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Full Discussion: Fork and Execvp Not Executing Bash Commands From C correctly.
Top Forums Programming Fork and Execvp Not Executing Bash Commands From C correctly. Post 302969174 by bakunin on Saturday 19th of March 2016 04:16:24 AM
Old 03-19-2016
To expand on what Don Cragun already said:

A commandline like

Code:
command1 | command2

is not "a process" but in fact the shell creates two such processes: one for "command1", one for "command2". You need to execute the procedure of using execvp() or fork() for both of them because both are processes in their own right. Only then you need a provision for the pipeline functionality.

A (shell-) pipeline is to connect STDOUT of the one process to the STDIN of the other. But this means there are already two process-environments with such file descriptors that can be connected. Here is a thread that might give you the picture: Trouble with pipes in chat client on linux.

I hope that helps.

bakunin
This User Gave Thanks to bakunin For This Post:
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LEARN ABOUT OPENSOLARIS

libbash

LIBBASH(7)							  libbash Manual							LIBBASH(7)

NAME

     libbash -- A bash shared libraries package.

DESCRIPTION

     libbash  is  a package that enables bash dynamic-like shared libraries. Actually its a tool for managing bash scripts whose functions you may
     want to load and use in scripts of your own.

     It contains a 'dynamic loader' for the shared libraries ( ldbash(1)), a configuration tool (ldbashconfig(8)), and some libraries.

     Using ldbash(1) you are able to load loadable bash libraries, such as getopts(1) and hashstash(1).  A bash shared library that can be  loaded
     using
     ldbash(1) must answer 4 requirments:

     1.     It must be installed in $LIBBASH_PREFIX/lib/bash (default is /usr/lib/bash).

     2.     It must contain a line that begins with '#EXPORT='.  That line will contain (after the '=') a list of functions that the library
	    exports.  I.e. all the function that will be usable after loading that library will be listed in that line.

     3.     It must contain a line that begins with '#REQUIRE='.  That line will contain (after the '=') a list of bash libraries that are
	    required for our library.  I.e. every bash library that is in use in our bash library must be listed there.

     4.     The library must be listed (For more information, see ldbashconfig(8)).

   Basic guidelines for writing library of your own:
     1.     Be aware, that your library will be actually sourced. So, basically, it should contain (i.e define) only functions.

     2.     Try to declare all variables intended for internal use as local.

     3.     Global variables and functions that are intended for internal use (i.e are not defined in '#EXPORT=') should begin with:
		  __<library_name>_
	    For example, internal function myfoosort of hashstash library should be named as
		  __hashstash_myfoosort
	    This helps to avoid conflicts in global name space when using libraries that come from different vendors.

     4.     See html manual for full version of this guide.

AUTHORS

     Hai Zaar <haizaar@haizaar.com>
     Gil Ran <ril@ran4.net>

SEE ALSO

     ldbash(1), ldbashconfig(8), getopts(1), hashstash(1) colors(1) messages(1) urlcoding(1) locks(1)

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