Case insensitive comparison of strings in shell script

All of these answers ignore the easiest and quickest way to do this (as long as you have Bash 4):

if [ "${var1,,}" = "${var2,,}" ]; then
  echo ":)"
fi

All you're doing there is converting both strings to lowercase and comparing the results.

In Bash, you can use parameter expansion to modify a string to all lower-/upper-case:

var1=TesT
var2=tEst

echo ${var1,,} ${var2,,}
echo ${var1^^} ${var2^^}