passing command output to variable

Infernal211283 · 01-11-2006, 03:05 AM

Hi,

I tried a lot of ways to pass values to some variable i made up and it works partially, i can successfully do

TIME=12:55
printf $TIME

and to get the output '12:55', but i can't pass an output of a command 'hwclock' to the variable.. i tried 'TIME=$hwclock', 'TIME=hwclock' 'hwclock > TIME'
'$hwclock > TIME' but those wont work as i need them to.

How can i accomplish this?

T.Hsu · 01-11-2006, 03:11 AM

Quote:

Command Substitution
Command substitution allows the output of a command to replace the command itself. Command substitution occurs when a command is enclosed as follows:

$(command)

or

`command`

Bash performs the expansion by executing command and replacing the command substitution with the standard output of the command, with any trailing newlines deleted. Embedded newlines are not deleted, but they may be removed during word splitting. The command substitution $(cat file) can be replaced by the equivalent but faster $(< file).
When the old-style backquote form of substitution is used, backslash retains its literal meaning except when followed by `$', ``', or `\'. The first backquote not preceded by a backslash terminates the command substitution. When using the $(command) form, all characters between the parentheses make up the command; none are treated specially.
Command substitutions may be nested. To nest when using the backquoted form, escape the inner backquotes with backslashes.
If the substitution appears within double quotes, word splitting and filename expansion are not performed on the results.

Quoted from bash (1)

Infernal211283 · 01-11-2006, 03:26 AM

Quote:

Originally Posted by T.Hsu

When using the $(command) form, all characters between the parentheses make up the command; none are treated
specially.

executing 'TIME=$(hwclock)' worked partially, i mean, the output of the command is usually 'Wed 11 Jan 2006 11:17:44 AM IST -0.928094 seconds' but the value $TIME stored is only 'Wed' - the [space] between 'Wed' and '11' broke the string that was supposed to be in the variable which shouldn't happen according to the above, should it?

T.Hsu · 01-11-2006, 03:34 AM

The problem is printf, use echo instead or printf %b "$(hwclock)" "\n"

Infernal211283 · 01-11-2006, 03:41 AM

Superb!

echoing showed:

echo $TIME
Wed 11 Jan 2006 11:35:02 AM IST -0.263685 seconds

printfing showed:

printf %b $TIME
Wed11Jan200611:35:02AMIST-0.263685seconds

Exactly what i needed,

Thank you.

Infernal211283 · 01-11-2006, 04:04 AM

ah, damn, guess it was to good to be true...

wanted to use it in a script like 'touch $TIME' to create files named as TIME's content but it wont work...

[root@fedint _tEsTiNg_]# touch $TIME
touch: invalid option -- 0
Try `touch --help' for more information.

:x

Infernal211283 · 01-11-2006, 04:17 AM

being slow i can now say that i figured out that the error is because the file cannot be created with ':', so i turned to alternative command 'date' using it's formats (%y.%m.%d), now it all works, sorry for odd questions.

I appreciate you for your help.

T.Hsu · 01-11-2006, 04:19 AM

double quotes

touch "$TIME"

Infernal211283 · 01-11-2006, 04:35 AM

^ thanks..

T.Hsu · 01-11-2006, 04:37 AM

Glad it helps. You may also try "touch -- $TIME" to see the results

Infernal211283 · 01-11-2006, 04:52 AM

Useful spamming command

[root@fedint 1]# echo $TIME
Wed 11 Jan 2006 11:35:02 AM IST -0.263685 seconds
[root@fedint 1]# touch -- $TIME
[root@fedint 1]# ll
total 36
-rw-r--r-- 1 root root 0 Jan 11 12:48 -0.263685
-rw-r--r-- 1 root root 0 Jan 11 12:48 11
-rw-r--r-- 1 root root 0 Jan 11 12:48 11:35:02
-rw-r--r-- 1 root root 0 Jan 11 12:48 2006
-rw-r--r-- 1 root root 0 Jan 11 12:48 AM
-rw-r--r-- 1 root root 0 Jan 11 12:48 IST
-rw-r--r-- 1 root root 0 Jan 11 12:48 Jan
-rw-r--r-- 1 root root 0 Jan 11 12:48 seconds
-rw-r--r-- 1 root root 0 Jan 11 12:48 Wed

marozsas · 01-11-2006, 05:26 AM

Just to enrich your learning about shell.
In general, the long format for date isn't useful for scripts and so. May be you prefer a more compact form of time. Something like this:
miguel@gold:~> date +%Y%m%d-%H%M%S
20060111-092317

so...
miguel@gold:~>FILENAME=$(date +%Y%m%d-%H%M%S)
miguel@gold:~>touch $FILENAME

or better yet:
miguel@gold:~>touch $(date +%Y%m%d-%H%M%S)

regards,

Infernal211283 · 01-11-2006, 05:54 AM

yep, just what i thought after i saw how files look if they're named after 'hwclock', i'm already trying to make a script using all this neat knowledge, hopefully i'll manage to create something intelligent.