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Full Discussion: Correct bash substitution
Top Forums Shell Programming and Scripting Correct bash substitution Post 302449109 by agama on Saturday 28th of August 2010 01:15:29 PM
Old 08-28-2010
This, in my opinion, is one of the serious shortcomings of bash. When piping the output of a command to a while loop, the contents of the while are executed in a forked process and thus variables that are local to the script, and should logically be updated as a part of the loop, are not.

I'd run your script using ksh (#!/usr/bin/env ksh) provided it is installed on your host.

Small example to illustrate:
Code:
# count lines in output from ps command
var=1
ps -ef | while read x
do
        var=$(( $var + 1 ))
done
echo $var

Running the script (t22) with bash vs ksh:
Code:
$ ksh t22
126
$ bash t22
1

Ksh does it right, the variable var is updated in the while as expected. Ksh also supports the ${!name} construct you are looking for.

The kshell man page:
http://www2.research.att.com/sw/down.../man1/ksh.html
Last edited by agama; 08-28-2010 at 02:17 PM.. Reason: changed wording to make more clear.
This User Gave Thanks to agama For This Post:
teresaejunior
 

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LEARN ABOUT XFREE86

times

times(1)                                                           User Commands                                                          times(1)

NAME

       times - shell built-in function to report time usages of the current shell

SYNOPSIS

   sh
       times

   ksh
       times

DESCRIPTION

   sh
       Print the accumulated user and system times for processes run from the shell.

   ksh
       Print the accumulated user and system times for the shell and for processes run from the shell.

       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,  following 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 word splitting and file name generation  are  not
           performed.

ATTRIBUTES

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

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

SEE ALSO

       ksh(1), sh(1), time(1), attributes(5)

SunOS 5.10                                                          15 Apr 1994                                                           times(1)
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