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Full Discussion: how to get the variable in while loop outside of it?
Top Forums Shell Programming and Scripting how to get the variable in while loop outside of it? Post 302571233 by agama on Sunday 6th of November 2011 11:45:10 PM
Old 11-07-2011
This is an issue caused with the way bash implements pipes. When piping input to a while, I believe that bash executed the while in a child processes which causes any changes to variables inside of the while to be lost.


This is one reason I prefer kshell over bash. If you have a modern kshell, I suggest you use it. If not then try writing your output to a temp file and reading it into the while.
Code:
x=0
ls | while read f
do
    x=$(( $x + 1 ))
    printf "in loop: $x\n"
done
printf "after loop: $x\n"

 ls >/tmp/ls
x=0

 while read f
do
    x=$(( $x + 1 ))
    printf "in loop: $x\n"
done </tmp/ls
printf "after second loop: $x\n"

Try this in both shells to see the difference. Ksh gets the answer right after the loop both times.
Last edited by agama; 11-07-2011 at 12:45 AM.. Reason: typo
 

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LEARN ABOUT REDHAT

open

OPEN(1) 							     Linux 1.x								   OPEN(1)

NAME

       open - start a program on a new virtual terminal (VT).

SYNOPSIS

       open [-c vtnumber] [-s] [-u] [-l] [-v] [--] command command_options

DESCRIPTION

       open will find the first available VT, and run on it the given command with the given command options, standard input, output and error are
       directed to that terminal. The current search path ($PATH) is used to find the requested command. If no command is specified then the envi-
       ronment variable $SHELL is used.

   OPTIONS
       -c vtnumber
	      Use the given VT number and not the first available. Note you must have write access to the supplied VT for this to work.

       -s     Switch to the new VT when starting the command. The VT of the new command will be made the new current VT.

       -u     Figure out the owner of the current VT, and run login as that user.  Suitable to be called by init. Shouldn't be used with -c or -l.

       -l     Make the command a login shell. A - is prepended to the name of the command to be executed.

       -v     Be a bit more verbose.

       -w     wait for command to complete. If -w and -s are used together then open will switch back to the controlling terminal when the command
	      completes.

       --     end of options to open.

NOTE

       If open is compiled with a POSIX (Gnu) getopt() and you wish to set options to the command to be run, then  you	must  supply  the  end	of
       options -- flag before the command.

EXAMPLES

       open can be used to start a shell on the next free VT, by using the command:

       open bash

       To start the shell as a login shell, use:

       open -l bash

       To get a long listing you must supply the -- separator:

       open -- ls -l

SEE ALSO

       login(1), doshell(8), switchto(1).

AUTHOR

       Jon Tombs <jon@gtex02.us.es or jon@robots.ox.ac.uk>
       -w idea from "sam".

19 Jul 1996							       V1.4								   OPEN(1)
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