I'm not sure I'm following what is going on here, but I think you want something more like:
This assumes that yuv4mpeg_to_v4l2 is reading data from standard input and feeding it into your display device while mplayer is converting tom_and_jerry.mp4 into a format that yuv4mpeg_to_v4l2 reads and directs its output to the file named by the -vo yuv4mpeg:file=pathname option's option argument.
It also assumes that mplayer does not write anything to its standard output (and that nothing else inside the while loop writes anything to standard output). The FIFO has to be kept open by something on both the read end (which is being done by yuv4mpeg_to_v4l2) and on the write end (which I am doing with the redirection on the while loop). If mplayer is the only thing writing to the FIFO, the write end will close after mplayer finishes the conversion once and yuv4mpeg_to_v4l2 will see an EOF.
Hi everybody, first of all i am a new member in UNIX.com and this is my first post.
I am impressed with the amount of information a person can ever have in this forum, it is really great having something similiar; anyways let me tell you about the problem I am having, hope you will answer me.... (6 Replies)
Hi,
in my script I need to execute the following command:
query $id 456 432
but it waits for a RETURN character from keyboard and therefore, it fails. I tried something like:
query $id 456 432 << '\n'
but, i'ts clear it is not correct. Is there any way to do this?
Thxs. (0 Replies)
while running a user inter-active program
how can we get the commands from a
file instead of the user?
is there anyway to permanently redirect content
of a file to standard input? (6 Replies)
Hello,
I need to change user and run some commands by using a script.
lets say, I'm using
su - someuser << start
password required -----> how can I enter the password here
command 1
command 2
command 3
command 4
start
While trying to run this I got the following message:
"standard... (2 Replies)
Hello,
I need help with a bash script that I try to improve. I could not find answer so far, maybe because I'm not to familiar with the terminology so feel free to correct my language.
I have a script that looks like:
NODES="node_a node_b node_c"
for NODE in $NODES
do
... (4 Replies)
All,
I have a requirement to write a script where I check for Input redirection when the script was executed, based on which I handle my logic. Below is the example:
my.script
#! /bin/ksh
# Not sure how to frame the if condition below
if ; then
echo "Input Redirected from a file"
... (7 Replies)
Hello everyone,
My requirement is that within a script I need to construct the command line exactly that it was invoked with. For example :
sh a.sh arg1 arg2 arg3 < input.txt > output.txt
Now within a.sh, I construct a file which has these contents "
sh a.sh arg1 arg2 arg3 < input.txt >... (8 Replies)
Can someone please explain when input redirection is necessary?
For example, "cat filename" and "cat< filename" produce the same result. I was told that if I need to bunzip a file that I should type "bunzip2<filename.bz2." However, if I omit the "<" I still get the same result. Can someone... (4 Replies)
Hi,
when I try to redirect input and the command is described as a string within an array redirection does not work. why?
#!/bin/bash
dir=("tail < ./hello.txt")
tail < ./hello.txt #works
${dir} #does not work (2 Replies)
Discussion started by: heinzel
2 Replies
LEARN ABOUT PLAN9
pipe
PIPE(2) System Calls Manual PIPE(2)NAME
pipe - create an interprocess channel
SYNOPSIS
#include <u.h>
#include <libc.h>
int pipe(int fd[2])
DESCRIPTION
Pipe creates a buffered channel for interprocess I/O communication. Two file descriptors are returned in fd. Data written to fd[1] is
available for reading from fd[0] and data written to fd[0] is available for reading from fd[1].
After the pipe has been established, cooperating processes created by subsequent fork(2) calls may pass data through the pipe with read and
write calls. The bytes placed on a pipe by one write are contiguous even if many processes are writing. Write boundaries are preserved:
each read terminates when the read buffer is full or after reading the last byte of a write, whichever comes first.
The number of bytes available to a read(2) is reported in the Length field returned by fstat or dirfstat on a pipe (see stat(2)).
When all the data has been read from a pipe and the writer has closed the pipe or exited,read(2) will return 0 bytes. Writes to a pipe with no reader will generate a note sys: write on closed pipe.
SOURCE
/sys/src/libc/9syscall
SEE ALSO intro(2), read(2), pipe(3)DIAGNOSTICS
Sets errstr.
BUGS
If a read or a write of a pipe is interrupted, some unknown number of bytes may have been transferred.
When a read from a pipe returns 0 bytes, it usually means end of file but is indistinguishable from reading the result of an explicit write
of zero bytes.
PIPE(2)