Case insensitive comparison of strings in shell script

Question

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^^}

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.

if you have bash

str1="MATCH"
str2="match"
shopt -s nocasematch
case "$str1" in
 $str2 ) echo "match";;
 *) echo "no match";;
esac

otherwise, you should tell us what shell you are using.

alternative, using awk

str1="MATCH"
str2="match"
awk -vs1="$str1" -vs2="$str2" 'BEGIN {
  if ( tolower(s1) == tolower(s2) ){
    print "match"
  }
}'

Save the state of nocasematch (in case some other function is depending on it being disabled):

local orig_nocasematch=$(shopt -p nocasematch; true)
shopt -s nocasematch

[[ "foo" == "Foo" ]] && echo "match" || echo "notmatch"

$orig_nocasematch

Note that local is only required inside a function.
Also, the ; true part will prevent the shell from exiting when set -e is on and $(shopt -p nocasematch) fails (because nocasematch was NOT set at all).

One way would be to convert both strings to upper or lower:

test $(echo "string" | /bin/tr '[:upper:]' '[:lower:]') = $(echo "String" | /bin/tr '[:upper:]' '[:lower:]') && echo same || echo different

Another way would be to use grep:

echo "string" | grep -qi '^String$' && echo same || echo different

For korn shell, I use typeset built-in command (-l for lower-case and -u for upper-case).

var=True
typeset -l var
if [[ $var == "true" ]]; then
    print "match"
fi

Very easy if you fgrep to do a case-insensitive line compare:

str1="MATCH"
str2="match"

if [[ $(fgrep -ix $str1 <<< $str2) ]]; then
    echo "case-insensitive match";
fi