### Comparing the "job name"

The token `\jobname` amusingly produces a sequence of characters whose category code is 12 ('other'), regardless of what the characters actually are. Since one inevitably has to compare a macro with the contents of another macro (using `\ifx`, somewhere) one needs to create a macro whose expansion looks the same as the expansion of `\jobname`. We find we can do this with `\meaning`, if we strip the "`\show` command" prefix.

The full command looks like:

    \def\jobis#1{FF\fi
      \def\predicate{#1}%
      \edef\predicate{\expandafter\StripPrefix\meaning\predicate}%
      \edef\job{\jobname}%
      \ifx\job\predicate
    }

And it's used as:

    \if\jobis{mainfile}%
      \message{YES}%
    \else
      \message{NO}%
    \fi

Note that the command `\StripPrefix` need not be defined if you're using LaTeX - there's already an internal command `\strip@prefix` that you can use.