A bash function that runs script

Question

I'm trying to write a bash function named myrun, such that doing

myrun script.py

with a Python file:

#MYRUN:nohup python -u script.py &
import time
print 'Hello world'
time.sleep(2)
print 'Once again'

will run the script with the command specified in the first line of the file, just after #MYRUN:.

What should I insert in .bashrc to allow this? Here is what I have now:

myrun () {
[[ "1ドル" = "" ]] && echo "usage: myrun python_script.py" && return 0
<something with awk here or something else?>
}

• Ignacio Vazquez-Abrams: That sounds like an awful lot of work just to avoid writing a second script...
• Ed Morton: Hang on - you want to write a bash function that calls an awk script when called from python? Doesn't that sound a teeny bit like you might be going off the rails?
• Basj: @EdMorton: No, not called from Python. Called from bash with myrun script.py.
• Ed Morton: So it's a python script that calls awk when it's called from bash? That's not any better.
• Score_Under: @Basj You can! As an example, if you don't see --no-fork on the command line, you could do: subprocess.Popen(['nohup', sys.executable, sys.argv[0], '--no-fork'] + sys.argv[1:]); exit(). (I'd advise you check that --no-fork works before following this example though, or you'll end up with a process that keeps spawning then dying).

Answer 1

A minimalist version:

$ function myrun {
 [[ "1ドル" = "" ]] && echo "usage: myrun python_script.py" && return
 local cmd=$(head -n 1 < "1ドル" | sed s'/# *MYRUN://')
 $cmd
}
$ myrun script.py
appending output to nohup.out
$ cat nohup.out
Hello world
Once again 
$

(It's not clear to me whether you're better off using eval "$cmd" or simply $cmd in the last line of the function, but if you want to include the "&" in the MYCMD directive, then $cmd is simpler.)

With some basic checking:

function myrun {
 [[ "1ドル" = "" ]] && echo "usage: myrun python_script.py" && return
 local cmd=$(head -n 1 <"1ドル")
 if [[ $cmd =~ ^#MYRUN: ]] ; then cmd=${cmd#'#MYRUN:'}
 else echo "myrun: #MYRUN: header not found" >&2 ; false; return ; fi
 if [[ -z $cmd ]] ; then echo "myrun: no command specified" >&2 ; false; return; fi
 $cmd # or eval "$cmd" if you prefer
}

• Basj: Thanks! Maybe we should add something to make $cmd empty if #MYRUN: is not found... Currently it would try to run the first line anyway!
• Score_Under: If your command is specified with shell syntax, it may be cleaner to use eval "$cmd" rather than just $cmd (which has totally different rules for how the command is parsed).
• Charles Duffy: I'd argue that the eval approach will always be more desirable. See BashFAQ #50 -- mywiki.wooledge.org/BashFAQ/050 -- for a discussion of the pitfalls in the other approach (quotes are treated as literal data, spaces can't possibly be escaped, etc).

Answer 2

This is unrelated to Bash. Unfortunately, the shebang line cannot portably contain more than a single argument or option group.

If your goal is to specify options to Python, the simplest thing is probably a simple sh wrapper:

#!/bin/sh
nohup python -u <<'____HERE' &
.... Your Python script here ...
____HERE

• Charles Duffy: I'd argue that even simpler than this would be to do nohup's work in native Python; it's not that hard to reopen the standard FD set and set signal-handling behavior for HUP.