One of many many ways, from the command line perl -pi -e's/\b(\d\d):(\d\d):\d\d\b/$1$2/g;' filename.ext \b is a word boundary, which helps narrow the selection. \d are digits, and we capture the significant ones with parens. That makes them available as $1, $2 in the substitution string. The /g modifier makes the substitution for all instances on a line.