Updating multiple lines of a text file python

Question

is there any way to update multiple lines of a textfile using python.I want to delete the data between two lines My text file is as follows

Project
Post
<cmd> ---Some statements--
  ---Some statements---
Mycommand "Sourcepath" "DestPath"
</cmd>
Post
Lib
TargetMachine=MachineX86
Lib
Project
Post
<cmd> ---Some statements---
  ---Some statements---
Mycommand "Sourcepath" "DestPath"
</cmd>
Post
Lib
TargetMachine=MachineX64
Lib

I want to delete everything between cmd tag.So that the resulting text file should be as follows

Project
Post
<cmd>
</cmd>
Post
Lib
TargetMachine=MachineX86
Lib
Project
Post
<cmd>
</cmd>
Post
Lib
TargetMachine=MachineX64
Lib

Tim Pietzcker · Accepted Answer · 2012-09-18 13:28:51Z

4

Assuming you can read the entire file into memory at once, I'd suggest

import re
with open("input.txt") as infile, open("output.txt", "w") as outfile:
    outfile.write(re.sub(r"(?s)<cmd>.*?</cmd>", "<cmd>\n</cmd>", infile.read()))

To only match tags that have xcopy in them, you need to expand the regex a little:

import re
with open("input.txt") as infile, open("output.txt", "w") as outfile:
    outfile.write(re.sub(
        r"""(?sx)<cmd>      # Match <cmd>.
        (?:                 # Match...
         (?!</cmd>)         #  (unless we're at the closing tag)
         .                  #  any character
        )*                  # any number of times.
        \bxcopy\b           # Match "xcopy" as a whole word
        (?:(?!</cmd>).)*    # (Same as above)
        </cmd>              # Match </cmd>""", 
        "<cmd>\n</cmd>", infile.read())

edited Sep 18, 2012 at 13:28

answered Sep 18, 2012 at 13:12

Tim Pietzcker

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5 Comments

mystack Over a year ago

thank you tim for your Quick response what to do if i want to delete the data between cmd only if it contain 'xcopy' string

pR0Ps Over a year ago

Note that this won't properly process nested <cmd> tags, but it doesn't look you need to so it should be fine.

mystack Over a year ago

Hi Tim Pietzcker one more doubt.For some case i have to match XCOPY.ie i have to do above process for both XCOPY and xcopy.I tried with re.IGNORECASE but it didn't worked

Tim Pietzcker Over a year ago

Use (?isx) instead of (?sx) at the start of the regex.

mystack Over a year ago

ohh great you are really a regex guru.Thank you.If you don't mind please suggest some topics for regex

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