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
29/07/11

4
By: xakon
2011-07-29 12:47:26

2 Alternatives + Submit Alt

What Others Think

Very nice!
flatcap · 583 weeks and 5 days 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 · 583 weeks and 4 days 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 · 583 weeks and 4 days ago
I like how eval works with the stat's -s option.
putnamhill · 582 weeks and 6 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 · 582 weeks and 6 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 · 582 weeks and 5 days ago
Multiple variable assignments from command output in BASH are the main heading and you all can now order assignment online in case you are busy with other stuff and want professionals to help you out with your academics tasks today. Try this out as it will be of great aid for us.
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rahimhh21 · 5 weeks and 4 days 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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