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Re: capturing sub-expressions?


From: Linda Walsh
Subject: Re: capturing sub-expressions?
Date: Tue, 29 Jan 2008 17:41:35 -0800
User-agent: Thunderbird 2.0.0.9 (Windows/20071031)

Paul Jarc wrote:
Linda Walsh <address@hidden> wrote:
In my copy of the man pages, Pattern matching is indented an extra
level making it look like it's under Pathname Expansion and only
applies there....

Pattern matching applies primarily to pathname expansion; other uses
explicitly refer to its use there:
       ${parameter/pattern/string}
              The pattern is expanded to produce a pattern just as in
              pathname expansion.  Parameter is expanded and the
              longest match of pattern against its value is replaced
              with string.  [...]

I wanted to leave "myswitch2" as the only thing left in $p;

p=" $p "
p=${p/* myswitch2 */myswitch}
p=${p/ */}
-----
        I simplified my example a bit too much...

p="-e -p 60 -x"
---
That's why I wanted the capture -- to pick out the 60 -- where 60 represents
a positive integer.  The space between the -p and the number is optional.

I can get at the 60 using multiple "nibbles" off the front and end of
the string, but no [easy] way I can think of to get at it directly.
I figured with "capture", I could substitute it in as the replacement
string.  with nibbling, it makes for convoluted code that doesn't
feel "robust" (and I can easily come up with specific (though unlikely
to be used in practice) examples to cause failure).

Harder targets included more "switches" (-b, -v and -t which all take
arguments which may or may not be separated from the switch by a space.
Switches (and their values) are space separated.  I'm not worrying
about supporting embedded spaces in filenames.

p="-e -p60 -b 1m -v string -tfile"

Switch -b has some decimal value with an optional suffix in the set
"kmgtpesb".  But the above target isn't really needed AFAIK in the near
future.




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