this="${0##*/}"

[zb cong]

hello

i read a kshell script, find a line as---this="${0##*/}"

in the beginning part of the script, i have check the document, and can't figure out what on earth it mean,please help me.


thank you

[Joe Ess]

Have you tried typing it into a shell and seeing what it does? Remember, a shell script is just a series of commands. When I do it in a Cygwin Bash shell, I get the name of the shell:

[Administrator@JoesLaptop] ~
$ export this=${0##*/}
 
[Administrator@JoesLaptop] ~
$ echo ${this}
bash

Another clue is how the variable is used from then on? Is it compared to values? Used in calculations?

[zb cong]

yes, you are right, in the script, it used to get the script name. but what i feel stranged is the content---0##*/, what is it? it is not a unix command and i can't find it from kshell document, so it is not the syntax of kshell, originally, it seem like the regular expression. but it is not.

WHAT ON EARTH IS IT?

thanks

[Joe Ess]

It's the shell syntax for parameter substitution.

[Tim Holloway]

Wow. If I typed words like that, I'd get my mouth washed out with soap.

Seriously, it's an interesting little critter that runs a regular expression on a shell parameter. Here's a snipper from the ksh man page:

       ${parameter#pattern}
       ${parameter##pattern}
              If the shell pattern matches the beginning of the value of parameter, then the value
              of this expansion is the value of the parameter with the  matched  portion  deleted;
              otherwise  the value of this parameter is substituted.  In the first form the small-
              est matching pattern is deleted and in the second form the largest matching  pattern
              is deleted.  When parameter is @, *, or an array variable with subscript @ or *, the
              substring operation is applied to each element in turn.