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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 DEBIAN

getbddvarindex

GETBDDVARINDEX(3)						   BDD FUNCTIONS						 GETBDDVARINDEX(3)

NAME

       getbddvarindex - converts a variable number in a bdd index.

ORIGIN

       This  software  belongs	to  the  ALLIANCE CAD SYSTEM developed by the ASIM team at LIP6 laboratory of Universite Pierre et Marie CURIE, in
       Paris, France.

       Web : http://asim.lip6.fr/recherche/alliance/
       E-mail : alliance-users@asim.lip6.fr

SYNOPSYS

       #include "bdd101.h"
       bddindex getbddvarindex( BddSystem, Variable )
	 bddsystem *BddSystem;
	 bddvar     Variable;

PARAMETERS

       BddSystem	   The bdd system.

       Variable 	   The variable number to convert.

DESCRIPTION

       getbddvarindex converts the variable number Variable to a bdd index, in the bdd system BddSystem.  If a null pointer is given, the  default
       bdd system is used.  The function uses simply the translation table BddSystem->VAR_TO_INDEX.

RETURN VALUE

       getbddvarindex returns the bdd index of Variable.

ERRORS

       "variable xxx out of range, error !"
	      The Variable parameter must be less or equal to the BddSystem->NUMBER_VAR field.

EXAMPLE

       #include "bdd101.h"
	  bddsystem  *BddSystem;
	  bddnode    *BddNode;
	  BddSystem  = createbddsystem( 100, 1000, 100, 50000 );
	  BddNode = addbddvar( (bddsystem *)0, 0 );
	  /* displays 2 */
	  printf( "%d", getbddvarindex( (bddsystem *)0, 0 ) );
	  destroybddsystem( (bddsystem *)0 );

SEE ALSO

       bdd(1)

BUG REPORT

       This tool is under development at the ASIM department of the LIP6 laboratory.
       We need your feedback to improve documentation and tools.

ASIM
/LIP6							  October 1, 1997						 GETBDDVARINDEX(3)
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