cat grep and cut - translated to python

Question

maybe there are enough questions and or solutions for this  but I just can t help myself with this one question  I ve got the following command I m using in a bash-script   var   cat   filename    grep  something    cut -d    -f2        Now  because of some issues I have to translate all the code to python  I never used python before and I have absolutely no idea how I can do what the postet commands do  Any ideas how to solve that with python

User · Answer

You need a loop over the lines of a file, you need to learn about string methods

with open(filename,'r') as f:
    for line in f.readlines():
        # python can do regexes, but this is for s fixed string only
        if "something" in line:
            idx1 = line.find('"')
            idx2 = line.find('"', idx1+1)
            field = line[idx1+1:idx2-1]
            print(field)

and you need a method to pass the filename to your python program and while you are at it, maybe also the string to search for...

For the future, try to ask more focused questions if you can,

User · Answer

In Python  without external dependencies  it is something like this  untested    with open  filename   as origin      for line in origin          if not  something  in line             continue         try              print line split      1          except IndexError              print

User · Answer

you need to use os system module to execute shell command  import os os system  command     if you want to save the output for later use  you need to use subprocess module  import subprocess child   subprocess Popen  command  stdout subprocess PIPE shell True  output   child communicate   0

User · Answer

You need to have better understanding of the python language and its standard library to translate the expression                                  cat   filename   Reads the file cat   filename  and dumps the content to stdout     pipe redirects the stdout from previous command and feeds it to the stdin of the next command  grep  something   Searches the regular expressionsomething plain text data file  if specified  or in the stdin and returns the matching lines     cut -d    -f2  Splits the string with the specific delimiter and indexes splices particular fields from the resultant list  Python Equivalent  cat   filename     with open   filename   r   as fin           Read the file Sequentially                        for line in fin                            ----------------------------------------------------------------------------------- grep  something    import re                                   The python version returns                    line   re findall r something   line  0     a list of matches  We are only                                                                interested in the zero group ----------------------------------------------------------------------------------- cut -d    -f2      line   line split      1                    Splits the string and selects                                                                the second field  which is                                                                index 1 in python    Combining  import re with open  filename   as origin file      for line in origin file          line   re findall r something   line          if line             line   line 0  split      1          print line

User · Answer

For Translating the command to python refer below -  1 Alternative of cat command is open refer this  Below is the sample   gt  gt  gt  f   open  workfile    r    gt  gt  gt  print f   2 Alternative of grep command refer this  3 Alternative of Cut command refer this

[python] cat, grep and cut - translated to python

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