Question

I’m trying to write an svn pre-commit hook in python. Part of this involves checking the diff file to see if there are any actual file changes (as opposed to just property changes).

I have a working grep command which I can execute fine on the shell

grep "^\(Added: \|Modified: \|Deleted: \)" diff filename | grep -v 'svn:'

However when I put it through subprocess.POpen it escapes all my backslashes, which knackers the regexp.

Executing command: ['grep', '"^\\Added: \\|Modified: \\|Deleted: \\)", ...]

How do I avoid this?

NB: I’m aware that I can pipe results between subprocesses and I can do the two greps that way. I need help getting the first one working first though :/

NB2: I also tried using filterdiff –clean instead and couldn’t get it to work. Searching for Added, Modified or Deleted lines, removing those with ‘svn:’ in and checking I had some results seemed to work though.

Python code:

command = ['grep', '"^\(Added: \|Modified: \|Deleted: \)"', filename]
sys.stdout.write('Executing command: %s\n' % (command))

p = subprocess.Popen(command,
stdin = subprocess.PIPE
stdout = subprocess.PIPE
stderr = subprocess.STDOUT
shell = True)
data = p.stdout.read()

if len(data) == 0:
    sys.stdout.write("Diff does not contain any file modifications./n")
    exit(0)

Answer 1

You need to consider what you want grep to see in its command line arguments.

The first argument needs to be the literal string "^\(Added: \|Modified: \|Deleted: \)", so that means that it shouldn’t include the double quotes but should include the backslashes.

The way to express this kind of string is to use Python raw strings:

command = ['grep', r'^\(Added: \|Modified: \|Deleted: \)', filename]

A good way to check what you’re actually running is to replace grep by echo so you can at least see what you’re passing to the command.