Bash

Length

Depending on var type you can have the length of the variable :

$ TEST=toto
$ echo ${TEST}
toto
$ echo ${#TEST}
4
$ ARR=(toto tata titi)
$ echo ${#ARR}
3

Default

If you want to put default value to your variable you can as well :

$ echo ${TEST:-toto}
toto
$ echo ${TEST}

$ TEST=titi
$ echo ${TEST:-toto}
titi

You can also assign default :

$ echo ${TEST:=toto}
toto
$ echo ${TEST}
toto

You can also test if assigned

$ echo ${TEST:?"No value there"}
-bash: TEST: No value there
$ TEST=toto
$ echo ${TEST:?"No value there"}
toto

Transformations

Removal

You can remove pattern in varaible using # (from left) or % (from right)

$ TEST="tototatatititatatoto"
$ echo ${TEST#*tata}
tititatatoto
$ echo ${TEST%tata*}
tototatatiti

This will remove the shortest pattern
You can also remove the longest pattern with this :

$ TEST="tototatatititatatoto"
$ echo ${TEST##*tata}
toto
$ echo ${TEST%%titi*}
tototata

You can do the same on array and it will apply to each member :

$ TEST=(toto tata titi tata toto)
$ echo ${TEST[@]#toto}
tata titi tata
$ echo ${TEST[@]#*a}
toto ta titi ta toto
$ echo ${TEST[@]##*a}
toto titi toto

Change of case

You can do some upper or lower case change directly on the variable:

$ TEST="TOTO"
$ echo "${TEST,}"
$ tOTO
$ echo "${TEST,,}"
$ toto

And the opposite :

$ TEST="toto"
$ echo "${TEST^}"
$ Toto
$ echo "${TEST^^}"
$ TOTO

Substitution

Same as using sed pretty much :

$ TEST="tototatatititatatoto"
$ echo ${TEST/o/a}
tatotatatititatatoto
$ echo ${TEST//o/a}
tatatatatititatatata