Regex to find/replace in a file

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

I am very new to programming, and I suspect the answer to this will be laughably obvious, but here goes: I want to use regular expressions to find and replace all occurrences of a string in an entire file. In the Q&A section I found a snippet to find a string in a file:

{
    open(FILE, "sample.txt") or die "Can't open sample.txt\n";
    local $/ = undef;
    $lines = <FILE>;
    close(FILE);
}
if($lines =~ /foo/) {
print "A match was found\n"
}
[download]

All very well and good. But how do I replace "foo" with "bar"? I tried this:

$lines =~ s/foo/bar/gms;
[download]

but it doesn't do anything to the other file. Help! Thank you!

Comment on Regex to find/replace in a file Select or Download Code

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Re: Regex to find/replace in a file by VSarkiss (Monsignor) on May 16, 2002 at 19:08 UTC
You're on the right track. After this: `$lines =~ s/foo/bar/gms;`the substitution has been made, but it's still in memory. The next step is to write it to the file: `open(FILE, ">theother.txt") or die "Can't open the other file: $!\n"; print FILE $lines; close FILE;` [download] You said "other file", so I'm not sure if you want to overwrite the original file or not. If you do, just substitute its name instead of `theother.txt` above. HTH	[reply] [d/l] [select]
Re: Re: Regex to find/replace in a file by amarceluk (Beadle) on May 16, 2002 at 19:14 UTC
Thank you! It worked, and I'm extremely happy about it :-)	[reply]
Re: Regex to find/replace in a file by yodabjorn (Monk) on May 16, 2002 at 21:01 UTC
This can also be done on the cmd line verry easily: `perl -i.bak -lpe 's/foo/bar/g;' baz` [download] This would replace all occurances of foo with bar in file baz backing up the original (unalterd file) to baz.bak	[reply] [d/l]