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

I'm attempting to search through a file for a certain piece of text, and if it exists, replace it with something else. That part works fine, but here's the catch: if the text isn't in the file, I want to have the script add in some new text at the end of the file. Is there a way to find out if a search and replace like $var =~ s/something/somethingelse/; replaced anything or not?

Replies are listed 'Best First'.
Re: Conditional replace
by busunsl (Vicar) on Aug 23, 2001 at 12:07 UTC
    The s/// operator returns the number of substitutions.
    So something like: do_something() if s/foo/bar/; should do the trick.
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[d/l]
Re: Conditional replace
by clemburg (Curate) on Aug 23, 2001 at 12:10 UTC

    Like this:

    try.pl: 

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

my $count = 0;

while (<>) {
    $count += s/foo/bar/g;
    print;
}

print "Nothing found!\n" unless $count;

    [download]

    Show it in action: 

    H:\>cat try1.txt
bla
blurb
foo foo
foo
lilalu

H:\>cat try2.txt
bla
blurb
fuu fuu
fuu
lilalu

H:\>cat try1.txt | perl try.pl
bla
blurb
bar bar
bar
lilalu

H:\>cat try2.txt | perl try.pl
bla
blurb
fuu fuu
fuu
lilalu
Nothing found!

H:\>

    [download]

    Christian Lemburg
    Brainbench MVP for Perl
    http://www.brainbench.com

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[d/l]
[select]
Re: Conditional replace
by lestrrat (Deacon) on Aug 23, 2001 at 12:07 UTC

    Something like this?

    my $add_at_end = 1;
while( my $ln = <IN> ) {
       if( $ln =~ s/str1/str2/ && $add_at_end ) {
              $add_at_end = 0;
       }
       print OUT $ln;
}

print OUT "text" $add_at_end;

    [download]
[reply]
[d/l]
      Your last print has a typo :-) your logic is backwards :-) and its simpler IMO to say:
      my $add_at_end;
while (<IN>) {
 $add_at_end = 1 unless s/str1/str2/;
 print OUT;
}
print OUT "text" if $add_at_end;

      [download]
      Update:And I had a typo also. Fixed mine first :-)
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[d/l]
Re: Conditional replace
by George_Sherston (Vicar) on Aug 23, 2001 at 12:58 UTC
    Another way:$FileText =~ s/($Search|$)/$1 eq $Search ? $Replace : $AddText/e;

    § George Sherston
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[d/l]
Re: Conditional replace
by October (Initiate) on Aug 24, 2001 at 04:02 UTC
    thanks. works now :)
[reply]

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