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Full Discussion: Help in co-process issue
Top Forums Shell Programming and Scripting Help in co-process issue Post 302141114 by bakunin on Wednesday 17th of October 2007 06:56:45 PM
Old 10-17-2007
I really hate to say it, but:

@porter: please do not answer to threads where you have obviously not the slightest idea of what is being spoken about.

Coprocesses are a device in the Korn Shell with which a background process can be started but (unlike usual background processes) communication between the father- and the child-process is being maintained.

By default coprocesses communicate via I/O-channel 4 and 5 with the father process. That means if a coprocess sends something to its <stdout> it can be in the father process by reading from channel 4 and writing to channel 5 in the father process appear in <stdin> of the child process.

The reason why this is valuable for scripts using ftp is because ftp is designed as an interactive program and not very well suited for batch operation. Hence one can start the ftp-process as coprocess and process the output and provide the input within the father process, quasi-simulating an interactive ftp-session.

Get yourself a good Korn Shell book (I'd strongly recommend Barry Rosenbergs "Hands-on Kornshell93 programming", very informative AND funny to read) to find about about the coprocess facility in ksh.

bakunin
 

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PIDOF(8)						Linux System Administrator's Manual						  PIDOF(8)

NAME
pidof -- find the process ID of a running program. SYNOPSIS
pidof [-s] [-c] [-n] [-x] [-o omitpid[,omitpid..]] [-o omitpid[,omitpid..]..] program [program..] DESCRIPTION
Pidof finds the process id's (pids) of the named programs. It prints those id's on the standard output. This program is on some systems used in run-level change scripts, especially when the system has a System-V like rc structure. In that case these scripts are located in /etc/rc?.d, where ? is the runlevel. If the system has a start-stop-daemon (8) program that should be used instead. OPTIONS
-s Single shot - this instructs the program to only return one pid. -c Only return process ids that are running with the same root directory. This option is ignored for non-root users, as they will be unable to check the current root directory of processes they do not own. -n Avoid stat(2) system function call on all binaries which are located on network based file systems like NFS. Instead of using this option the the variable PIDOF_NETFS may be set and exported. -x Scripts too - this causes the program to also return process id's of shells running the named scripts. -o omitpid Tells pidof to omit processes with that process id. The special pid %PPID can be used to name the parent process of the pidof pro- gram, in other words the calling shell or shell script. EXIT STATUS
0 At least one program was found with the requested name. 1 No program was found with the requested name. NOTES
pidof is actually the same program as killall5; the program behaves according to the name under which it is called. When pidof is invoked with a full pathname to the program it should find the pid of, it is reasonably safe. Otherwise it is possible that it returns pids of running programs that happen to have the same name as the program you're after but are actually other programs. Note that that the executable name of running processes is calculated with readlink(2), so symbolic links to executables will also match. SEE ALSO
shutdown(8), init(8), halt(8), reboot(8), killall5(8) AUTHOR
Miquel van Smoorenburg, miquels@cistron.nl 01 Sep 1998 PIDOF(8)
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