Cant get "=~" to work. Keep getting "[: =~: binary operator expected" [closed]

Question

When I try and use if [ "$1" =~ "$regex" ]; then

I keep on getting back the same error: [: =~: binary operator expected

Here is an example function where I get the error:

char_check() {
  regex='^[]0-9a-zA-Z,!^`@{}=().;/~_|[-]*$'
  if [ "$1" =~ "$regex" ]; then
    echo "No illegal characters."
  else
    echo "Illegal characters."
  fi
}

Any response would be a great help.

Answer 1

Regular expressions require [[ expression ]] as shown in the man page of bash.

Also you must not quote the regex itself, e.g. you should prefer $regex over "$regex"

char_check() {
  regex='^[]0-9a-zA-Z,!^`@{}=().;/~_|[-]*$'
  if [[ "$1" =~ $regex ]]; then
    echo "No illegal characters."
  else
    echo "Illegal characters."
  fi
}

If you quote the regex then you are trying to match the string, not the pattern. In other words it will match the weird string '^[]0-9a-zA-Z,!^`@{}=().;/~_|[-]*$'