Everybody knows about using !! to add sudo to your previous command, but there are a couple other things I constantly use it for. So this is just a little PSA in case it never occured to you:

1. grep results

Say I want to search a bunch of files for a string, and then open all files containing that string in my editor.

I want to check the search results first, and I never get the exact search correct on my first try anyway, so I'll run a series of commands that might look like...

grep -rn . -e "mystring"
...
grep -rn . -e "my.\?string"
...
grep -Rni . -e "my.\?string"
...

Checking the results each time, until I have exactly the set of files that I want.

Here's the trick: now add the "-l" flag to grep to get just the file paths:

grep -Rnil . -e "my.\?string"

Now when you use !!, you'll get all those filenames. Therefore we can just do vim -p $(!!) to get all those files opened in tabs in vim.

2. with which

Sometimes I want to read or edit a script that's on my computer.

To find it, I run which some-command. This confirms that it exists under that name, and that it's an actual script and not an alias or shell function.

Now, we can just use vim $(!!) or cat $(!!) or whatever to open it.