A shell script to swap the contents of two files.

Sometimes you accidentally create two files whose contents you need to exchange:

$ echo "Hello!" > ko; echo "안녕하세요!" > en
$ cat en ko
안녕하세요!
Hello!

Oops! en should have the English text, and ko the Korean text. Using twiddle, we can fix this:

$ twiddle en ko
$ cat en ko
Hello!
안녕하세요!

A common mistake in this situation is to run mv en ko; mv ko en. This overwrites the contents of ko, permanently deleting the data Hello! and causing an error in the second command.

The correct solution is to use a temporary file: mv en tmp; mv ko en; mv tmp ko. twiddle is a failsafe shorthand for this sequence of steps. It checks that both files exist, creates a temporary file safely (using mktemp) in the /tmp/ directory to guard against overwriting files and certain kinds of snooping attacks, and then performs the exchange operation.

Put the contents of twiddle.sh into a file twiddle somewhere on your path. You could use the following two commands:

$ sudo curl "https://raw.githubusercontent.com/maxkapur/twiddle/main/twiddle.sh" -o /usr/local/bin/twiddle
$ sudo chmod +x /usr/local/bin/twiddle

The first command copies the contents of twiddle.sh to the file /usr/local/bin/twiddle. The second command grants permission to execute the /usr/local/bin/twiddle as a program.

Contributions and bug reports are welcome. I have only tested this script on Ubuntu 22.04 and Ubuntu Server 22.04.