How do I determine whether a variable contains a substring?
if [[ $foo = *bar* ]]
The above works in virtually all versions of Bash. Bash version 3 also allows regular expressions:
if [[ $foo =~ ab*c ]] # bash 3, matches abbbbcde, or ac, etc.
If you are programming in the BourneShell instead of Bash, there is a more portable (but less pretty) syntax:
case "$foo" in
*bar*) .... ;;
esaccase allows you to match variables against globbing-style patterns. If you need a portable way to match variables against regular expressions, use grep or egrep.
if echo "$foo" | grep bar >/dev/null; then ...