Another example of using diff on two process substitutions I did this morning. I've been quarantining some files from various paths that all have unique basenames into a single directory. I have a CSV file listing the original path in the first field followed by some other metadata. I wanted to compare the files in the CSV file ("quarantined-files.csv") to the files I had moved into the "quarantine" subdirectory. I came up with this:

    diff <(cut -d, -f1 quarantined-files.csv |xargs -L1 basename |sort) <(ls ./quarantine/ |sort)

(Yes, the listing from "ls" comes out sorted, but it's always possible it'll sort certain characters a bit differently than "sort" does depending on locale settings, aliases, etc, etc. Piping both outputs through "sort" should ensure the same sorting collation in all cases.)

It took me a while to really grok this sort of thing, but once it clicked, it's often the first thing I think of. Basically any time you might be tempted to dump something to a temporary file, you should ask yourself "can I use process substitution?"