NAME

       cdfdiff - compares two classic netCDF files in parallel

SYNOPSIS

       cdfdiff [-b] [-q] [-h] [-v var1,...,varn] [-t diff,ratio] file1 file2

DESCRIPTION

       cdfdiff,  a  sequential  version  of  ncmpidiff,  compares the contents of the two classic
       netCDF files and reports the first difference found to the standard  output.  The  classic
       file formats include CDF-1, CDF-2, and CDF-5.

       For  variables  and  attributes,  it  reports the array indices of the first element found
       different when option -t is not used. When option -t is used, it reports the element  with
       the largest difference that fails to meet the tolerance requirements.

       If  neither  argument  -v nor -h is given besides the two file names, the entire files are
       compared.

       When comparing two files entirely, the difference between cdfdiff  and  the  Unix  command
       diff  is  that  cdfdiff  skips  the  gaps  between  variables. The gaps may occur when the
       alignment feature is used to create a new file. This alignment allows to allocate a larger
       space for the file header and align the starting file offsets of fixed-size variables (see
       API ncmpi__enddef and PnetCDF hints).  Oftentimes,  the  contents  of  gaps  are  non-zero
       arbitrary  bytes.  Thus,  two  netCDF  files  (of same or different sizes) can be reported
       identical by cdfdiff but not by diff.

OPTIONS

       -b     Verbose mode - print results (same or different) for all components (file,  header,
              or variables) in comparison

       -q     Quiet  mode  - print nothing on the command-line output. This also disables verbose
              mode. When in quiet mode, users should  check  exit  status.  See  below  in  "EXIT
              STATUS".

       -h     Compare file header only

       -v var1,...,varn
              Compare only the given list of variables (names separated by comma without space).

       -t diff,ratio
              Compare  variables element-wisely with tolerance (diff and ratio separated by comma
              without space).  diff is the absolute value  of  element-wise  difference  of   two
              variables  with  the  same  name  but  stored in the two input files.  ratio is the
              relative element-wise difference ratio defined as |x - y|/max(|x|, |y|), where x is
              an array element from a variable in the first file and y is the corresponding array
              element of the same variable in the second file. |x| represents the absolute  value
              of  x.  Note  when  this  option  is  used, the output reports only the first array
              element that fails to meet both tolerance requirements.

EXIT STATUS

       An exit status of 0 means no differences were found, and 1  means  some  differences  were
       found.  Note on VMS-based system, the exit status values are reversed.

SEE ALSO

       ncmpidiff(1), ncmpidump(1), diff(1), pnetcdf(3)

DATE

       February 21, 2022