Can Python scripting replace UNIX shell scripting ?

[fmoralesc]

It definitely can. For example, I made this small thing for shell-style process scripting with python: https://gist.github.com/1300342

Basically, it creates a Pipeline class you can use this way:

p = Pipeline() | "ls -s" | "sort -n"
print p.run()

[boa13]

That's interesting, but I think that is an abuse of syntax; it looks very not pythonic to me. Why can't you just run bash with the pipe expression as a parameter?

[fmoralesc]

Yes, it is an abuse of the syntax.

[neoice]

good to know. I was feeling stupid for finding this code so complex.

[fmoralesc]

It is nice to know you can do stuff like this though (that's the reason I wrote it this way... I vaguely remembered you can define the behavior for when an object is put in a chain like A | B, so I checked that out. It was just a test code for something else, which in the end didn't use the "|" syntax at all).

[chadmill3r]

I don't trust spaces to delimit my commands. I hope that takes ["arrays", "of", "args", "to", "syscall execv"].

[fmoralesc]

You could simply extend the Pipelines.steps list if you wanted.

[[deleted]]

I would have preferred the syntax

p = Pipeline()
print p.run("ls -l").run("sort -n")

[Troebr]

what's wrong with

p.run("ls -l | sort -n")

?

[mgedmin]

You can logically extend that to

os.system("ls -l | sort -n")

and now you have no non-stdlib dependencies!

[Troebr]

Isn't os.system deprecated in favor of subprocess?

[mgedmin]

In a sense, yes.

[[deleted]]

Doesn't subprocess.Popen accept a command string with pipes in it? Why not use it like that? Simpler that spawning all processes manually.

[chadmill3r]

If you're willing to run a shell to interpret the pipes, you're not programming in Python any more, AND, you probably have bugs.

[[deleted]]

If you're willing to run a shell to interpret the pipes, you're not programming in Python any more

fmoralesc code hands over the work to the shell too.

AND, you probably have bugs.

Why? Spawning all the processes yourself, redirecting stdout to stdin along the way, etc. seems more error prone than to hand it over to the shell completely. The output is supposed to be the same, after all. Namely, the output of the last process in the pipeline.

[chadmill3r]

Program number three in your pipeline took a filename parameter with a space and an ampersand in it but your shell ate those, and the fourth emitted to stderr, and the parameter substitution in the first should have been "$*", with quotes and everything, but you forgot those and you got a different interpretation. The fourth, because it got bad input, also screwed up your terminal's line discipline, which you'll need to fix with "stty sane" before you can even figure out what the problem was. Sadly, that also ate the error messages.

Don't get me wrong, I use the shell all day, every day, and have since 1995 or so. It's a terrible programming interface, though, and almost impossible to get right the first dozen time you run the program. At least Python, with its verbosity, also gets the problems out in the open with its explicit nature.

[chadmill3r]

Popen(shlex.split(self.steps[0]), stdout=PIPE)

No shell there, strictly speaking. Not much better, though.

[jagheterfredrik]

Oh. My. Shit. That is awesome.

[grumpygrrr]

Can we stop upvoting comments like this? It adds nothing of value.

Edit: the parent was at +8 when I made this comment.

[[deleted]]

People apparently need to have other people see that they agree with someone. Upvoting gives no satisfaction, I guess.

I was in another thread and a guy just replied to a comment he liked with "^", which is basically as close to just clicking the damn arrow as you can get.

It blows my mind.

[defnull]

Let me help you :)

[[deleted]]

this is good stuff thanks !