this post was submitted on 15 Jan 2025
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    My heart goes out to shell programmers who have to support posix sh (lemmy.world)
    submitted 2 days ago by [email protected] to c/[email protected]
    96 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] 9 points 1 day ago (1 children)

    Cool, now pipe something into something else

    [–] [email protected] 1 points 1 day ago* (last edited 1 day 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'))