No more unmaintainable error-prone Bash scripts - use this instead

better-than-bash-scripts.py

# Bash really should be avoided as much as possible (within reasonable limits, of course) even for one-liners which *seem* trivial.
# Bash is very error-prone by design. It's hard to comprehend all the pitfalls (e.g. https://mywiki.wooledge.org/BashFAQ/105)
# and it's a regrettable time-waste anyway.
#
# Modern Python is good for scripting the logic - keep Bash only for launching executables and most primitive
# pipes and redirections (avoid subshells, substitutions and so on). No need to install anything -
# just start your script with the following small self-contained helper function (check the examples for usage). Its features:
# * terminates on non-zero exit status by default
# * returns the output (combined - which usually should not be a problem - use e.g. '2>/dev/null' when it is)
# * prints commands and combined output
# * prepends 'set -o pipefail'
#
import subprocess, sys
def run (cmd: str, *args, check=True, pipefail=True, **kwargs):
	print('$', cmd, flush=True)
	if pipefail:
		cmd = 'set -o pipefail && ' + cmd
	#we want to be able to stream the output (use `echo test1; sleep 1; echo test2` to test)
	with subprocess.Popen(cmd, *args, shell=True, executable='/bin/bash', stdout=subprocess.PIPE, stderr=subprocess.STDOUT,
			bufsize=1, universal_newlines=True,  #'text' was added in 3.7
			**kwargs) as process:
		output = []
		for line in process.stdout:  #should not deadlock because stderr=subprocess.STDOUT
			print(line, end="")
			output.append(line)
		exit_status = process.wait()
	output = "".join(output).strip()
	if check and exit_status:
		# sys.exit(f"\n-------\n[ERROR] command failed: {cmd}")
		raise Exception(f"Command failed (see above): {cmd}")
	elif check:
		return output
	return exit_status, output


################## Usage examples:
var = "world"
run(f'echo "Hello, {var.capitalize()}!"')

try:
    run('cat non-existing-file')
except SystemExit:
    "expected"
else:
    raise Exception("will not happen")

result = run('echo $0')
assert result == '/bin/bash'

exit_status, result = run('whatever', check=False)
#^ alternatively a name like "err"/"error" may be more readable, e.g. "if err".
#When you don't care about any output, use it like this: "if run(...)[0]"

exit_status, _ = run('{ echo "auto-pipefail test"; false; } | grep test', check=False)
assert exit_status != 0