= Simple filename timestamp
:categories: shell

When writing Jekyll posts or creating log files with dates on them, I usually
struggle with finding a direct way of accomplishing that.  There's a simple
solution: `date -I`.

[source,sh]
----
./my-program.sh > my-program.$(date -I).log
cp post-template.md _posts/$(date -I)-post-slug.md
----

Using this built-in GNU/Linux tool allows you to `touch $(date -I).md` to
readily create a `2020-08-12.md` file.

I always had to read `man date` or search the web over and over, and after doing
this repeatedly it became clear that both `date -I` and `date -Is` (`s` here
stands for seconds) are the thing that I'm looking for 95% of the time:

[source,sh]
----
# inside my-program.sh
echo "Program started at $(date -Is)"
# output is:
# Program started at 2020-08-12T09:04:58-03:00
----

Both date formats are hierarchical, having the bigger time intervals to the
left.  This means that you can easily sort them (and even tab-complete them)
with no extra effort or tool required.
