sed

Examples

# For single file
sed 's/unix/linux/g' geekfile.txt

# For file type in directory (not saving)
for file in *md
do
  sed 's/html/md/' $file
done

# For file type in directory (saving)
for file in *md
do
  sed 's/html/md/' -i $file
done

Sources

• Sed Command in Linux/Unix with examples - GeeksforGeeks* linux - Environment variable substitution in sed - Stack Overflow