Bash - Best way to have helpFunction & default parameter values - bash

Question

After a lot of read, SO or others, I'm really wondering about the best / cleanest way to have a bash script with parameters, optionals with default values.
Here is my script for now:
#!/bin/bash
helpFunction()
{
echo ""
echo "Usage: $0 --reload --mode=[single|cluster]"
echo -e "\t--reload Reload the database : fixtures & schema"
echo -e "\t--mode Mode of build : single or cluster"
exit 1
}
while [[ "$#" -gt 0 ]]; do
case $1 in
-h|--help) helpFunction; shift ;;
-r|--reload) reload=true; shift ;;
-m|--mode) mode="single"; shift ;;
# ... (same format for other required arguments)
*) echo "Unknown parameter passed: $1" ;;
esac
shift
done
./bin/sh/tools/build.sh -e local -m $mode -p local
For now, the $mode variable seems to not be set if I don't set it, how can I have a default value for this variable ? (default is single)
What I want is the user to call the script like (reload is true, mode is cluster):
bin/script.sh -r --mode=cluster
Or by default (reload is false, mode is single):
bin/script.sh
Is this the good way to wait for parameters ? I read other ways, but no real explanations.
Thanks.

Answer 1

There is no universal best/cleanest method; it eventually comes down to what works best for you; some ideas:
set mode to a default value before the while/case loop
after the while/case loop test mode and if unset/undefined then set to a
default value (should probably play it safe and unset mode before the while/case loop though in this case you might as well see idea #1)
pass to build.sh wrapped in double quotes (ie, build.sh -e local -m "$mode" -p local) and have build.sh test for the -m argument being unset/undefined and set to a default value
a variation on #2 and #3 is to use parameter substitution when
passing mode to build.sh, eg: build.sh -e local -m "${mode:-default_value}" -p local
if your script sources a config/ini file you could assign mode a
default value in said config/ini file and then make sure said config/ini file is sourced before the while/case loop

Answer 2

If you set the mode beforehand, that will be its default. If you want parameter with assignment, you need to grab $2 and shift twice.
mode="single"
while [[ "$#" -gt 0 ]]; do
case $1 in
-h|--help) helpFunction; shift ;;
-r|--reload) reload=true; shift ;;
-m|--mode) mode="$2"; shift; shift ;;
# ... (same format for other required arguments)
*) echo "Unknown parameter passed: $1" ;;
esac
shift
done
I think it's also good to restore the positional arguments. Since you may want to use them, but that depends on your script.
mode="single"
reload="false"
POSITIONAL=()
while [[ "$#" -gt 0 ]]; do
case $1 in
-h | --help)
helpFunction
shift
;;
-r | --reload)
reload=true
shift
;;
-m | --mode)
mode="$2"
shift
shift
;;
*)
POSITIONAL+=("$1")
shift
;;
esac
done
set -- "${POSITIONAL[#]}"
COMMAND="$1"
Then you could invoke a function that is called like the $COMMAND and pass the rest of the params with $#, and shift again and set the subcommand to $1. You can do this infinitely to get a chain of (sub)commands.
You can still check if a valid command was provided before you try to call the $COMMAND.
COMMAND_LIST="add issue revoke"
case $COMMAND_LIST in
*"$COMMAND"*)
"$COMMAND" "$#"
;;
*)
helpFunction
echo "ERROR: Unknown command: $COMMAND"
exit 1
;;
esac
But that is of course only if your script supports commands/subcommands. Otherwise, it makes sense to error right away like you did, if there is an unknown parameter.