Take the 2-minute tour ×
Unix & Linux Stack Exchange is a question and answer site for users of Linux, FreeBSD and other Un*x-like operating systems.. It's 100% free, no registration required.

It's really important because intuitively they are all similar for me.

Could one realise that those two are really like one another for me, i.e. absolutely equal?

share|improve this question
    
I can't say why I don't understand. –  Xsi Nov 20 '12 at 19:58
    
did you mean grep SMTH <(CMD) instead of grep SMTH $(CMD)? cause first one is really close to CMD | grep SMTH. –  rush Nov 20 '12 at 20:32
4  
This is not a bad question, I would upvote it if only you please stopped spamming your own questions with so much confusion and - is it anger? Relax! You won't learn anything as all your energy will be wasted on being constantly on fire. –  Emanuel Berg Nov 20 '12 at 21:47
    
sorry, you were right. xi@localhost ~ $ grep SRC_URI $(find /usr/portage -name *.ebuild) | wc -l 25921 xi@localhost ~ $ cat $(find /usr/portage -name *.ebuild) | grep SRC_URI | wc -l 25921 - no difference, except for inclusion of filename with direct grep –  Xsi Nov 23 '12 at 12:16

1 Answer 1

They don't do the same thing at all. The former is command substitution, the latter is piping. The result is completely different.

grep foo "$(echo foo)" will look for the word "foo" in a file called "foo", because "foo" is the output from echo. echo foo | grep foo will look for the word "foo" from its STDIN input. In the former case, you'll probably get a file not found error. In the latter case, you won't. They're fundamentally not the same operation.

share|improve this answer
    
It might be simply didn't fit my mind cause I used to know there are 3 working principles: STDIN STDOUT STDERR. From your perspective I couldn't use pipe with any given command that I want to use. Because I must somehow know with what command work - 3 cases, or even more - with 4th case - with file. Surely I have mess in my head. I'm very unsure that help (man page) consist of such things as arguments. Are those - arguments, or I'm bad at terminology? –  Xsi Nov 20 '12 at 20:07
    
The standard streams are not arguments, they are streams provided to the program. –  Chris Down Nov 20 '12 at 20:09
    
Next moment, now It seems that I can't use $() because it is not at least as good in description as pipe (takes something from STDIN(OUT)) –  Xsi Nov 20 '12 at 20:09
    
equery -q uses equery -q files '*' bash: /usr/bin/equery: Argument list too long equery -q uses xargs equery -q files '*' –  Xsi Nov 27 '12 at 4:31
    
xargs equery -q uses equery -q files '*' –  Xsi Nov 27 '12 at 4:32

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.