Multiple variable assignments from command output in BASH

eval $(date +"day=%d; month=%m; year=%y")
It's quite easy to capture the output of a command and assign it in a shell's variable: day=$(date +%d) month=$(date +%m) But, what if we want to perform the same task with just one program invocation? Here comes the power of eval! date(1) outputs a string like "day=29; month=07; year=11" (notice the semicolons I added on purpose at date's custom output) which is a legal shell line. This like is then parsed and executed by the shell once again with the help of eval. Just setting 3 variables! Inspired by LinuxJournal's column "Dave Taylor's Work the Shell".
Sample Output
$ eval $(date +"day=%d; month=%m; year=%y")
$ echo $day/$month/$year

By: xakon
2011-07-29 12:47:26

2 Alternatives + Submit Alt

What Others Think

Very nice!
flatcap · 540 weeks and 1 day ago
Using 'eval' in any language makes me nervous. Still, even a curmudgeon like me can see how useful it is to treat instructions as data and vice-versa.
Mozai · 540 weeks ago
Not strangely, I have the same feelings about 'eval' in almost every language. Yet, I totally agree with you as I re-discover once again its power and the usefulness of going around the wall when it stands in front of you while trying to solve a problem! And by the way, I should not forget the power of 'eval' in many Lisp-like languages!
xakon · 540 weeks ago
I like how eval works with the stat's -s option.
putnamhill · 539 weeks and 2 days ago
How do you mean? Can you please provide an example of your point? stat(1) doesn't have a '-s' switch in my system!
xakon · 539 weeks and 2 days ago
I see what you mean. I don't have that option on my linux systems either. Maybe it's just a BSD thing. This is how it works on my mac: stat -s some.file st_dev=234881026 st_ino=3657562 st_mode=0100644 st_nlink=1 st_uid=501 st_gid=20 st_rdev=0 st_size=478 st_atime=1312497217 st_mtime=1309535724 st_ctime=1309535724 st_birthtime=1309535658 st_blksize=4096 st_blocks=8 st_flags=0 When you eval the output of stat -s (if you have that option), you get a bunch of variables set.
putnamhill · 539 weeks and 1 day ago

What do you think?

Any thoughts on this command? Does it work on your machine? Can you do the same thing with only 14 characters?

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