Please can any one explain this ${0##/}

Shell Programming and Scripting
1

I did not understand what is ${0##/}

PGM=${0##/}
TMP=/tmp/${PGM}.$$

Please explain me.

2

'man ksh' yields the following:

       ${name#pattern}, ${name##pattern}
              If pattern matches the beginning of the value of parameter name,
              the  matched text is deleted from the result of substitution.  A
              single # results in the shortest match, two #'s results  in  the
              longest match.

       ${name%pattern}, ${name%%pattern}
              Like  ${..#..}  substitution, but it deletes from the end of the
              value.
3

PGM=${0##/}
TMP=/tmp/${PGM}.$$

$0 is the complete-name-of-the-script in side the script (e.g. /home/mydir/myscript.sh)

So, ${0##/} means the complete-name-of-the-script without the starting-slash (if it exists)!!

But, what I thing you wanted to write is:

PGM=${0##*/}

which means complete-name-of-the-script without everthing up to and including the last-slash (e.g. myscript.sh)

Then, $$ is the Process-ID of the current script. So, TMP will be set to be /tmp/myscript.sh.1234 (where 1234 is the process-id).

This combination is normally used to create unique (i.e. different for each running script) names.