Piping in bash using python

[Demasu]

I have a bash script that I want to import in to Python, mainly just to see if I can or not. However in the script I do use some piping of commands into sed to trim it down to what I need. When I tried doing it with the os.system() call, it didn't work. The exact error is

sed: -e expression #1, char 16: unterminated `s' command

However the command that was run can be run in bash without an error. Is there a better/another way to do this?

For reference the command is:

locate -n 1 wp-config.php | sed 's/wp-config.php/\n/g' | sed '/wp-config.php/ d' | sed '/^$/ d'

[tetsujin]

I have a bash script that I want to import in to Python, mainly just to see if I can or not. However in the script I do use some piping of commands into sed to trim it down to what I need. When I tried doing it with the os.system() call, it didn't work. The exact error is

However the command that was run can be run in bash without an error. Is there a better/another way to do this?

For reference the command is:

locate -n 1 wp-config.php | sed 's/wp-config.php/\n/g' | sed '/wp-config.php/ d' | sed '/^$/ d'

I think the issue here is that you have multiple quoting rules interacting. Like probably the invocation looks something like this:

os.system("locate -n 1 wp-config.php | sed 's/wp-config.php/\n/g' | sed '/wp-config.php/ d' | sed '/^$/ d'")

The problem is, having the whole command inside double quotes means that the usual rules for Python strings apply. For instance, try running this in Python:

print "a\nb"

Python interprets that string as 'a-newline-b'. So there's an actual newline character (instead of a bacslash-n) in your first sed command. sed doesn't like this, it sees the newline as a statement delimiter.

To get around this you can use r-quoting in python:

os.system(r"locate -n 1 wp-config.php | sed 's/wp-config.php/\n/g' | sed '/wp-config.php/ d' | sed '/^$/ d'")

The r"..." syntax turns off most of the usual special character syntax of the quoted string, so when you enter something like r"\n" the resulting string contains a backslash followed by 'n'.

[Demasu]

Thank you! I completely forgot about that (it's been a while since I used python). I never knew about the r option either with print. Thanks again!

[tetsujin]

Thank you! I completely forgot about that (it's been a while since I used python). I never knew about the r option either with print. Thanks again!

Well, it's not actually an option of print - it's an alternate syntax for string literals. If you use regular single or double quotes, you get a string that interprets backslash as part of a special character. String literals can have one or more prefix characters before the first quote: 'r' for raw strings, 'u' for Unicode.