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Full Discussion: how to exit a while true loop
Top Forums Shell Programming and Scripting how to exit a while true loop Post 302133757 by Perderabo on Saturday 25th of August 2007 08:25:43 AM
Old 08-25-2007
Code:
#! /usr/local/bin/bash
count=0
while : ; do
        echo count = $count
        ((count=count+1))
        read -t 10 && break
done
echo exited while loop
exit 0

This uses the -t option to the read command in bash. The "count" is just to have something that changes to display with each iteration. If the user presses return within 10 seconds, the read succeeds, otherwise it fails. (If it succeeds, we just discard the data that was read since no variable is used with the read.) -t works with bash, but most versions of ksh do not have it.
 

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LEARN ABOUT CENTOS

true

TRUE(1P)						     POSIX Programmer's Manual							  TRUE(1P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       true - return true value

SYNOPSIS

       true

DESCRIPTION

       The true utility shall return with exit code zero.

OPTIONS

       None.

OPERANDS

       None.

STDIN

       Not used.

INPUT FILES

       None.

ENVIRONMENT VARIABLES

       None.

ASYNCHRONOUS EVENTS

       Default.

STDOUT

       Not used.

STDERR

       Not used.

OUTPUT FILES

       None.

EXTENDED DESCRIPTION

       None.

EXIT STATUS

       Zero.

CONSEQUENCES OF ERRORS

       None.

       The following sections are informative.

APPLICATION USAGE

       This utility is typically used in shell scripts, as shown in the EXAMPLES section. The special built-in utility : is sometimes  more  effi-
       cient than true.

EXAMPLES

       This command is executed forever:

	      while true
	      do
		  command
	      done

RATIONALE

       The  true utility has been retained in this volume of IEEE Std 1003.1-2001, even though the shell special built-in : provides similar func-
       tionality, because true is widely used in historical scripts and is less cryptic to novice script readers.

FUTURE DIRECTIONS

       None.

SEE ALSO

       false, Shell Commands

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and  the  original  IEEE
       and  The  Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained
       online at http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003								  TRUE(1P)
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