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Full Discussion: Problems understanding pipes
Top Forums Programming Problems understanding pipes Post 302562727 by Corona688 on Friday 7th of October 2011 10:20:58 PM
Old 10-07-2011
Are you checking for builtins after you fork? Smilie You should check before. The whole point is that builtins don't need fork at all since they can happen wholly inside the shell.

I don't understand why you'd be using builtins in the middle of a pipe chain in the first place. They don't work there in csh. Unless you're trying to build in things like cat, which I don't think is a good idea.

Of course external commands must exist to use external commands. What's wrong with that? Smilie
 

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filter_create_fd(3)						   util/filter.h					       filter_create_fd(3)

NAME
filter_create_fd - Create a sub process and return the requested pipes SYNOPSIS
#include <util/filter.h> NEOERR *filter_create_fd(const char *cmd, int *fdin, int *fdout, int *fderr, pid_t *pid); ARGUMENTS
cmd -> the sub command to execute. Will be executed with /bin/sh -c fdin -> pointer to return the stdin pipe, or NULL if you don't want the stdin pipe fdout -> pointer to return the stdout pipe, or NULL if you don't want the stdout pipe fderr -> pointer to return the stderr pipe, or NULL if you don't want the stderr pipe DESCRIPTION
filter_create_fd and filter_create_fp are what popen been: a mechanism to create sub processes and have pipes to all their input/output. The concept was taken from mutt, though python has something similar with popen3/popen4. You control which pipes the function returns by the fdin/fdout/fderr arguments. A NULL value means "don't create a pipe", a pointer to an int will cause the pipes to be created and the value of the file descriptor stored in the int. You will have to close(2) the file descriptors yourself. RETURN VALUE
fdin -> the stdin file descriptor of the sub process fdout -> the stdout file descriptor of the sub process fderr -> the stderr file descriptor of the sub process pid -> the pid of the sub process SEE ALSO
filter_wait(3), filter_create_fp(3), filter_create_fd ClearSilver 12 July 2007 filter_create_fd(3)
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