Change files extension in a directory

A onliner

for f in *.old; do mv "$f" "${f%.old}.new";  done

How???

To change the name of a file on Linux/Unix use the mv command

mv currentfilename newfilename

If there is a file named aleemisiaka.old and want to rename to aleemisiaka.new

We can store the filename to a variable with export FILENAME=aleemisiaka

And use the variable name in the mv command

mv "$FILENAME"$ "$FILENAME.new"

This renames the file from aleem-isiaka.old to aleemisiaka.old.new

To ensure we end up with aleemisiaka.new and not aleemisiaka.old.new we could use parameter expansion.

echo "${FILENAME%.old}" would give just aleemisiaka without the old.

Now append the new extension with echo "${FILENAME%.old}.new" which gives aleemisiaka.new

Awesome

Back to mv command

mv "$FILENAME}" "${FILENAME.old}.new"

Renames the file from aleemisiaka.old to aleemisiaka.new.

To replace all files in a directory use the Bash for loop

for f in *.old # Loops through all the files with the .old extension
do
  mv "$f" "${f%.old}.new" # renames from file.old to file.new
done

# a oneliner
for f in *.old; do mv "$f" "${f%.old}.new";  done

Au revoir