Replace all regex matches in a file

Question

Consider a basic regex like a(.+?)a. How can one replace all occurences of that regex in a file with the content of the first group?

This python tutorial site might be helpful: http://pythontesting.net/python/regex-search-replace-examples/ — Mr-IDE, Jun 13 '19 at 09:29

score 5 · Accepted Answer · edited Jun 19 '20 at 16:50

5

Use can use the re module to use regular expressions in python and the fileinput module to simply replace text in files in-place

Example:

import fileinput
import re

fn = "test.txt" # your filename

r = re.compile('a(.+?)a')
for line in fileinput.input(fn, inplace=True):
  match = r.match(line)
  print match.group() if match else line.replace('\n', '')

Before:

hello this
aShouldBeAMatch!!!!! and this should be gone
you know

After:

hello this
aShouldBeAMa
you know

Note: this works because the argument inplace=True causes input file to be moved to a backup file and standard output is directed to the input file, as documented under Optional in-place filtering.

edited Jun 19 '20 at 16:50

Jon-Eric

16,458
8
63
96

answered Aug 10 '12 at 08:46

sloth

95,484
19
164
210

3

As a note to anyone who may be confused, `print` statements within that for loop are redirected to the file. (The [documentation](http://docs.python.org/library/fileinput.html) for `fileinput` is quite good). – David Cain Aug 10 '12 at 08:50
1

This works as intented, although im using `r.sub()` on the line to keep the non-matched parts of the line. – Sebastian Hoffmann Aug 10 '12 at 09:16
what is line.replace('\n', '') doing?? Where is the replacement text? Please explain your code – john ktejik Dec 14 '21 at 22:39

score 0 · Answer 2 · answered Aug 10 '12 at 08:50

0

You can use Notepad++ with Version >= 6.0. Since then it does support PCRE Regex.

You can then use your regex a(.+?)a and replace with $1

answered Aug 10 '12 at 08:50

stema

85,585
19
101
125

He asked about doing it in Python – kohane15 Feb 21 '21 at 05:04

David Cain · Answer 3 · 2012-08-10T09:27:05.237

-3

sed

Are you limited to using Python tools? Because sed works very well.

$ sed -i <filename> "s/a(.+?)a/\1/g"

Vim

In a Vim window, give the following search-and-replace ex command:

:%s/\va(.+?)a/\1/g

Note that many regex characters are escaped in Vim- \v sets "very magic" mode, which removes the need for escaping. The same command with "magic" (the default) is :%s/a\(.\+\?)a/\1/g

Python

If you're looking to do this in Python, BigYellowCactus' answer is excellent (use the re module for regex, and fileinput to modify the file).

edited Aug 10 '12 at 09:27

answered Aug 10 '12 at 08:38

David Cain

15,340
11
64
73

No, im Not but restricted to Windows. – Sebastian Hoffmann Aug 10 '12 at 08:42
@Paranaix, you have [options to run `sed` on Windows](http://stackoverflow.com/a/127567/815632). Alternatively, you could perform a search and replace in Vim. – David Cain Aug 10 '12 at 08:46

Replace all regex matches in a file

3 Answers3

sed

Vim

Python