Grab exactly one byte from a FIFO, at random intervals Post: 302747901

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Top Forums Shell Programming and Scripting Grab exactly one byte from a FIFO, at random intervals Post 302747901 by vomv1988 on Sunday 23rd of December 2012 04:34:44 PM

12-23-2012

Registered User

I'm currently using bash in a mac, but I was testing the code from the original post also in GNU/Linux, in bash too.

I see how several unterminated instances of the 'listen' section would cause the behavior. I used ps to check, and killed all undesired instances of the listen section, but that didn't seem to solve it. So I split the script into two scripts:

listen.sh

Code:

#!/bin/bash

# Listen

	IFS=
	tail -f INPUT | while read -n 1 CHAR ; do
		printf "${CHAR}" > FIFO
#		sleep 0.2
	done

EDIT: The behavior only happens without the sleep delay. But I would like to have a working script that does not require the sleep delay.

prompt.sh

Code:

#!/bin/bash

PROMPT=n
while test ${PROMPT} != 'q' ; do
	printf 'y: print next byte\nn: don'"'"'t print next byte\nq: quit\n'
	read -n 1 PROMPT
	printf '\n'
	if test "${PROMPT}" = 'y' ; then

# Grab 1 byte

		BYTE=`cat FIFO`
		printf 'The input byte is:\n'
		printf "${BYTE}" | xxd -cols 1
	fi
done

So, on one terminal, I run ./listen.sh, and I leave it there, on a second one, I run ./prompt.sh, and leave it there also, and finally, on a third terminal, I run "printf 'Hello, world!' > INPUT".

I go back to the second terminal, and type 'y', and get the same undesired behavior. This time, I made sure there were no undesired unterminated instances of the listen section. bipinajith: Are you using the exact same code from my original post, or did you add any changes to yours?

vomv1988

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setusershell

getusershell(3C)					   Standard C Library Functions 					  getusershell(3C)

NAME

       getusershell, setusershell, endusershell - get legal user shells

SYNOPSIS

       #include <unistd.h>

       char *getusershell(void);

       void setusershell(void);

       void endusershell(void);

DESCRIPTION

       The  getusershell()  function  returns  a  pointer  to  a  legal  user  shell  as defined by the system manager in the file /etc/shells. If
       /etc/shells does not exist, the following locations of the standard system shells are used in its place:

       /bin/bash		  /bin/csh
       /bin/jsh 		  /bin/ksh
       /bin/pfcsh		  /bin/pfksh
       /bin/pfsh		  /bin/sh
       /bin/tcsh		  /bin/zsh
       /sbin/jsh		  /sbin/pfsh
       /sbin/sh 		  /usr/bin/bash
       /usr/bin/csh		  /usr/bin/jsh
       /usr/bin/ksh		  /usr/bin/pfcsh
       /usr/bin/pfksh		  /usr/bin/pfsh
       /usr/bin/sh		  /usr/bin/tcsh
       /usr/bin/zsh		  /usr/xpg4/bin/sh

       The getusershell() function opens the file /etc/shells, if it exists, and returns the next entry in the list of shells.

       The setusershell() function rewinds the file or the list.

       The endusershell() function closes the file, frees any memory used by getusershell() and setusershell(), and rewinds the file /etc/shells.

RETURN VALUES

       The getusershell() function returns a null pointer on EOF.

BUGS

       All information is contained in memory that may be freed with a call to endusershell(), so it must be copied if it is to be saved.

SunOS 5.10							    30 Aug 2004 						  getusershell(3C)