[Leaplist] teach me please about this code

[John Simpson]

On 2008-01-03, at 1951, tonyb wrote:
>
> The easy way to understand it is by using echo to display the
> interesting pieces:
> ...
>
> for i in *.m4a
> do
>  echo "$i"
>  echo "${i%m4a}mp3"
> done
>
> aa.m4a
> aa.mp3
> bb.m4a
> bb.mp3
> cc.m4a
> cc.mp3

is the ${...%pattern} operator specific to bash, or does it work with  
any /bin/sh variant?

reading the man page about it, i also find a ${.../pattern/string}  
operator. i remember reading about these before, but i couldn't get my  
head wrapped around what they were doing, and it wasn't relevant to  
what i was working on at the time, so i ignored it but always meant to  
get back to it... and of course, never did.

i just wrote a test script to show me what these operators actually  
do. i find it easier to understand if i can see a list of "before and  
after" cases...

$x              abc_123_abc_789_abc
${x%abc}XYZ     abc_123_abc_789_XYZ
${x#abc}XYZ     _123_abc_789_abcXYZ
${x/abc/XYZ}    XYZ_123_abc_789_abc
${x//abc/XYZ}   XYZ_123_XYZ_789_XYZ
${x/#abc/XYZ}   XYZ_123_abc_789_abc

----------------------------------------------------------------
| John M. Simpson    ---   KG4ZOW   ---    Programmer At Large |
| http://www.jms1.net/                         <jms1 at jms1.net> |
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| http://video.google.com/videoplay?docid=-1656880303867390173 |
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