Grep and Python

Question

I need a way of searching a file using grep via a regular expression from the Unix command line  For example when I type in the command line   python pythonfile py  RE   file-to-be-searched    I need the regular expression  RE  to be searched in the file and print out the matching lines   Here s the code I have   import re import sys  search term   sys argv 1  f   sys argv 2   for line in open f   r        if re search search term  line           print line          if line    None              print  no matches found    But when I enter a word which isn t present  no matches found doesn t print

User · Answer

Adapted from a grep in python   Accepts a list of filenames via  2    does no exception handling      usr bin env python import re  sys  os  for f in filter os path isfile  sys argv 2         for line in open f  readlines            if re match sys argv 1   line               print line   sys argv 1  resp sys argv 2   works  if you run it as an standalone executable  meaning   chmod  x   first

User · Answer

Concise and memory efficient      usr bin env python   file  grep py import re  sys  map sys stdout write  l for l in sys stdin if re search sys argv 1  l      It works like egrep  without too much error handling   e g    cat input-file   grep py  RE    And here is the one-liner   cat input-file   python -c  import re sys map sys stdout write  l for l in sys stdin if re search sys argv 1  l      RE

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You might be interested in pyp  Citing my other answer         The Pyed Piper   or pyp  is a linux command line text manipulation   tool similar to awk or sed  but which uses standard python string and   list methods as well as custom functions evolved to generate fast   results in an intense production environment

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You can use python-textops3   from textops import    print   n  join cat f    grep search term     with python-textops3 you can use unix-like commands with pipes

User · Answer

use sys argv to get the command-line parameters use open    read   to manipulate file use the Python re module to match lines

User · Answer

The natural question is why not just use grep   But assuming you can t     import re import sys  file   open sys argv 2    r    for line in file       if re search sys argv 1   line            print line    Things to note    search instead of match to find anywhere in string comma     after print removes carriage return  line will have one  argv includes python file name  so variables need to start at 1   This doesn t handle multiple arguments  like grep does  or expand wildcards  like the Unix shell would   If you wanted this functionality you could get it using the following   import re import sys import glob  for arg in sys argv 2        for file in glob iglob arg           for line in open file   r                if re search sys argv 1   line                   print line

User · Answer

The real problem is that the variable line always has a value  The test for  no matches found  is whether there is a match so the code  if line    None   should be replaced with  else

[python] Grep and Python

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