Find and Replace Text Across Multiple Files in Bash

#!/bin/bash

# Configuration
SEARCH_DIR="."           # Directory to start the search (e.g., '.', './src')
FILE_EXTENSION="php"     # File extension to target (e.g., 'html', 'js', 'css', '*')
OLD_STRING="old_function_name" # The string to find
NEW_STRING="new_function_name" # The string to replace with

echo "Searching for '$OLD_STRING' and replacing with '$NEW_STRING' in files with .$FILE_EXTENSION extension within '$SEARCH_DIR'..."

# Use find to locate files and sed to perform the replacement
# -type f: Only consider files
# -name "*.$FILE_EXTENSION": Match files with the specified extension
# -exec ... +: Execute the command for multiple found files at once
# sed -i: Perform in-place editing (create backup with -i.bak if supported/desired)
# 's/old/new/g': Substitution command: 's'ubstitute 'old' with 'new', 'g'lobally (all occurrences on line)
find "$SEARCH_DIR" -type f -name "*.$FILE_EXTENSION" -exec sed -i "s/$OLD_STRING/$NEW_STRING/g" {} +

if [ $? -eq 0 ]; then
    echo "Replacement completed successfully."
else
    echo "An error occurred during replacement. Check logs."
fi

# Important Note: sed -i on macOS behaves differently than GNU/Linux.
# On macOS, `sed -i ''` will edit in-place without backup.
# `sed -i '.bak'` will create backup files.
# For cross-platform compatibility, consider using `perl -pi -e 's/OLD/NEW/g' filenames`
# or ensure you have GNU sed installed (e.g., `brew install gnu-sed` on macOS).