[Linux-disciples] xargs questions

[Adam Rosi-Kessel]

Stephen R Laniel wrote:
> On Thu, Nov 11, 2004 at 08:18:29AM -0500, Adam Rosi-Kessel wrote:
>> I'm not sure what it's doing in the tail command above, but the point of
>> xargs is *not* to create commands that fit on the command line--the point
>> is to take STDIN and convert it to arguments to a command.  It's
>> essential glue.
> If the command line could be arbitrarily long, why wouldn't
> we just use
> command1 `command2GeneratingInsanelyLongOutput`
> ?

First, it would often just be an annoying way to accomplish what you want.

You might have problems with nested backticks, quoting, etc..  One of 
the great things about xargs is you don't need to worry about internal 
escapes.  (It also works well with the -0 option, where your arguments 
are 'null' delimited, and then you don't have to worry about any odd 
characters).

But more importantly command1 `command2` is just not equivalent to 
command2 | xargs command1.  The first turns a *pipe* into arguments, and 
runs command1 repeatedly for each line of piped input.  The backtick 
example won't give the same results where the "insanely long output" is 
several unique lines.  Try it, you'll see.

You might also use xargs for odd things like, e.g., mkfifo.  You could 
have the output of a FIFO special file cat'd into xargs to be run as a 
command.  I suppose there's a way to do this with backticks in certain 
circumstances, but xargs seems much more graceful.
-- 
Adam Rosi-Kessel
http://adam.rosi-kessel.org
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