Ever find yourself with a browser tab opened to Advanced Bash Scripting, writing obtuse Bash code to do something that would take you 4 seconds in Python? Yeah, me too.

Python in Bash Scripts (PBS) is an experimental replacement for your everyday bash scripts that gives you the good features of Bash (easy command calling, easy piping) with the power and flexibility of Python. The resulting code is a normal Python script that does Bash-like things easily.

Integrating

import pbs

Examples

Executing Commands

Commands work like you'd expect:

# print the contents of this directory 
print ls("-l")

Note that these aren't Python functions, these are running the binary commands on your system dynamically by resolving your PATH, much like Bash does.

longest_line = wc(__file__, "-L")

Keyword Arguments

Keyword arguments also work like you'd expect: they get replaced with the long-form commandline option:

# resolves to "curl http://duckduckgo.com/ -o page.html --silent"
curl("http://duckduckgo.com/", "-o page.html", silent=True)

# resolves to "add_user amoffat --system --shell=/bin/bash --no-create-home"
add_user("amoffat", system=True, shell="/bin/bash", no_create_home=True)

Piping

Piping has become function composition:

# sort this directory by biggest file
print sort(du(glob("*"), "-sb"), "-rn")

# print the number of folders and files in /etc
print wc(ls("/etc", "-1"), "-l")

Finding Commands

"Which" finds the full path of a program, or returns None if it doesn't exist. This command is one of the few commands implemented as a Python function, and therefore doesn't rely on the "which" program actually existing.

print which("python") # "/usr/bin/python"
print which("ls") # "/bin/ls"
print which("some_command") # None

if not which("supervisorctl"): apt_get("install", "supervisor", "-y")

You can also use the return argument of "which" as the program:

etc_files = str(which("ls")("/etc", "-1")).split()

Environment Variables

Environment variables are available globally much like they are in Bash:

print HOME
print SHELL
print PS1

Exceptions

Exceptions are dynamically generated based on the return code of the command. This lets you catch a specific return code, or catch all error return codes through the base class ErrorReturnCode:

try: print ls("/some/non-existant/folder")
except ErrorReturnCode_2:
    print "folder doesn't exist!"
    create_the_folder()
except ErrorReturnCode:
    print "unknown error"
    exit(1)

Commandline Arguments

You can access commandline arguments similar to Bash's $1, $2, etc by using ARG1, ARG2, etc:

print ARG1, ARG2

# if an argument isn't defined, it's set to None
if ARG10 is None: do_something()

You can access the entire argparse/optparse-friendly list of commandline arguments through "argv". This is recommended for flexibility:

import argparse
parser = argparse.ArgumentParser(prog="PROG")
parser.add_argument("-x", default=3, type=int)
ns = parser.parse_args(argv)
print ns.x

Background Processes

Commands can be run in the background with the special pbs_bg=True keyword argument:

# blocks
sleep(3)
print "...3 seconds later"

# doesn't block
p = sleep(3, pbs_bg=True)
print "prints immediately!"
p.wait()
print "...and 3 seconds later"

You can also pipe together background processes!

p = wc(curl("http://github.com/", silent=True, pbs_bg=True), "--bytes")
print "prints immediately!"
print "byte count of github: %d" % int(str(p).strip()) # lazily completes

bothra90/pbs