## Substitution of system commands in backquotes

Command-line substitution is specified by a system command enclosed in backquotes. This command is spawned and the output it produces replaces the backquoted text on the command line. Exit status of the system command is returned in variables GPVAL_SYSTEM_ERRNO and GPVAL_SYSTEM_ERRMSG.

CHANGE (differs from versions 4 through 5.2): Internal carriage-return ('r') and newline ('n') characters are not stripped from the input stream during substitution. This change brings backquote substitution in line with the system() function.

Command-line substitution can be used anywhere on the gnuplot command line except inside strings delimited by single quotes.

Example:

This will run the program leastsq and replace leastsq (including backquotes) on the command line with its output:

         f(x) = `leastsq`

or, in VMS

         f(x) = `run leastsq`

These will generate labels with the current time and userid:

         set label "generated on `date +%Y-%m-%d` by `whoami`" at 1,1
         set timestamp "generated on %Y-%m-%d by `whoami`"