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Fix the Shell function Warning: POSIX sh vs Bash

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In a #!/bin/sh script, declare a function as hello() { ...; }, without the function keyword. If the script needs Bash syntax, select Bash and invoke it accordingly. Calling sh script.sh does not follow a Bash shebang in that file.

ShellCheck SC2112 explains that function is not POSIX sh syntax. A particular /bin/sh implementation accepting it does not establish portability.

Write a function for the selected shell

Save this as greet.sh. Quoting "$1" and "$@" preserves spaces and wildcard characters in arguments.

greet.sh

#!/bin/sh
set -eu

greet() {
    if [ "$#" -ne 1 ]; then
        printf '%s\n' 'usage: greet.sh NAME' >&2
        return 2
    fi
    printf 'Hello, %s\n' "$1"
}

greet "$@"
sh -n greet.sh
sh greet.sh 'Ada Lovelace'
sh greet.sh 'Ada *'

The outputs are Hello, Ada Lovelace and Hello, Ada *. sh -n checks syntax only, so also execute the script. Missing or extra arguments produce usage text on stderr and exit status 2. A valid argument produces status 0.

Distinguish the shebang from an explicit interpreter

Invocation Interpreter selection
sh greet.sh NAME The invoked sh reads the file.
bash greet.sh NAME Bash reads it.
chmod +x greet.sh, then ./greet.sh NAME This execution uses the file’s shebang.

For Bash arrays or [[ ... ]], use #!/usr/bin/env bash and run bash script.sh or the executable ./script.sh. Do not expect Bash syntax when invoking sh script.sh. ShellCheck’s shell-selection explanation.

A function’s return passes control and a status back to its caller. exit terminates the running shell. Here the function is the final command, so its status becomes the script’s exit status.

The example was checked with spaced and wildcard arguments and invalid argument counts. /bin/sh implementations differ, so test on the deployment shell too. For the next automation step, see numeric version comparison or GitHub release lookup, where inputs and failure statuses also matter.

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