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I'd like to pass input from a shell command over to a python script in an alias that uses a shell command.

test.py:

import sys
print(sys.argv)

the alias

alias foo='echo $(python test.py $1)'

since $ python cd_alias_test.py hello would print all the args: ['test.py', 'hello'] I'd expect this alias to do the same. However its stdout is

['test.py'] hello

Which means that the input string is being passed to stdin and not the script's arguments.

How I achieve the intended effect?

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2 Answers 2

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alias test='echo $(python test.py $1)'

$1 is not defined in an alias, aliases aren't shell functions; they're just text replacement; so your test hello gets expanded to echo $(python test.py ) hello, which gets expanded to echo ['test.py'] hello.

If you want a shell function, write one! (and don't call your function or alias test, that name is already reserved for the logical evaluation thing in your shell).

function foo() { echo $(python test.py $1) }
foo hello

But one really has to wonder: Why not simply make test.py executable (e.g. chmod 755 test.py) and include the #!/usr/bin/env python3 first line in it? Then you can just run it directly:

./test.py hello darkness my old friend
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  • Functionally speaking echo $(thing) could/should just be thing -- otherwise there's a risk of echo interpreting the output of thing as switches it should care about, e.g. echo $(printf "%s" "-n hello") ; echo world
    – bxm
    Jun 23 at 10:50
  • @bxm that might be the intention here! Jun 23 at 11:07
  • I understand how functions are more appropriate for this task, but I'm still a little confused as to how arguments like $1 are not defined in an alias. For instance if I have alias foo='python cd_alias_test.py $1', then the output for $ foo hello will be ['cd_alias_test.py', 'hello'] Jun 23 at 18:21
  • they're simply... not defined. There's nothing setting up a variable called $1, because an alias gets expanded to its value as if you just typed that in. So, your foo hello looks like you typed in python cd_alias_test.py $1 hello and that gets expanded to python cd_alias_test.py hello before execution. There's really no magic here. Just your assumption about what an alias does being a bit wrong, it seems! An alias doesn't take "arguments". An alias simply doesn't "exist" as programming construct: it gets replaced by its value before anything gets defined, expanded… Jun 23 at 18:23
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Your question is confusingly worded, but I seems you just want to execute an alias passing a parameter to your script.

I think this is what you want.

alias runtest='python test.py'

As otherwise mentioned, shell functions can be preferable to aliases -- allowing for less trivial arg handling.

So in this example:

function runtest() { python test.py "$1" ; }

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