How to Do Sed Like Text Replace With Python

How to do sed like text replace with python?

massedit.py (http://github.com/elmotec/massedit) does the scaffolding for you leaving just the regex to write. It's still in beta but we are looking for feedback.

python -m massedit -e "re.sub(r'^# deb', 'deb', line)" /etc/apt/sources.list

will show the differences (before/after) in diff format.

Add the -w option to write the changes to the original file:

python -m massedit -e "re.sub(r'^# deb', 'deb', line)" -w /etc/apt/sources.list

Alternatively, you can now use the api:

>>> import massedit
>>> filenames = ['/etc/apt/sources.list']
>>> massedit.edit_files(filenames, ["re.sub(r'^# deb', 'deb', line)"], dry_run=True)

python search/replace regex with sed-like expression

My first thoughts were just to split it by / and pass it as args to re.sub.

Turns out this is rather complicated and as I'm pretty sure its not bulletproof, so I give you this as a starting point.

Thing is, what if we want to deal with slashes, as in replace slashes with backslashes. Then the sed expression will be

's/\\/\//g'

I have to split it by slash that is not preceded by backlash

_, pattern, repl, options = re.split(r'(?<!\\)/', sed)

To make it more complicated, the shash can be preceded by two backslashes, so:

_, pattern, repl, options = re.split(r'(?<![^\\]\\)/', sed)

And re.sub will look like

re.sub(pattern, repl, s, count='g' not in options)

Ups, no, in Python, slash doesn't have to be escaped, so:

re.sub(pattern, re.sub(r'\\/', '/', repl), s, count='g' not in options)

---

>>> import re
>>> s = r'\some\windows\path'
>>> sed = r's/\\/\//g'
>>> _, pattern, repl, options = re.split(r'(?<![^\\]\\)/', sed)
>>> re.sub(pattern, re.sub(r'\\/', '/', repl), s, count='g' not in options)
'/some/windows/path'

Replace a string in a python script and execute the script

You sound like you know how to use commandline arguments, but just for the sake of completion, for those who read this question in the future and are not sure how to go about using command line arguments with python:

One easy quick way to receive commandline arguments in your code is to use the argv property of the sys module which is a list that contains all arguments sent to the script. When a python file is called, the first argument captured by sys.argv is the name of the script itself. Any commandline arguments are captured afterwards:

import sys
arguments = sys.argv
# make sure user really sent an argument, or else set it to some default value
if len(arguments)>1:
    desired_string = arguments[1]
else:
    desired_string = "Some_default_value"

How to search and replace text in a file?

fileinput already supports inplace editing. It redirects stdout to the file in this case:

#!/usr/bin/env python3
import fileinput

with fileinput.FileInput(filename, inplace=True, backup='.bak') as file:
    for line in file:
        print(line.replace(text_to_search, replacement_text), end='')

sed to python replace extra delimiters in a

You may read the file line by line, split with tab, and if there are more than 3 items, join the items after the 3rd one with _tab_:

lines = []
with open('inputfile.txt', 'r') as fr:
    for line in fr:
        split = line.split('\t')
        if len(split) > 3:
            tmp = split[:2]                      # Slice the first two items
            tmp.append("_tab_".join(split[2:]))  # Append the rest joined with _tab_
            lines.append("\t".join(tmp))         # Use the updated line
        else:
            lines.append(line)                   # Else, put the line as is

See the Python demo

The lines variable will contain something like

Mike    -3,434.09   testing_tab_testing_tab_123
Mike    -3,434.09   testing_tab_256
No  operation   here

Replace strings and update file using sed from python

To use > redirection you need to use shell=True and a single string argument, not a list.

subprocess.call("""sed 's/"A"|"B"|"C"/A|B|C/g' inputfile.txt > outputfile.txt""", shell=True)

How to replace multiple lines in file in Python using sed

You have to create a raw string to prevent python from parsing the input string before passing it on the OS call.

The below example illustrates this

Your input string is

sed -i -e '/NATOMS/c\NATOMS     5   -1.10\n hi\nbye' sedinp.txt

Now assign it to a variable and print it

>>> normalcmd="sed -i -e '/NATOMS/c\NATOMS     5   -1.10\n hi\nbye' sedinp.txt"
>>> print normalcmd
sed -i -e '/NATOMS/c\NATOMS     5   -1.10
 hi
bye' sedinp.txt
>>> 

As you see, the escape sequences have been parsed.

Now create a raw string.

>>> rawcmd=r"sed -i -e '/NATOMS/c\NATOMS     5   -1.10\n hi\nbye' sedinp.txt"
>>> print rawcmd
sed -i -e '/NATOMS/c\NATOMS     5   -1.10\n hi\nbye' sedinp.txt
>>> 

You can see that the escape sequences are not parsed.

Now use it in the os call.

>>> os.system(rawcmd)
0
>>> 

Hope this helps.

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