Signal trapped during read resumes sleeping Post: 302977314

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Top Forums Shell Programming and Scripting Signal trapped during read resumes sleeping Post 302977314 by Corona688 on Friday 15th of July 2016 05:26:53 PM

07-15-2016

Registered User

I don't think the "resethand" issue is related. Your shell has no issue receiving the interrupt, and does exactly what you told it to do -- wait for input. What needs to be told that something is happening is read. How can you do that? Close whatever it's reading from. Killing tail would do it, for example. Or using a named pipe and forcing it to close.

Code:

#!/bin/ksh

# On ctrl-C, close the read-end of the named pipe.
trap 'echo "Closing FIFO" ; exec 5<&-' INT

mkfifo $$ # Create a named pipe file in the current directory

# Open one end of pipe in background, read from log file,
# write into pipe.
# This will hang until we open the other end,
# so we have to put it in the background.
(exec tail -f /var/log/logfile > $$) &

exec 5<$$ # Open the other end in our shell, into file descriptor 5.
rm /tmp/$$ # Clean up mess

# Read from file descriptor 5 until something forces it to close,
# whether it be tail quitting, the pipe closing, or the apocalypse
while read LINE
do
        echo "$LINE"
done <&5

wait # wait for tail to quit.  Closing our end of the pipe ought to force it to quit (it will get SIGPIPE)

echo "Normal exit"

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LEARN ABOUT SUNOS

echo

echo(1B)					     SunOS/BSD Compatibility Package Commands						  echo(1B)

NAME

       echo - echo arguments to standard output

SYNOPSIS

       /usr/ucb/echo [-n] [argument]

DESCRIPTION

       echo writes its arguments, separated by BLANKs and terminated by a NEWLINE, to the standard output.

       echo  is useful for producing diagnostics in command files and for sending known data into a pipe, and for displaying the contents of envi-
       ronment variables.

       For example, you can use echo to determine how many subdirectories below the root directory (/) is your current directory, as follows:

	 o  echo your current-working-directory's full pathname

	 o  pipe the output through tr to translate the path's embedded slash-characters into space-characters

	 o  pipe that output through wc -w for a count of the names in your path.

	      example% /usr/bin/echo "echo $PWD | tr '/' ' ' | wc -w"

       See tr(1) and wc(1) for their functionality.

       The shells csh(1), ksh(1), and sh(1), each have an echo built-in command, which, by default, will have precedence, and will be  invoked	if
       the  user  calls  echo without a full pathname. /usr/ucb/echo and csh's echo() have an -n option, but do not understand back-slashed escape
       characters. sh's echo(), ksh's echo(), and /usr/bin/echo, on the other hand, understand the  black-slashed  escape  characters,	and  ksh's
       echo() also understands a as the audible bell character; however, these commands do not have an -n option.

OPTIONS

       -n	Do not add the NEWLINE to the output.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWscpu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       csh(1), echo(1), ksh(1), sh(1), tr(1),  wc(1), attributes(5)

NOTES

       The -n option is a transition aid for BSD applications, and may not be supported in future  releases.

SunOS 5.10							    3 Aug 1994								  echo(1B)