I had a list of items I wanted to sort in a non-standard way:

app-function1.site1.jeppson.org
app-function2.site3.jeppson.org
app-function3.site4.jeppson.org
app-function4.site2.jeppson.org
app-function1.site6.jeppson.org
app-function3.site9.jeppson.org
app-function4.site7.jeppson.org

It’s a generalized list for publication but you get the idea. I wanted to sort by site name. Thanks to this post I found it’s relatively easy. You can tell the sort command to use a character as a tab delimiter (-t) and then specify which key “column” to sort by (-k)

In my case I sorted by site by specifying the dot character '.' as the delimiter, and the second “column” as the key '-k2'

The end result was this:

cat apps-by-site-unsorted.txt | sort -t. -k2

app-function1.site1.jeppson.org
app-function4.site2.jeppson.org
app-function2.site3.jeppson.org
app-function3.site4.jeppson.org
app-function1.site6.jeppson.org
app-function4.site7.jeppson.org
app-function3.site9.jeppson.org

Success