ncmpidump - Convert netCDF files to ASCII form (CDL)

       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.

Printed: 2025-07-29                      PnetCDF PNETCDF_RELEASE_VERSION                            ncmpidump(1)

       PNETCDF_RELEASE_DATE

ncmpidump  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,  edit‐
       ed,  or  serve  as  input to ncmpigen.  ncmpigen is a companion program that can generate a binary netCDF
       file from a CDL file.  Hence ncmpigen and ncmpidump can be used as inverses to transform the data  repre‐
       sentation  between  binary  and  ASCII representations.  See ncmpigen for a description of CDL and netCDF
       representations.

       ncmpidump may also be used to determine what kind of netCDF file is used (which  variant  of  the  netCDF
       file format) with the -k option.

       ncmpidump  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, ncmpidump 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"

       ncmpidump  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.

       ncmpidump  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.

       Look at the structure of the data in the netCDF file `foo.nc':

              ncmpidump -c foo.nc

       Produce an annotated CDL version of the structure and data in the netCDF file `foo.nc', using C-style in‐
       dexing for the annotations:

              ncmpidump -b c foo.nc > foo.cdl

       Output data for only the variables `uwind' and `vwind' from the netCDF file `foo.nc', and show the float‐
       ing-point data with only three significant digits of precision:

              ncmpidump -v uwind,vwind -p 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':

              ncmpidump -v omega -f fortran -n omega foo.nc > Z.cdl

       ncmpidump - Convert netCDF files to ASCII form (CDL)

-c     Show the values of coordinate variables (variables that are also dimensions) as well as the decla‐
              rations  of  all dimensions, variables, and attribute values.  Data values of non-coordinate vari‐
              ables 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  op‐
              tion  except  that  the values of coordinate variables are not included.  (At most one of -c or -h
              options may be present.)

       -vvar1,...,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  com‐
              mand,  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.

       -blang
              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.

       -flang
              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 lan‐
              guage 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.

       -llen Changes the default maximum line length (80) used in formatting lists of non-character  data  val‐
              ues.

       -nname
              CDL  requires  a name for a netCDF data set, for use by ncmpigen-b in generating a default netCDF
              file name.  By default, ncmpidump 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 dif‐
              ferent name.  Although the output file name used by ncmpigen-b can be specified, it may  be  wise
              to  have  ncmpidump  change  the default name to avoid inadvertantly overwriting a valuable netCDF
              file when using ncmpidump, editing the resulting CDL file, and using ncmpigen-b to generate a new
              netCDF file from the edited CDL file.

       -pfloat_digits[,double_digits]
              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 da‐
              ta  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.  In  the  absence  of
              any  -p  specifications, floating-point and double-precision data are displayed with 7 and 15 sig‐
              nificant digits respectively.  CDL files can be made smaller if less precision  is  required.   If
              both floating-point and double-precision precisions are specified, the two values must appear sep‐
              arated  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 -p9,17 (according to Theorem 15 of the paper listed
              under REFERENCES).

       -k     Reports the kind of netCDF file: classic, 64-bit offset, or 64-bit data.   Before  netCDF  version
              3.6,  there was only one kind of netCDF file, designated as `classic' (also know as format variant
              1 or CDF-1).  Large file support introduced another variant of the format, designated  as  `64-bit
              offset'  (known  as  format variant 2 or CDF-2).  Large data support introduced another variant of
              the format, designated as `64-bit data' (known as format variant 5 or CDF-5).

WhatEveryComputerScientistshouldKnowAboutFloating-PointArithmetic, D.  Goldberg,  ACMComputingSurveys,Vol.23,No.1, March 1991, pp. 5-48.

ncmpigen(1), pnetcdf(3)

       ncmpidump [-ch] [-v var1,...]  [-b lang] [-f lang] [-l len] [-n name] [-p f_digits[,d_digits]] file

       ncmpidump -k file