regex - 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