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

So, under 5.005_03 this works fine: 
sub changeme{  
  local $^I = ".$bak";
  @ARGV = "somefile";
  while (<>) {
    s/foo/bar/i;
    print;
  }
}

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However, substitute a variable in for bar: 
sub changeme{
  $myvar = somesub();
  local $^I = ".$bak";
  @ARGV = "somefile";
  while (<>) {
    s/foo/$myvar/i;
    print;
  }
}

[download]
And nothing happens - it just hangs. Why?

Replies are listed 'Best First'.
Re: Edit in place (part2)
by GrandFather (Saint) on May 01, 2006 at 20:43 UTC

    Seems most likely there is something external going on, like the file is accessed over a slow network or is mapping to the console in some fashion. On the face of it the code is fine.

    DWIM is Perl's answer to Gödel
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Re: Edit in place (part2)
by ikegami (Patriarch) on May 01, 2006 at 20:40 UTC

    Dunno, but you could try replacing
    s/foo/$myvar/i;
    with
    substr($_, $-[0], $+[0] - $-[0], $myvar) if /foo/i;

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[d/l]
[select]
Re: Edit in place (part2)
by CountOrlok (Friar) on May 01, 2006 at 20:40 UTC
    $myvar may have meta characters. See the quotemeta function, i.e. $myvar = quotemeta(somesub());
    -imran
[reply]
[d/l]
      No, $myvar can safely contain any character. You only need to escape text interpolated into the regexp, not the replace string.
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[d/l]
Re: Edit in place (part2)
by davidrw (Prior) on May 01, 2006 at 20:39 UTC
    doesn't answer the "why" (may extra data point??), but does s/foo/$myvar/ie; work?
[reply]
[d/l]
      No, however it's hanging before the regex. In a truss you see the somesub() and then it sleeps. I'm just grasping at straws, but I feel that it's about the ARGV. The <> is getting mucked somehow.
[reply]
        Can you post the code that is in somesub()?
        -imran
[reply]

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