641
My heart goes out to shell programmers who have to support posix sh (lemmy.world)
submitted 5 months ago by [email protected] to c/[email protected]
95 comments fedilink hide all child comments

Explanation for newbies:

  • Shell is the programming language that you use when you open a terminal on linux or mac os. Well, actually "shell" is a family of languages with many different implementations (bash, dash, ash, zsh, ksh, fish, ....)

  • Writing programs in shell (called "shell scripts") is a harrowing experience because the language is optimized for interactive use at a terminal, not writing extensive applications

  • The two lines in the meme change the shell's behavior to be slightly less headache-inducing for the programmer:

    • set -euo pipefail is the short form of the following three commands:
      • set -e: exit on the first command that fails, rather than plowing through ignoring all errors
      • set -u: treat references to undefined variables as errors
      • set -o pipefail: If a command piped into another command fails, treat that as an error
    • export LC_ALL=C tells other programs to not do weird things depending on locale. For example, it forces seq to output numbers with a period as the decimal separator, even on systems where coma is the default decimal separator (russian, dutch, etc.).

  • The title text references "posix", which is a document that standardizes, among other things, what features a shell must have. Posix does not require a shell to implement pipefail, so if you want your script to run on as many different platforms as possible, then you cannot use that feature.

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[-] [email protected] -2 points 5 months ago* (last edited 5 months ago)

just use python instead.

  • wrap around subprocess.run(), to call to system utils
  • use pathlib.Path for file paths and reading/writing to files
  • use shutil.which() to resolve utilities from your Path env var

Here's an example of some python i use to launch vscode (and terminals, but that requires dbus)


from pathlib import Path
from shutil import which
from subprocess import run

def _run(cmds: list[str], cwd=None):
    p = run(cmds, cwd=cwd)

    # raises an error if return code is non-zero
    p.check_returncode()

    return p

VSCODE = which('code')
SUDO   = which('sudo')
DOCKER = which('docker')

proj_dir = Path('/path/to/repo')

docker_compose = proj_dir / 'docker/'

windows = [
  proj_dir / 'code',
  proj_dir / 'more_code',
  proj_dir / 'even_more_code/subfolder',
]
for w in windows:
  _run([VSCODE, w])

_run([SUDO, DOCKER, 'compose', 'up', '-d'], cwd=docker_compose)
[-] [email protected] 10 points 5 months ago

Cool, now pipe something into something else

[-] [email protected] 1 points 5 months ago* (last edited 5 months ago)

that is a little more complicated

p.communicate() will take a string (or bytes) and send it to the stdin of the process, then wait for p to finish execution

there are ways to stream input into a running process (without waiting for the process to finish), but I don't remember how off the top of my head


from shutil import which
from subprocess import Popen, PIPE, run
from pathlib import Path

LS   = which('ls')
REV  = which('rev')

ls   = run([LS, Path.home()], stdout=PIPE)

p = Popen([REV], stdin=PIPE, stdout=PIPE)
stdout, stderr = p.communicate(ls.stdout)

print(stdout.decode('utf-8'))
[-] [email protected] 1 points 5 months ago

Or Rust. Use Command::new() for system commands and Path::new() for paths.

this post was submitted on 15 Jan 2025
641 points (98.2% liked)

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