I implemented all builtins first, thinking I could use them as needed in my pipes.
I tried to mesh that in with the prev eg. which you gave of the IPC via pipes. But then I need to create 2 versions of my builtins,
if the builtin is the 1st command in the pipe, it's executed in the same shell,
if the builtin is somewhere in the middle,
then it needs to be executed in a separately forked process => that the builtin needs to have a corresponding external command for exec to work.
i.e
Code:
if( piped commands)
{
if(isbuiltin())
{
execbuiltin() // function where i implemented all builtins.
squirt into the first pipe
}
else
{
exec as in your sample prev.
(here it fails as that code would need me to exec an external command always - which may or may not exist)
}
}
Hi,
Can the cd command be invoked using pipes???
My actual question is slightly different. I am trying to run an executable from different folders and the path of these folders are obtained dynamically from the front end. Is there a way in which i can actually run the executable... (2 Replies)
Hi...Can anyone please guide me on FIFO Pipes in UNIX.I have lerant things like creating fifo pipes,using them for reads and writes etc.I want to know what is the maximum amount of memory that such a pipe may have? Also can anyone guide me on where to get info on this topic from? (4 Replies)
This is something I've given a lot of thought to and come up with no answer.
Say you have a data stream passing from a file, through process A, into process B. Process A only modifies a few bytes of the stream, then prints the rest of the stream unmodified. Is there any way to stream the file... (4 Replies)
im trying to figure out how to do the following:
using pipes to combine grep and find commands to print all lines in files that start with the letter f in the current directory that contain the word "test" for example?
again using pipes to combine grep and find command, how can I print all... (1 Reply)
I am really new to UNIX and programming in general and so apologies if this thread is a bit simple.
I have searched and found a piece of sample code for a training program I am currently undertaking, but seeing as I am relatively new, I dont completely understand how it works.
Here is the... (1 Reply)
I am really new to UNIX and programming in general and so apologies if this thread is a bit simple.
I have searched and found a piece of sample code for a training program I am currently undertaking, but seeing as I am relatively new, I dont completely understand how it works.
Here is the... (6 Replies)
Hello all, I am trying to learn more about programming Unix pipes in C.
I have created a pipe that does od -bc < myfile | head
Now, I am trying to create od -bc < myfile | head | wc
Here is my code, and I know I might be off, thats why I am here so I can get some clarification.
#include... (1 Reply)
Use and complete the template provided. The entire template must be completed. If you don't, your post may be deleted!
1. The problem statement, all variables and given/known data:
Create a pipe to show the number of people who are logged into the system right now.
Create a pipe to show... (2 Replies)
Discussion started by: lakers34kb
2 Replies
LEARN ABOUT BSD
popen
POPEN(3) Library Functions Manual POPEN(3)NAME
popen, pclose - initiate I/O to/from a process
SYNOPSIS
#include <stdio.h>
FILE *popen(command, type)
char *command, *type;
pclose(stream)
FILE *stream;
DESCRIPTION
The arguments to popen are pointers to null-terminated strings containing respectively a shell command line and an I/O mode, either "r" for
reading or "w" for writing. It creates a pipe between the calling process and the command to be executed. The value returned is a stream
pointer that can be used (as appropriate) to write to the standard input of the command or read from its standard output.
A stream opened by popen should be closed by pclose, which waits for the associated process to terminate and returns the exit status of the
command.
Because open files are shared, a type "r" command may be used as an input filter, and a type "w" as an output filter.
SEE ALSO pipe(2), fopen(3S), fclose(3S), system(3), wait(2), sh(1)DIAGNOSTICS
Popen returns a null pointer if files or processes cannot be created, or the shell cannot be accessed.
Pclose returns -1 if stream is not associated with a `popened' command.
BUGS
Buffered reading before opening an input filter may leave the standard input of that filter mispositioned. Similar problems with an output
filter may be forestalled by careful buffer flushing, for instance, with fflush, see fclose(3S).
Popen always calls sh, never calls csh.
7th Edition May 15, 1985 POPEN(3)