NAME¶

ncoffsets - print the starting/ending file offsets for netCDF variables

SYNOPSIS¶

ncoffsets [-h] | [-x] | [-sgr] [-v var1[,...]] file

DESCRIPTION¶

ncoffsets prints the file offsets information of variables defined in a given netCDF file. The ending offsets reported is an exclusive offset, i.e. 1 byte more than the last byte occupied by the variable. In other words, the ending offset is equal to the sum of starting offset and the variable size. For record variables, only the offsets of first record are printed. Add option -r to print the offsets of all records.

If no argument is given, command usage information is printed.

OPTIONS¶

-v var1[,...]

The output will include data values for the specified variables. 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 is to include data values for all variables in the output.

-s

Print the variable size in bytes. For record variables, only the size of one record is printed.

-g

Print the gap in bytes from the previous variable. For the first defined variable, print the gap from the end of file header. For record variables, there is no gap between records.

-r

Output the offset information for all records of the selected record variables. Without this option, only the offsets of first record are printed.

-x

Check all fixed-size variable for file space gaps in between any two immediately adjacent variables. It prints "1" on stdout if gaps are found, "0" for otherwise. This option disables all other options.

-h

Print the available command-line options

EXAMPLES¶

Print the file offset information for all variables in a netCDF file.

% ncoffsets -sg testfile.nc

netcdf testfile.nc {
//file format: CDF-1
file header:
	size   = 340 bytes
	extent = 340 bytes
dimensions:
	x = 100
	y = 100
	z = 100
	time = UNLIMITED // (100 currently)
fixed-size variables:
	double square(x, y):
	       start file offset =         340
	       end   file offset =       80340
	       size in bytes     =       80000
	       gap from prev var =           0
	double cube(x, y, z):
	       start file offset =       80340
	       end   file offset =     8080340
	       size in bytes     =     8000000
	       gap from prev var =           0
record variables:
	double time(time):
	       start file offset =     8080340    (record 0)
	       end   file offset =     8081140    (record 0)
	       size in bytes     =           8    (of one record)
	       gap from prev var =           0
	double xytime(time, x, y):
	       start file offset =     8080348    (record 0)
	       end   file offset =    16080348    (record 0)
	       size in bytes     =       80000    (of one record)
	       gap from prev var =           0
}

Check if there are gaps in between two adjacent fixed-size variables.
% ncoffsets -x testfile.nc
0

SEE ALSO¶

pnetcdf(3)

DATE¶

February 21, 2022