On Tue, Aug 30, 2022 at 07:28:43AM +0200, Laszlo Ersek wrote: > I had grepped the virt-p2v and virt-v2v shell scripts for shebangs: > > 1 #!/bin/sh > 2 #!/bin/bash > 4 #!/usr/bin/env perl > 17 #!/bin/bash - > > 1 #!/bin/bash > 1 #!/usr/bin/env python3 > 1 #!/usr/bin/sh > 5 #!/usr/bin/env perl > 67 #!/bin/bash - > > The thinking seems to have been that > - python3 and perl may "move", > - bash is considered always available.
For p2v, yeah, we are pretty much guaranteed to be running on Linux, and therefore have bash (even if /bin/sh is not bash). > > > >> + > >> +set -e -u -C > > > > My personal opinion is that 'set -e' is a crutch that should be > > avoided because of its unintended interaction with functions; > > Can you please elaborate? > > POSIX writes, "When a function is executed, it shall have the > syntax-error and variable-assignment properties described for special > built-in utilities in the enumerated list at the beginning of Special > Built-In Utilities", and I've checked that list -- I don't know what you > mean. Here's a good writeup: http://mywiki.wooledge.org/BashFAQ/105 One of the simplest demonstrations on that page: $ bash -c 'set -e; f() { set -e; false; echo huh; }; f; echo survived' $ bash -c 'set -e; f() { set -e; false; echo huh; }; f && echo survived' huh survived That is, using 'set -e' to end function f early "works", but ONLY in situations where f itself is not invoked in a context where 'set -e' is suppressed because of a conditional in an outer scope. And once 'if' or '&&' suppresses 'set -e', you cannot re-enable it within f itself. Context-sensitive behavior of your function body based on the context of the caller is NOT intuitive. That said, if you KNOW that -e behaves non-intuitively, and plan to write your script with that in mind, it can be helpful. The complaint is that because -e is disabled in so many situations, it is harder to prove that -e catches all the scenarios that you WANTED to be caught than it is to just write the error handling yourself. > > > but I'm > > not adamant enough about it to tell people to rip it out of scripts. > > For short scripts, like this one, it's easy enough to check that we > > aren't tripping over any of -e's surprises. > > > >> + > >> +disk= > >> + > >> +cleanup() > >> +{ > >> + set +e > >> + if test -n "$disk"; then > >> + rm -f -- "$disk" > >> + disk= > >> + fi > >> +} > >> + > >> +trap cleanup EXIT > > > > Is it intentional that you are not also cleaning up on signals like > > INT and HUP? > > Yes, as EXIT covers those. Okay; currently true enough for bash, but not portable to other shells. In fact, the Austin Group visited that topic just this week: https://austingroupbugs.net/view.php?id=621 After 2018 edition page 2420 line 77499 section 2.14 trap, add a new paragraph: The EXIT condition shall occur when the shell terminates normally (exits), and may occur when the shell terminates abnormally as a result of delivery of a signal (other than SIGKILL) whose trap action is the default. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3266 Virtualization: qemu.org | libvirt.org _______________________________________________ Libguestfs mailing list Libguestfs@redhat.com https://listman.redhat.com/mailman/listinfo/libguestfs
