Capturing git command output with subprocess

Question

I'm trying to return all git commit hashes for commits that contain 'As delivered' in their commit message. Essentially, I want to capture the output of the below git command:

git log --all -i --grep 'As Delivered' --format='%H'

The above git command runs as I expect it to in the command line, returning one matched hash per output line. Here's the code I'm trying to use to accomplish my goal:

def getHashesMatchingGrep(grepStr="As Delivered"):
    grep_option = '--grep=\'' + grepStr + '\''
    format_option = '--format="' + '%H' + '"'
    cmd = ['git', 'log', '--all', '-i', grep_option, format_option]
    print("Using command: " + str(cmd))
    process = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
    stdout, stderr = process.communicate()
    #return namedtuple('Std', 'out, err')(process.stdout.read(), process.stderr.read())
    return process.returncode, stdout, stderr

code, out, err = getHashesMatchingGrep()
print('code = {}\nout = {}\nerr = {}'.format(code, out, err))

But all I get as output from this is:

Using command: ['git', 'log', '--all', '-i', "--grep='As Delivered'", '--format="%H"']
code = 0
out = b''
err = b''

I've also tried defining text=True, and shell=True for my Popen call. In this case I get 'None' from err, but still no other output. If I edit my function so that cmd=['git','log','--all'] I get something, but still, why won't it return anything when I add the --grep line? I know if I type the same git command (with grep) in the cmd terminal I get results.

Am I not understanding how subprocess is supposed to work? It seems to run OK, but if it is failing, why aren't I getting the stderr? I'm very confused, please help!

I will add that git is installed and in my windows cmd path. — Daniel Crisp
– Daniel Crisp, Commented Feb 22, 2022 at 21:50
maybe it finds nothing in repo and you get empty output. Did you test command git log --all -i --grep 'As Delivered' --format='%H' directly in console? When I run it in console on some my repo then it gives me empty output. — furas
– furas, Commented Feb 22, 2022 at 23:26
This isn't a Git issue: --subprocess without --shell means you don't want to add quotes. — torek
– torek, Commented Feb 23, 2022 at 9:28

Daniel Crisp · Accepted Answer · 2022-02-22 22:18:45Z

3

It appears I hadn't 'tokenized' my cmd array appropriately.
Before:

grep_option = '--grep=\'' + grepStr + '\''
format_option = '--format="' + '%H' + '"'
cmd = ['git', 'log', '--all', '-i', grep_option, format_option]

After:

format_option = '--format="' + '%H' + '"'
cmd = ['git', 'log', '--all', '-i', '--grep', grepStr, format_option]

answered Feb 22, 2022 at 22:18

Daniel Crisp

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5 Comments

torek Over a year ago

Or just the literal '--format="%H"', since your string constants add up to that. You probably really just wanted '--format=%H' though, without the double quotes, just as you didn't really want the double quotes in your --grep. Note that git log with --format=%H is generally best converted to git rev-list, though, if at all possible.

Daniel Crisp Over a year ago

@torek Yeah, I thought about using rev-list but I'm not as familiar with it. That grep is important, will rev-list output allow me to grep on commit messages? I also advanced the way I'm doing this to -p --follow filename, I don't know if rev-list allows for that

torek Over a year ago

git rev-list and git log are sister commands, where rev-list is the plumbing variety and log is the porcelain one. Unfortunately, they're not quite twin sisters. If you want --follow you are forced to use git log, which respects user configuration, which is a real problem. Someone is trying to add a log.graph setting and it's breaking gitk and others that use git log as porcelain, when they would like to use git log as plumbing.

torek Over a year ago

(The --grep stuff is supported by git rev-list, but --follow isn't.)

Daniel Crisp Over a year ago

Interesting, thanks for the extra details, I appreciate it!

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