How can i invoke a shell command from python which includes regexp?

Question

How can I invoke a shell command from python which includes regexp (i.e., cat filename*).

I wrote:

pid = subprocess.Popen(["cat", filename + "*"])

but I am getting an error

cat filename* no such file or directory.

I'd like to force the shell to treat "*" as a regexp and not as a string. Is there any way to implement this?

What file do you want cat to open? Could you give an example? — fredley
– fredley, Commented Oct 21, 2011 at 15:32
i have a folder where i have splitted a file with name filaname in : filaneme00,filaename01,...filenamen. and i want afterwards to compose with this: cat filename*>filename_original_version — curious
– curious, Commented Oct 21, 2011 at 15:37

Kirk Strauser · Accepted Answer · 2011-10-21 15:31:33Z

6

Use an underlying shell to expand your globs:

pid = subprocess.Popen(["cat",filename+"*"], shell=True)

Alternatively, use glob.glob to expand your arguments before running the command:

import glob
pid = subprocess.Popen(["cat"] + glob.glob(filename + "*"))

answered Oct 21, 2011 at 15:31

Kirk Strauser

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Ahmed Masud · Accepted Answer · 2011-10-21 15:35:25Z

4

FIRST it's not regular expression it's shell expansion (glob) that you seem to want to execute. Which means that you should invoke /bin/sh to execute cat. The following should do the trick:

pid = subprocess.Popen(["/bin/sh", "-c", "cat", filename + "*"]);

Now /bin/sh will actually perform the asterisk expansion for you and you'll get the desired result.

Or you can use globbing library to do globbing expansions yourself (i.e. do the work that shell does):

pid = subprocess.Popen(["cat"] + glob.glob(filename + "*"));

glob.glob() returns the array of files that match the globbing.

answered Oct 21, 2011 at 15:35

Ahmed Masud

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4 Comments

curious Over a year ago

When i am using the glob.glob ( filename + "*" ) the files are not combined in alphabetical order as when you open the shell and type cat filename* . When i invoke a new shell i am getting this: cat: -: Input/output error. The same is happening with @Kirk's answers

kindall Over a year ago

Yes, glob uses the order the files are stored in the directory, which is not alphabetical. You could put sorted(...) around the glob.glob() call.

Kirk Strauser Over a year ago

Ahmed, the shell=True argument to Popen() accomplishes the same thing.

Ahmed Masud Over a year ago

Ah :-) Thanks for that... my python 2.x is weak. I started using it from 3.x

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