Add the Current Date to a Filename from the Command Line

Published: February 14, 2018

Tags:

Shell

Something I do very often is add the current date to a filename from the command line.

Historically, I’ve always done something like this…

$ mv foo.txt 2018_02_14_18_07_foo.txt

It always felt dirty though…why should I manually type out the current date when I’m sitting in front of a computer which is equally if not more capable of doing that exact thing?

While I long put off researching this, today, I finally turned to Google in hopes of finding a more sane approach.

Googling

My search quickly brought me to the “How to append date to backup file” Stack Overflow question. There I found the following suggestion…

$ touch "foo.backup.$(data +%F_%R)"

While this is an improvement in one sense in that it eliminates the need to manually type out the current date, it is a step backwards in another in that it requires me to remember the proper bash syntax and time format to get the desired result.

There has to be a better way…

Functions + ~/.bashrc to the rescue

Fortunately, there was. Bash allows you define custom functions in a dotfile in your home directoy called .bashrc. Any functions defined there will be available whenever you open a terminal window.

NOTE: If you're using zsh, you can do the same with ~/.zshrc

I’ve leveraged this feature to define a custom function which I’ve called add-date which automatically adds the date to the filename of the given file (in my preferred format).

Here’s what I’ve added the following to my ~/.bashrc.

function add-date {
    mv $1 "$(date +%Y%m%d_%H%M%S)_$1"
}

NOTE: After making edits to your ~/.bashrc (or ~/.zshrc) you need to run source ~/.bashrc (or source ~/.zshrc) for the edits to take effect for the terminal window you currently have open.

Now I can simply run the add-date command and pass it a file and it will automatically add the date for me….

$ touch foo.txt
$ ls
foo.txt
$ add-date foo.txt
$ ls
20180214_182223_foo.txt

Feel free to use or modify as needed (e.g. if you prefer a different date format).