Have you ever needed to change the file extension for every file in the current directory but didn't want to have to manually do it for every file? Well, ask no more!

Bash:

Rename File With Extension:

for file in *.old; do
    mv "$file" "$(basename "$file" .old).new"
done

Delete File With Extension:

for file in *.old; do
    rm "$file"
done

Replace All Occurrences In Files With Extension:

for file in *.old; do
    sed -i 's/replaceMe/replaceWith/g' $file
done

Replace All Occurrences In All Files:

for file in *.*; do
    sed -i 's/replaceMe/replaceWith/g' $file
done

Python:

Rename File With Extension:

import os, sys

for filename in os.listdir():
    if not os.path.isfile(filename): continue
    newname = filename.replace('.old', '.new')
    os.rename(filename, newname)

Delete File With Extension:

import os, sys

for filename in os.listdir():
    if not os.path.isfile(filename): continue
    if not filename.endswith(".old"): continue
    os.remove(filename)

Replace All Occurrences In Files With Extension:

import os, sys

for filename in os.listdir():
    if not os.path.isfile(filename): continue
    if not filename.endswith(".old"): continue
    f = open(filename, "r")
    contents = f.read()
    f.close()
    contents = contents.replace("replaceMe", "replaceWith")
    f = open(filename, "w")
    f.write(contents)

Replace All Occurrences In All Files:

import os, sys

for filename in os.listdir():
    if not os.path.isfile(filename): continue
    f = open(filename, "r")
    contents = f.read()
    f.close()
    contents = contents.replace("replaceMe", "replaceWith")
    f = open(filename, "w")
    f.write(contents)

In all of these, replace .old and .new with the file extensions of your choice, and with the replace all occurrences of replaceMe with replaceWith in all files with .old file extension, replace replaceMe and replaceWith with the text of your choice