Path: utzoo!attcan!uunet!mcsun!ukc!axion!tharr!gustav
From: gustav@tharr.UUCP (Paul Moore)
Newsgroups: comp.lang.perl
Subject: Re: Need help with (\d+) problem (s/...(\d+)/$1/ not working?)
Message-ID: <1390@tharr.UUCP>
Date: 5 Nov 90 22:50:31 GMT
References: <1990Nov4.224658.21882@uvaarpa.Virginia.EDU>
Reply-To: gustav@tharr.UUCP (Paul Moore)
Organization: Power Microsystems Ltd
Lines: 42

In article <1990Nov4.224658.21882@uvaarpa.Virginia.EDU> telxon!ping!gorpong@uunet.uu.net writes:
>Something is a little strange either with the way that I am interpreting the
>manual page, or with Perl.  The mini-script:
>
>	$string = "this is a test of stuff\t95";
>	($a = $string) =~ s/\w+\s+(\d+)/$1/;
>	print "1 == $1\nA == $a\n+ == $+\nbefore == $`\nafter == $'\n";
>
>Prints out:
>
>	1 == 95
>	A == this is a test of 95
>	+ == 95
>	before == this is a test of 
>	after == 

This is correct.

The substitution is editing $a, not replacing it. The expression on the
second line works like this. First, you assign $string to $a, setting $a
to "this is a test of stuff\t95". This assignment returns an LVALUE, $a.
The =~ operator then applies the following substitution to this value.

s/\w+\s+(\d+)/$1/ looks through the string for a word (\w+) followed by
whitespace (\s+) followed by a number (\d+), finding "stuff\t95" in this
case. It then replaces this part of the string with the number ($1), but
*leaving the rest of the string as it was*. So, the result is "this is a
test of 95", as shown.

If you really do want $a to equal "95", you could just say $a = $1 at
the end ($1 keeps its value outside the replacement pattern). I'm sure
there are better ways, as well. (but I'm too tired to think of one just
now...)

Hope this helps,
Gustav.
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