How to test for a character (or string) in a filename in dash

Question

I have a string (a filename, actually) that I want to test whether they contain a character:

NEEDLE="-"
for file in mydirectory/*
do
   if [NEEDLE IS FOUND IN STRING]
   then
       # do something
   else
       # do something else
   fi
done

Basically this is the same question as String contains in Bash, except for dash instead of bash (ideally shell-neutral, which is usually the case with dash-code anyway)

The [[ operator does not exist in dash, therefore the answer to that question does not work.

Answer 1

use a case statement, no need to spawn an external program:

NEEDLE="-"
for file in mydirectory/*; do
    case "$file" in
        *"$NEEDLE"*) echo "do something" ;;
        *) echo "do something else" ;;
    esac
done

Answer 2

You can just use grep -q inside for loop:

NEEDLE="-"
for file in mydirectory/*; do
    if grep -q "$NEEDLE" "$file"; then
       echo "do something"
    else
       echo "do something else"
    fi
done