Ignore case from user input

Question

I'm trying to write a script to catch user input. The script should ignore the case.

Consider this script foo.sh:

if [ $1 == "string" ]; then
  echo true
else
  echo false
fi

If the input of foo.shis STRING or StRiNg the result is going to be false.

How can I ignore the case in the if condition?

Solution 1

Assuming you are using bash 4.0+:

${1,,}

Otherwise, tr or awk should work:

var=$(echo "$1" | awk '{print tolower($0)}')
var=$(echo "$1" | tr '[:upper:]' '[:lower:]')

Summaries:

• Awk takes in the input and simply prints $0 (the whole input line) after using the built in tolower() function.

• Tr looks pretty self explanatory, but let me know if you have questions on it.

Solution 2

declare has a lower-case function:

declare -l str=$1
[[ $str = "string" ]] && echo true || echo false

Comments

[mpy]

You should use [[ "$1" == "string" ]] instead of [ $1 == "string" ]. Otherwise you will get into trouble, if $1 contains spaces or is empty.

[glenn jackman]

better to quote "$a"

[gniourf_gniourf]

There's also the nocasematch shell option that could be used.