jbullock35 has asked for the wisdom of the Perl Monks concerning the following question:

$` can often be replaced by (.*?) at the head of a regular expression. But how can
$` be replaced if one wants to do a global substitution with /g? For example, how
can 
s<(\w+)/><$`$1\n>g

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be replaced by some variation that uses (.*?) or something close to it?

(To clarify, the substitution above replaces each match with a substring extending
from the beginning of the string through the last character of the match. So
Call/me/Ishmael/
becomes
Call
Call/me
Call/me/Ishmael
after the substitution.)

Thanks,
––John

Replies are listed 'Best First'.
Re: replacing $` with ordinary capturing in global substitutions
by borisz (Canon) on Sep 01, 2004 at 10:15 UTC 
    s<(\w+)/><substr( $_, 0, pos $_). "$1\n">ge;

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    Boris
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[d/l]

      I guess you never tested this. pos() doesn't work inside of a s///: 

      #!/usr/bin/perl -w
use strict;

$_= "This/is/a/test";
s<(\w+)/><$`$1\n>g;
print $_,$/,$/;

$_= "This/is/a/test";
s<(\w+)/><substr( $_, 0, pos $_). "$1\n">ge;
print $_,$/;

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      produces: 

      This
This/is
This/is/a
test

Use of uninitialized value in substr at - line 9.
Use of uninitialized value in substr at - line 9.
Use of uninitialized value in substr at - line 9.
This
is
a
test

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      - tye        

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[d/l]
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        Tested and it works fine for me. 
        __OUTPUT__
This
This/is
This/is/a
test

This
This/is
This/is/a
test

~ borisz$ perl -V
Summary of my perl5 (revision 5 version 8 subversion 4) configuration:
  Platform:
    osname=darwin, osvers=7.3.0, archname=darwin-thread-multi-2level

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        What perl version do you use?
        Boris
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Re: replacing $` with ordinary capturing in global substitutions
by PodMaster (Abbot) on Sep 01, 2004 at 10:29 UTC
    one 
    my @string = grep length, split '\/', 'Call/me/Ishmael/';
for my $i( 0 .. $#string ){
    print join('/', @string[0..$i]),"\n";
}
__END__
Call
Call/me
Call/me/Ishmael

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    two 
    local $fungus = '';
local $_ = 'Call/me/Ishmael/';
s'
 (\W*)?
 (\w+)?
 '
   $fungus .= $1 if $1;
   $fungus .= $2 if $2;
   $2 ? "$fungus\n" : "";
 'gex;
print 
__END__
Call
Call/me
Call/me/Ishmael

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    update: nice one borisz++ (i thought about using pos for three, but figured nah)

    MJD says "you can't just make shit up and expect the computer to know what you mean, retardo!"
    I run a Win32 PPM repository for perl 5.6.x and 5.8.x -- I take requests (README).
    ** The third rule of perl club is a statement of fact: pod is sexy.

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Re: replacing $` with ordinary capturing in global substitutions
by Roy Johnson (Monsignor) on Sep 01, 2004 at 15:02 UTC 
    my $old;
s<\G(.*?\w+)><$old.=$1;"$old\n">ge;

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    Caution: Contents may have been coded under pressure.
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[d/l]
Re: replacing $` with ordinary capturing in global substitutions
by Anonymous Monk on Sep 02, 2004 at 09:30 UTC 
    s<(\w+)/><@{[substr $_, 0, $-[0]]}$1\n>g;

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[d/l]

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