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Laurence MorganAbout 1 min


Command line flag parser for Murex shell scripting


One of the nuisances of shell scripts is handling flags. More often than not your script will be littered with $1 still variables and not handle flags shifting in placement amongst a group of parameters. args aims to fix that by providing a common tool for parsing flags.

args takes a name of a variable to assign the result of the parsed parameters as well as a JSON structure containing the result. It also returns a non-zero exit number if there is an error when parsing.


args var-name { json-block } -> <stdout>


#!/usr/bin/env murex

# First we define what parameters to accept:
# Pass the `args` function a JSON string (because JSON objects share the same braces as murex block, you can enter JSON
# directly as unescaped values as parameters in murex).
# --str: str == string data type
# --num: num == numeric data type
# --bool: bool == flag used == true, missing == false
# -b: --bool == alias of --bool flag
args args %{
    AllowAdditional: true
    Flags: {
        --str:  str
        --num:  num
        --bool: bool
        -b: --bool
catch {
    # Lets check for errors in the command line parameters. If they exist then
    # print the error and then exit.
    err $args.error
    exit 1

out "The structure of \$args is: ${$args->pretty}\n\n"

# Some example usage:
# -------------------

!if { $(args.Flags.--bool) } {
    out "Flag `--bool` was not set."

# `<!null>` redirects the STDERR to a named pipe. In this instance it's the 'null' pipe so equivalent to 2>/dev/null
# thus we are just suppressing any error messages.
try <!null> {
    $(args.Flags.--str) -> set fStr
    $(args.Flags.--num) -> set fNum

    out "Defined Flags:"
    out "  --str == $(fStr)"
    out "  --num == $(fNum)"

catch {
    err "Missing `--str` and/or `--num` flags."

$args[Additional] -> foreach flag {
    out "Additional argument (ie not assigned to a flag): `$(flag)`."

See Also

This document was generated from builtins/core/management/shell_doc.yamlopen in new window.

Last update:
Contributors: Laurence Morgan,Laurence Morgan