How to replace a string in an existing file in Perl

Use a one-liner:

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

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