Today, I was helping a co-worker with a script. He needed to find some set of directories, add /*.jar to the end of each, and put them together in a single line as coma-separated values.
Enter paste! (Funny thought, typing 'man paste' into google turned out much better than I thought it would!)
Say we had a list of all the files on my RaspberryPi's home directory, and we wanted to put them together as a comma separated list... We would simply pipe them through paste with the --delimiters=, and --serial flags set.
$ ls ~/Desktop/ | paste -d, -s
Even though I've been using linux since about 2003, I feel like I stumble onto little nuggets like this pretty often!