The following code
if [ $a == "apple" ]; then echo "True" else echo "False" fi outputs "True" ("False") if a="apple" (a="plum"). The comparison fails if one uses wildcards:
if [ $a == "appl"* ]; and is fixed if one replaces [ by [[:
if [[ $a == "appl"* ]]; What is the difference between [ and [[ in if statements?
[ is a command (basically a variant of the test command). [[ is a builtin in many shells.foo* inside [...] filename expansion (aka globbing) occurs; while inside [[...]] pattern matching occurs.[[ is more powerful and capable than [ but should not be used if portability is a concern.[ and [[ are not part of the if syntax, you can use them as in [ "$exit" = 'yes' ] && exit.[...] you should prefer = instead of ==. As far as I know, the second one is accepted in many shells but is not POSIX-compliant.By the way, I recommend you to double-quote your variables even if you really know how word splitting will behave.
