Help with trap and signals Post: 302843648

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Top Forums Shell Programming and Scripting Help with trap and signals Post 302843648 by Basherrr on Wednesday 14th of August 2013 09:46:14 AM

08-14-2013

Registered User

Help with trap and signals

I am having issues with trap not working inside a script. I am currently trying this on a Knoppix system V 5.1. What I would like to happen is when I press control c, a message gets echoed and the script is ended. For example:

Code:

#! /bin/bash
 
 
trap "echo CTRL c was pressed ; break" SIGINT SIGTERM 
 
 
while :
do
      :
done

When I press CTRL c in the above example, A message gets echoed and the loop is ended and that's the end of the script. Pretty straight forward; however, when I put a "sleep 5" in the while loop and run the script, then press CTRL c, no message is echoed to the screen. Also the loop does not exit. Ex:

Code:

#! /bin/bash
 
 
   trap "echo CTRL c was pressed ; break" SIGINT SIGTERM
 
   sleep 5
 
 
 
  while :
  do
        echo in loop now
        sleep 5
 
 done

***NOTE*** If you try this above code you will create an infinite loop and CTRL c. will no longer work.

Once I add in the sleep command in the loop, CTRL C no longer prints a message and no longer breaks out of the loop. Does anyone know how to get around this and why the trap stops working when a sleep command is used in the loop.

I was thinking it had something to do with the trap statements having to wait till the sleep 5 to finish running and then the trap handler gets executed, but the trap is never getting ran. I am guessing it has to do with something else. Thanks in advance for your help.

Basherrr

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LEARN ABOUT V7

break

break(1)                                                           User Commands                                                          break(1)

NAME

       break, continue - shell built-in functions to escape from or advance within a controlling while, for, foreach, or until  loop

SYNOPSIS

   sh
       break [n]

       continue [n]

   csh
       break

       continue

   ksh
       *break [n]

       *continue [n]

DESCRIPTION

   sh
       The break utility exits from the enclosing for or while loop, if any. If n is specified, break n levels.

       The continue utility resumes the next iteration of the enclosing for or while loop. If n is specified, resume at the n-th enclosing loop.

   csh
       The  break  utility  resumes  execution after the end of the nearest enclosing foreach or while loop. The remaining commands on the current
       line are executed. This allows multilevel breaks to be written as a list of break commands, all on one line.

       The continue utility continues execution of the next iteration of the nearest enclosing while or foreach loop.

   ksh
       The break utility exits from the enclosed for, while, until, or select loop, if any. If n is specified,  then  break  n  levels.  If  n  is
       greater than the number of enclosing loops, the outermost enclosing loop shall be exited.

       The  continue utility resumes the next iteration of the enclosed for, while, until, or select loop. If n is specified then resume at the n-
       th enclosed loop. If n is greater than the number of enclosing loops, the outermost enclosing loop shall be used.

       On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways:

       1.  Variable assignment lists preceding the command remain in effect when the command completes.

       2.  I/O redirections are processed after variable assignments.

       3.  Errors cause a script that contains them to abort.

       4.  Words that follow a command preceded by ** that are in the format of a variable assignment are expanded with the same rules as a  vari-
           able  assignment.  This means that tilde substitution is performed after the = sign, and also that word splitting and file name genera-
           tion are not performed.

ATTRIBUTES

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

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE         |      ATTRIBUTE VALUE        |
       +-----------------------------+-----------------------------+
       |Availability                 |SUNWcsu                      |
       +-----------------------------+-----------------------------+

SEE ALSO

       csh(1), exit(1), ksh(1), sh( 1), attributes(5)

SunOS 5.10                                                          17 Jul 2002                                                           break(1)