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?
1 Answer
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.
answered Nov 20, 2012 at 20:00
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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?– XsiCommented Nov 20, 2012 at 20:07
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The standard streams are not arguments, they are streams provided to the program. Commented Nov 20, 2012 at 20:09
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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))– XsiCommented Nov 20, 2012 at 20:09
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equery -q uses
equery -q files '*'bash: /usr/bin/equery: Argument list too long equery -q usesxargs equery -q files '*'– XsiCommented Nov 27, 2012 at 4:31 -
grep SMTH <(CMD)instead ofgrep SMTH $(CMD)? cause first one is really close toCMD | grep SMTH.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 directgrep