How to replace a string in an existing file in Perl

Question

I want to replace the word "blue" with "red" in all text files named as 1_classification.dat, 2_classification.dat and so on. I want to edit the same file so I tried the following code, but it does not work. Where am I going wrong?

@files = glob("*_classification.dat"); foreach my $file (@files) {     open(IN,$file) or die $!;     <IN>;     while(<IN>)     {         $_ = '~s/blue/red/g';         print IN $file;     }     close(IN) } 

Answer 1

Use a one-liner:

$ perl -pi.bak -e 's/blue/red/g' *_classification.dat 

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Explanation

• -p processes, then prints <> line by line
• -i activates in-place editing. Files are backed up using the .bak extension
• The regex substitution acts on the implicit variable, which are the contents of the file, line-by-line

Answer 2

None of the existing answers here have provided a complete example of how to do this from within a script (not a one-liner). Here is what I did:

rename($file, $file . '.bak'); open(IN, '<' . $file . '.bak') or die $!; open(OUT, '>' . $file) or die $!; while(<IN>) {     $_ =~ s/blue/red/g;     print OUT $_; } close(IN); close(OUT);