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Re: question about perl

by Trimbach (Curate)
on Mar 13, 2002 at 00:37 UTC( #151279=note: print w/replies, xml ) Need Help??

in reply to How do I change the shebang line for all perl scripts in a directory

If all your scripts are in one directory, and they all end with (for example) .pl, you can do it in one line from a UNIX shell:

user% perl -pi.bak -e 'BEGIN{undef $/};s[^#\!/usr/local/bin/perl][#\!/usr/bin/perl]' *.pl

One-liners rock!

Gary Blackburn
Trained Killer

Correction: Code enhanced thanks to mahi

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Re: Re: question about perl
by rnahi (Curate) on Mar 13, 2002 at 07:31 UTC
    It is true that your script will replace the Perl path within the shebang string, but it will also replace it if the same string is anywhere inside the script.
    perl -pi.bak -e 's[^#!/usr/local/bin/perl][#!/usr/bin/perl]' *.pl
    This one should guarantee that the replacement happens only at the beginning of a string. To ensure that the replacement is carried out only once in each script, though, one more check is needed.
    perl -pi.bak -e 'BEGIN{$c=@ARGV};s[^#!/usr/local/bin/perl][#!/usr/bin/ +perl] && $c-- if $c> @ARGV' *.pl
    which translates roughly into
    #!/usr/bin/perl -w -i.bak use strict our $count=@ARGV; while (<>) { if ($count > @ARGV) { s[^#!/usr/local/bin/perl][#!/usr/bin/perl]; $count--; } print; }
      Yeah, I know about the "anywhere in the script" thingy, but
      perl -pi.bak -e 's[^#!/usr/local/bin/perl][#!/usr/bin/perl]' *.pl
      yields a "/usr/local/bin/perl][: Event not found." error on my Perl 5.6.1 system, which is why I didn't post my original answer with an anchor metacharacter. Don't really know why the "^#!" is freaking out the regex, but on further examination it looks like the ! has to be escaped. I've corrected the code in my original post to compensate.

      And all of this:

      perl -pi.bak -e 'BEGIN{$c=@ARGV};s[^#!/usr/local/bin/perl][#!/usr/bin/ +perl] && $c-- if $c> @ARGV' *.pl
      can replaced with this:
      perl -pi.bak -e 'BEGIN{undef $/};s[^#\!/usr/local/bin/perl][#\!/usr/bi +n/perl]' *.pl
      ...which at least saves some typing, and is a bit more understandable besides. :-D

      Gary Blackburn
      Trained Killer

      Update: The exclamation mark needs escaping because I'm using tcsh, a csh-style shell. Anyone using a different type of shell (such as bash or other Bourne-type shell) shouldn't have to escape the ! at all. What a pain in the butt... :-(

        This is my output from Deparse in both Perl 5.6.0 and 5.6.1
        perl -MO=Deparse -pi.bak -e "s[^#!/usr/local/bin/perl][#!/usr/bin/perl +]" LINE: while (defined($_ = <ARGV>)) { s[^#!/usr/local/bin/perl][#!/usr/bin/perl]; } continue { print $_; } -e syntax OK
        There was no need for escaping the "!" and it worked fine (I searched perlre about the need for escaping the bang, but I couldn't find it. Did I miss something?).
        So I couldn't replicate your error condition. Sorry.
        However, I agree that your script is more readable. :)

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