functions.sh

# For reference: 1>&2 redirects output to stderr


# This script should only be sourced by other scripts
if [[ "$0" != '-bash' ]] ; then
    echo 'WARNING: functions.sh should be sourced, not executed' 1>&2
fi

# Check for an error, and optionally display a message
function check_ok() {
    local errcode=$?
    if [[ "$errcode" -ne 0 ]] ; then
        if [ -n "$1" ] ; then
            echo "$1" 1>&2
        fi
        return $errcode
    else
        return 0
    fi
}

# Check that a file exists, and optionally display a message
function check_exists() {
    if [ -z "$1" ] ; then
        echo 'Usage: check_exists <filepath> [<error message>]' 1>&2
        return 1
    fi
    local filename=$1
    if [[ ! -f "$filename" ]] ; then
        if [ -n "$2" ] ; then
            echo "$2" 1>&2
        fi
        return 1
    else
        return 0
    fi
}

function _test_check_ok_inner() {
    ls /invalid/path/bogus-filename.ext 2> /dev/null
    check_ok "check_ok test passed" || return $?
    echo "check_ok test failed" 1>&2
}

function _test_check_exists() {
    check_exists /invalid/path/bogus-filename.ext "check_exists test passed"
    check_ok "check_exists returned correct error code" || return $?
    echo "check_exists returned wrong error code" 1>&2
}

function _test_check_exists_bad_invocation() {
    # This fails because 
    export err_code=0
    local err_msg=$(check_exists 2>&1 ; err_code=$?)
    echo "err_code=$err_code"
    echo "err_msg=$err_msg"
    echo "\$?=$? when capturing output"
    check_ok "check_exists returned correct error code" || return $?
    echo "check_exists returned wrong error code" 1>&2
}

function test_functions() {
    _test_check_ok_inner
    _test_check_exists
    _test_check_exists_bad_invocation
}

Work in progress