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Full Discussion: Incrementing Variable resets outside of while loop
Homework and Emergencies Homework & Coursework Questions Incrementing Variable resets outside of while loop Post 302394500 by Corona688 on Thursday 11th of February 2010 03:13:16 PM
Old 02-11-2010
It's because of the pipe.

Code:
#!/bin/sh
      count=0
      who | cut -f1 -d" " > temp
      cat temp
      rm temp
      echo "Enter the user whose processes you would like to see"
      read username
      #ps -l -u $username 2>/dev/null
      ps -acefl | while read line
      do
        carl=`echo $line | cut -f3 -d" "`        
        if [ "$carl" = "$username" ]; then
          
          #count=`expr count=$count + 1`         
          (( count= $count + 1 ))

#count is displayed correctly
          echo $count 

          echo $line
        fi
      done
      echo $count 

      #at this point "count = 0"

      if [ $count == 0 ]; then
        echo "Either that user does not exist or is not running"
      fi

When you put a code block behind a pipe, the entire block executes in a subshell. The subshell inherits a copy of the shell's current variables but cannot communicate them back(much like how processes inherit environment variables). So the loop runs fine but the number you want was never in the parent shell.

You could either accomplish the loop without a pipe (perhaps by saving the output of ps to a temporary file), or have the loop output values to stdout to be read further down the pipe chain.


P.S.: You could replace
Code:
      who | cut -f1 -d" " > temp
      cat temp
      rm temp

with
Code:
      who | cut -f1 -d" "

There seems to be no point to saving it to a temp file when all you want it to do is print to the console anyway.
Last edited by Corona688; 02-11-2010 at 04:29 PM..
 

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LEARN ABOUT SUNOS

continue

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)
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