How do I determine whether a variable contains a substring?

In BASH:

  # 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 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 grep or egrep.

  # Bourne
  if echo "$foo" | grep bar >/dev/null 2>&1; then ...

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