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Full Discussion: while loops and variables under bash
Top Forums Shell Programming and Scripting while loops and variables under bash Post 302605025 by Corona688 on Tuesday 6th of March 2012 01:00:28 PM
Old 03-06-2012
It's not the different kinds of loops that are doing it -- it's the pipe that does it. By putting your while loop behind a pipe, you are executing it inside a subshell. Values get changed in the subshell, not the main one, and don't get copied back.

ksh organizes pipes in a different order than other Bourne shells. The innermost loop runs in the current shell while the outermost loop runs in the subshell. This is a KSH-only feature.

Depending on your goal, there are various ways to circumvent or just plain avoid this. This is a useless use of ls * for instance -- a situation where you might as well be using the * operator instead of the external ls utility.

Code:
for X in *
do
        let "u+=1"
done

The 'for' loop overcomes this by putting ls in backticks, which runs it first, and sets the value in a variable. But this is not recommended as it will be confused by filenames with spaces in them.
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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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