Parameter expansion to loop over pairs: ${a%b} and ${a#b}

[karmag]

Hey, a command line community? That's a pretty neat thing to have.

So to introduce myself, here's something I figured out pretty recently. It's in one of those eyes-glazing-over parts of the shell man page (but I had a specific problem to solve so I had to figure it out). Behold! It is a piece of "parameter expansion" magic:

$ TEST='foo:bar' ; echo ${TEST%:*} ${TEST#*:}
foo bar

Ooh, exciting! No wait, it's not. But here's the problem I had: How can I loop over pairs of values in a script or one-liner?

The solution I came up with looked something like this:

$ for f in url1:filename1 url2:filename2 url3:filename3;
do URL=${f%:*}; FILENAME=${f#*:} ;
...
; done

...and so for each pair, URL and FILENAME gets set to their respective portion. (And you'll be glad to learn that I got my Youtube-mediated crime drama fix in the end.)

Comments

[foxfirefey]

Ooooh I did not know this and it is useful!