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Full Discussion: difference bewteen pipe, xargs, and exec
Top Forums Programming difference bewteen pipe, xargs, and exec Post 302563933 by Corona688 on Wednesday 12th of October 2011 12:28:55 PM
Old 10-12-2011
First off, exec is nothing like the first two. exec does a variety of things from executing a command without returning(the shell is replaced by the new command), as well as opening/closing files.

pipes transfer the output of one program into the input of another. Without the pipe or redirection, they'd be trying to read from your keyboard and trying to print to your screen, but you can feed them data from any source and send their output anywhere you like. Shell utilities are intended to be flexible that way.

Code:
# useless example
echo asdf | cat

'echo' prints to standard output, 'cat' reads from standard input, the pipe joins them together so 'asdf' is read by cat and printed.

But what about this:

Code:
# This won't print anything
echo something | echo

echo does not read from standard input, it takes commandline parameters and nothing but parameters. So how do we translate from pipe into that?

This is what xargs is for.
Code:
echo a b c d | xargs command

is equivalent to command a b c d. Whenever you need to translate from a pipe or file into commandline arguments, xargs serves.

Code:
# This prints 'something' into xargs' input, causing xargs to run 'echo something'.
echo something | xargs echo

---------- Post updated at 10:28 AM ---------- Previous update was at 10:26 AM ----------

If you post some code which is confusing you, I'll try to explain it.
This User Gave Thanks to Corona688 For This Post:
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LEARN ABOUT SUNOS

print

print(1)							   User Commands							  print(1)

NAME

       print - shell built-in function to output characters to the screen or window

SYNOPSIS

   ksh
       print [ -Rnprsu [n]] [arg...]

DESCRIPTION

   ksh
       The shell output mechanism. With no flags or with flag - or -, the arguments are printed on standard output as described by echo(1).

OPTIONS

       The following options are supported:

       -n	       suppresses new-line from being added to the output.

       -R

       -r	       (raw  mode) ignore the escape conventions of echo. The -R option will print all subsequent arguments and options other than
		       -n.

       -p	       causes the arguments to be written onto the pipe of the process spawned with |& instead of standard output.

       -s	       causes the arguments to be written onto the history file instead of standard output.

       -u [ n ]        flag can be used to specify a one digit file descriptor unit number n on which the output will be placed. The default is 1.

EXIT STATUS

       The following exit values are returned:

       0	Successful operation.

       >0	Output file is not open for writing.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       echo(1), ksh(1), attributes(5)

SunOS 5.10							    15 Apr 1994 							  print(1)
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