Check if a variable exists in a list in Bash

Question

I am trying to write a script in bash that check the validity of a user input.
I want to match the input (say variable x) to a list of valid values.

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Answer 1

If the list is fixed in the script, I like the following the best:

validate() {
    grep -F -q -x "$1" <

Then use validate "$x" to test if $x is allowed.

If you want a one-liner, and don't care about whitespace in item names, you can use this (notice -w instead of -x):

validate() { echo "11 22 33" | grep -F -q -w "$1"; }

Notes:

• This is POSIX sh compliant.
• validate does not accept substrings (remove the -x option to grep if you want that).
• validate interprets its argument as a fixed string, not a regular expression (remove the -F option to grep if you want that).

Sample code to exercise the function:

for x in "item 1" "item2" "item 3" "3" "*"; do
    echo -n "'$x' is "
    validate "$x" && echo "valid" || echo "invalid"
done