Regular expressions are a means of matching a pattern of characters within a string.
Regular expressions (regex or regexp for short) are patterns that describe a set of strings based on simple syntactic criteria.
Tools such as grep, sed and awk involve regular expression matching as a key feature. Most programming languages include a regular expression library, and most text editors provide regular expression search and replacement.
Shell wildcards for file names (also called glob patterns) are a different, less powerful syntax (though ksh, bash and zsh have more powerful extensions). Bash, ksh93 and zsh's
=~ operator offer regex matching.