Bash script to detect empty message string. Getting: too many arguments

Question

I have a bash script where I can pipe in output from another application into the below script. But I think I have an incorrect logic for testing if the message is empty or not. If its empty I want it to do nothing, but if it detects the word "error" in the string, it should run another function.

What am I doing wrong in my logic?

I'm getting too many arguments on the 3rd to the last line, most likely due to the message being empty.

message=$( cat )

if [ -n "${message// /}" ]; then
  #execute if the the variable is not empty and contains non space characters
  message="\`\`\` ${message} \`\`\`"
else
  #execute if the variable is empty or contains only spaces
  message=""
fi

sendX() {
.....
}

if  [ -z "$message" ]; then
        echo "Please pipe a message to me!"
else
        sendX
fi

sendAlert() {
......
}

checkword="error"

echo $message

if [ $message =~ $checkword ]; then  <---- Error: too many arguments
 sendY
fi

Answer 1

You're getting a "too many arguments" error since [ ... ] does not understand the =~ operator (used in bash for regular expression matching). Since [ ... ] does not understand the operator, it is treated as a string. You then have [ ... ] with three strings inside it, and they don't fulfil the semantic requirements for a proper test, which is why bash errors out at this point.

In bash, you would use =~ inside of [[ ... ]].

However, what I assume you'd like to do in that test is to see whether $message contains $checkword as a substring. This could also be done with

[[ "$message" == *"$checkword"* ]] && sendY

or with case ... esac:

case $message in
    *"$checkword"*) sendY
esac

This way you don't have to worry about $checkword containing characters that may be special in regular expressions.

You also need to double quote $message in echo $message, or you may get unexpected output if $message contains filename globbing characters like *.

Related:

• Bash - If Syntax confusion
• What is the difference between the Bash operators [[ vs [ vs ( vs ((?
• When is double-quoting necessary?
• Why is printf better than echo? (because it would be better to use printf '%s\n' "$message" than echo "$message" for user-supplied data)
• https://www.shellcheck.net/ (which would have picked up these issues and possibly others, like missing a proper #!-line)

---

You could also use this instead of the first operation in the script:

case $message in
    *[!\ ]*) # contains non-space
        message='``` '"$message"' ```' ;;
    *)       # contains nothing or only spaces
        message=
esac

Using case ... esac in both places would make your script (at least the bits that you have shown) portable to any sh-like shell.