How do I change the case (upper and lower case) of strings in my variable?

Question

"Enter test: "
read test

if [[ $test == "a" ]]; then
    echo "worked"
else
    echo "failed"
fi

It's a simple illustration of test I'm doing, but if I enter "A", it will fail. Is there anything I can do at the variable stage to change it all to small case, so that the test will match?

Answer 1

Just use the standard sh (POSIX and Bourne) syntax:

case $answer in
  a|A) echo OK;;
  *)   echo >&2 KO;;
esac

Or:

case $answer in
  [aA]) echo OK;;
  *)    echo >&2 KO;;
esac

With bash, ksh or zsh (the 3 shells that support that non-standard [[...]] syntax), you can declare a lower case variable:

typeset -l test
printf 'Enter test: '
read test
if [ "$test" = a ]; then...

(beware that bash's case conversion is bogus in some locales).

Answer 2

There are several useful ways to achieve this (in bash):

two checks

echo -n "Enter test: "
read test

if [[ $test == "a" || $test == "A" ]]; then
    echo "worked"
else
    echo "failed"
fi

make the input lower case

echo -n "Enter test: "
read test
test="${test,,}"

if [[ $test == "a" ]]; then
    echo "worked"
else
    echo "failed"
fi

regex for both cases

echo -n "Enter test: "
read test

if [[ $test =~ ^[aA]$ ]]; then
    echo "worked"
else
    echo "failed"
fi

make the shell ignore the case

echo -n "Enter test: "
read test

shopt -s nocasematch
if [[ $test == a ]]; then
    echo "worked"
else
    echo "failed"
fi

Answer 3

There are several ways to do this. If you're using a recent version of bash it's quite easy: you can convert the case of test, or you can use a regex to match both upper & lower case a.

First the regex way:

read -p "enter test: " test;[[ $test =~ ^[Aa]$ ]] && echo yes || echo no

Now the case shifter:

read -p "enter test: " test;[[ ${test^^} = A ]] && echo yes || echo no

Answer 4

sed -ne '/^[aA]$/!i\' -e failed -e 's//worked/p;q' </dev/tty