Using back-ticks in Python subprocess
I want to run this git command through a Python script and get the output of it:
git diff --name-only mybranch `git merge-base mybranch develop`
The purpose of the command is to see what changes have been made on
mybranch since the last merge with develop.
- Git diff is complaining, “external diff died, stopping at … ” with my python diff program
- subprocesses from apache returning exit code -6 with not stdout or stderr
- Respond to git command line prompt from Python program
- Git add through python subprocess
- Can't get stdout/stderr from (Python) subprocess.check_output()
- Executing python subprocess via git hook
To achieve this I’m using
output = subprocess.Popen(["git", "diff", "--name-only", "mybranch", "`git merge-base mybranch develop`"], stdout=subprocess.PIPE, shell=True)
However, this does not work. The variable
output.communicate() simply gives me a printout of git usage — essentially telling me the input command is wrong.
I saw that a similar question exists here, but it only told me to use
shell=True which didn’t solve my problem.
I also attempted to run the two commands in succession, but that gave me the same output as before. It is possible that I am missing something in this step, though.
Any help or tips are appreciated.
2 Solutions collect form web for “Using back-ticks in Python subprocess”
Backticks and subprocess
The backtick being a shell feature, you may not have a choice but to use
shell=True, however pass in a shell command string, not a list of args
So for your particular command (assuming it works in the first place)
process = subprocess.Popen("git diff --name-only mybranch `git merge-base mybranch develop`", stdout=subprocess.PIPE, shell=True)
Notice when you call
Popen() you get a process, shouldn’t be called
Here’s a simple example that works with backticks
>>> process = subprocess.Popen('echo `pwd`', stdout=subprocess.PIPE, shell=True) >>> out, err = process.communicate() >>> out '/Users/bakkal\n'
Or you can use the $(cmd) syntax
>>> process = subprocess.Popen('echo $(pwd)', stdout=subprocess.PIPE, shell=True) >>> out, err = process.communicate() >>> out '/Users/bakkal\n'
Here’s what did NOT work (for backticks)
>>> process = subprocess.Popen(['echo', '`pwd`'], stdout=subprocess.PIPE, shell=True) >>> out, err = process.communicate() >>> out '\n' >>> process = subprocess.Popen(['echo', '`pwd`'], stdout=subprocess.PIPE, shell=False) >>> out, err = process.communicate() >>> out '`pwd`\n'
On POSIX, the argument list is passed to
/bin/sh -c i.e., only the first argument is recognized as a shell command i.e., the shell runs
git without any arguments that is why you see the usage info. You should pass the command as a string if you want to use
shell=True. From the
On POSIX with
shell=True, the shell defaults to
string, the string specifies the command to execute through the shell.
This means that the string must be formatted exactly as it would be
when typed at the shell prompt. This includes, for example, quoting or
backslash escaping filenames with spaces in them. If
sequence, the first item specifies the command string, and any
additional items will be treated as additional arguments to the shell
itself. That is to say,
Popendoes the equivalent of:
Popen(['/bin/sh', '-c', args, args, ...])
You don’t need
shell=True in this case.
#!/usr/bin/env python from subprocess import check_output merge_base_output = check_output('git merge-base mybranch develop'.split(), universal_newlines=True).strip() diff_output = check_output('git diff --name-only mybranch'.split() + [merge_base_output])