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Top Forums Shell Programming and Scripting How to send data to previous program (pipe)? Post 303012639 by JackK on Wednesday 7th of February 2018 08:26:21 AM
Old 02-07-2018
Quote:
Originally Posted by Peasant
You can achieve this using shell coprocesses

There are examples on this forum and online.
I found one done example by doing sqlplus cooprocess ksh search in google.

Regards
Peasant.
I didn't know about coprocesses before. In my case, I think, writing a parser with coprocesses is not needed and too complicated (for such a small requirement).

Is it possible to do a redirection to a process by it's PID? For example:
Code:
$ echo "something" > PID#

Quote:
Originally Posted by Don Cragun
Send email to yourself, send a message to a message queue, write to a regular file, write to a FIFO file, send a signal, write some text into a shared memory segment... There are hundreds of ways to do this.
May you provide an example, please? It would be good to send a signal from cmd2 to cmd1, but how may I tell cmd1 to interpret the signal I a proper way (changing sqlprompt)?

---------- Post updated at 01:57 PM ---------- Previous update was at 01:46 PM ----------

I found something. When I have sqlplus running and in another session I do:
Code:
# echo "TEst;" > /proc/<PIDofSQLPLUS>/fd/0

then in sqlplus I receive:
Quote:
myuser@mydb SQL> TEst;
But the message is not interpreted at all (is only printed) by sqlplus, unfortunately.

---------- Post updated at 04:26 PM ---------- Previous update was at 01:57 PM ----------

According to my last update I found this (linux - sending command to process using /proc - Stack Overflow):
Quote:
You can't do that. /proc/fd/0 is (usually) not a pipe which you can write to and give the process input.
What you need to do, is invoke the process with its stdin coming from something that IS a pipe (or socket etc) so that you can write stuff into it.
A named pipe MAY work here (see mknod(1) or mkfifo(3) ).
 

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fflush(3C)						   Standard C Library Functions 						fflush(3C)

NAME
fflush - flush a stream SYNOPSIS
#include <stdio.h> int fflush(FILE *stream); DESCRIPTION
If stream points to an output stream or an update stream in which the most recent operation was not input, fflush() causes any unwritten data for that stream to be written to the file, and the st_ctime and st_mtime fields of the underlying file are marked for update. If stream points to an input stream or an update stream into which the most recent operation was input, that stream is flushed if it is seekable and is not already at end-of-file. Flushing an input stream discards any buffered input and adjusts the file pointer such that the next input operation accesses the byte after the last one read. A stream is seekable if the underlying file is not a pipe, FIFO, socket, or TTY device. If stream is a null pointer, fflush() performs this flushing action on all streams for which the behavior is defined above. An input stream, seekable or non-seekable, can be flushed by explicitly calling fflush() with a non-null argument specifying that stream. RETURN VALUES
Upon successful completion, fflush() returns 0. Otherwise, it returns EOF and sets errno to indicate the error. ERRORS
The fflush() function will fail if: EAGAIN The O_NONBLOCK flag is set for the file descriptor underlying stream and the process would be delayed in the write opera- tion. EBADF The file descriptor underlying stream is not valid. EFBIG An attempt was made to write a file that exceeds the maximum file size or the process's file size limit; or the file is a regular file and an attempt was made to write at or beyond the offset maximum associated with the corresponding stream. EINTR The fflush() function was interrupted by a signal. EIO The process is a member of a background process group attempting to write to its controlling terminal, TOSTOP is set, the process is neither ignoring nor blocking SIGTTOU, and the process group of the process is orphaned. ENOSPC There was no free space remaining on the device containing the file. EPIPE An attempt is made to write to a pipe or FIFO that is not open for reading by any process. A SIGPIPE signal will also be sent to the calling process. The fflush() function may fail if: ENXIO A request was made of a non-existent device, or the request was beyond the limits of the device. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ SEE ALSO
getrlimit(2), ulimit(2), attributes(5), standards(5) SunOS 5.10 1 Nov 2003 fflush(3C)
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