERENCES
What Every Computer Scientist should Know About Floating-Point
Arithmetic, D. Goldberg, ACM Computing Surveys, Vol. 23, No. 1, March
1991, pp. 5-48.
SEE ALSO
ncgen(1), netcdf(3)
BUGS
Character arrays that contain a null-byte are treated like C strings, so
no characters after the null byte appear in the output.
Multidimensional character string arrays are not handled well, since the
CDL syntax for breaking a long character string into several shorter
lines is weak.
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.