How to replace a string in an existing file in Perl?

Question

I want to replace word \"blue\" to \"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 this code

Answer 1

It can be done using a single line:

perl -pi.back -e 's/oldString/newString/g;' inputFileName

Pay attention that oldString is processed as a Regular Expression.
In case the string contains any of {}[]()^$.|*+? (The special characters for Regular Expression syntax) make sure to escape them unless you want it to be processed as a regular expression.
Escaping it is done by \, so \[.