Python as a shell replacement

Posted Dec 13, 2019 17:23 UTC (Fri) by BenHutchings (subscriber, #37955)
In reply to: Python as a shell replacement by marcH
Parent article: Creating Kubernetes distributions

I also use "set -e" by habit, but it doesn't do exactly what you probably want. When you check the result of a command, that completely suppresses its effect inside the command. For example:

set -e
f() {
    false
    echo "continued"
}
f || echo "failed"

prints:

continued

Python as a shell replacement

Posted Dec 13, 2019 22:59 UTC (Fri) by marcH (subscriber, #57642) [Link] (1 responses)

Yes, set -e is absolutely not a silver bullet. It does not catch all errors, so you must lower your expectations. It does catch many of them, which has saved me and many others a lot of time, routinely, for years.

Some influent and vocal experts seem to have decided that, short of catching "all errors", catching "no error" is better than "many errors". I've read all their essays and I still couldn't make sense of their logic https://mywiki.wooledge.org/BashFAQ/105

"Works for us".

PS: besides 105 and a couple others, https://mywiki.wooledge.org/BashFAQ is the best.

Python as a shell replacement

Posted Dec 14, 2019 0:08 UTC (Sat) by karkhaz (subscriber, #99844) [Link]

I occasionally use a combined shell script/makefile if I care about catching errors on each command:

#!/bin/sh
# vim:set syntax=make:set ft=make:

MAKEFILE_START_LINE=$(\
  grep -nre makefile_starts_here "$0" \
  | tail -n 1 \
  | awk -F: '{print $1}')

TMP=$(mktemp)
tail -n+${MAKEFILE_START_LINE} "$0" > "${TMP}"

make -f "${TMP}"
SUCCESS=$?

rm -f "$TMP"
exit "$SUCCESS"

makefile_starts_here:
	command-1
	command-2
	command-3

This prints out everything below and including "makefile_starts_here" to a Makefile and then runs make on it, executing the commands one at a time. This is especially nice if I want built-in parallelism etc, it's actually even better than just using the shell (just ensure to print out "MAKEFLAGS=-j" at the top of the file).