3 finger claw technique for POSIX shell programming. Three one-line functions which greatly enhance shell programming, enabling reliable UNIX-style programming in an extremely concise fashion.

try_or_die.sh

#!/bin/sh

##############################################################################
# This code known is distributed under the following terms:
# 
# Copyright (c) 2013 Isaac (.ike) Levy <ike@blackskyresearch.net>.
# All rights reserved.
# 
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
# 1. Redistributions of source code must retain the above copyright
#    notice, this list of conditions and the following disclaimer.
# 2. Redistributions in binary form must reproduce the above copyright
#    notice, this list of conditions and the following disclaimer in the
#    documentation and/or other materials provided with the distribution.
# 
# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
# SUCH DAMAGE.
##############################################################################
# Credits:
# William Baxter (safe/try pattern originator)
# Matthew Story (loads of use)
# okan@ (try refinements, config conventions)
# Allan Jude (try - the actual name)
##############################################################################

shout() { echo "$0: $*" >&2; }
die() { shout "$*"; exit 111; }
try() { "$@" || die "cannot $*"; }

# examples, using it
try cd /some/place
try tar xzvfp /another/place/stuff.tbz
# (you may not want to 'try' that tar, depending)

true
# alternatively, exit 0

I see your three fingers, and raise you five.

https://github.com/GIJack/bash_theory/blob/master/five_fingers.sh

Not quite as the UNIX Haiku like elegant, but more useful and produces better output

Hi @GIJack,

I read through your 5-fingers there, and they are not in any way related to the 3-fingr claw except that they are shell functions.

Your functions appear to be five common print-to-screen type patterns (which I assume you use quite regularly), yet the 3-finger-claw allows a user to fundamentally alter the behavior of a particular program.

Best,
.ike

that's a whole lot of copyright ordinance for a simple 3-line technique that has been widely used throughout the industry for a long long time.

shout() { echo "$0: $*" >&2; }
die() { shout "${@:2}"; exit $1; }
try() { "$@" || die $? "cannot $*"; }

echo 'About to true'
try true
echo 'About to mkdir fred'
try mkdir fred
echo 'About to mkdir fred'
try mkdir fred

outputs :

About to true
About to mkdir fred
mkdir: fred: File exists
a.sh: Cannot mkdir fred

This will track the actual exit code that caused the failure.

I think.

Hi @GIJack,

I read through your 5-fingers there, and they are not in any way related to the 3-fingr claw except that they are shell functions.

Your functions appear to be five common print-to-screen type patterns (which I assume you use quite regularly), yet the 3-finger-claw allows a user to fundamentally alter the behavior of a particular program.

Best, .ike

Not quite. Two of the functions are directly comparable

cry -> message, but sans $0, alllow the user to name his program whatever. also better formatted. At least you can put $(basename $0), or PROGNAME=$(basename $0) for added complexity, but that is just that.

there is also warn to handle soft errors.

exit_with_error() -> replacement for die(). The big improvement is that it takes exit code as a parameter. You have a hardcoded 111 as an exit code. That's a magic number. As well as hardcoded exit message.

I also do not use a try because its entirely superfluous in shell as you already have || that works as except, but doesn't need a try.

so you can

[ test ] && exit_with_error 1 "Program Shit the Bed"