How do I determine whether a variable contains a substring?
# Bash if [[ $foo = *bar* ]]
The above works in virtually all versions of Bash. Bash version 3 (and up) also allows regular expressions:
# Bash my_re='ab*c' if [[ $foo =~ $my_re ]] # bash 3, matches abbbbcde, or ac, etc.
For more hints on string manipulations in Bash, see FAQ #100.
If you are programming in the POSIX sh syntax or for the BourneShell instead of Bash, there is a more portable (but less pretty) syntax:
# Bourne case $foo in *bar*) .... ;; esac
case allows you to match variables against globbing-style patterns (including extended globs, if your shell offers them). If you need a portable way to match variables against regular expressions, use expr.
# Bourne/POSIX if expr "x$foo" : 'x.*bar' >/dev/null; then ...