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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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LIBBASH(7)							  libbash Manual							LIBBASH(7)

NAME
libbash -- A bash shared libraries package. DESCRIPTION
libbash is a package that enables bash dynamic-like shared libraries. Actually its a tool for managing bash scripts whose functions you may want to load and use in scripts of your own. It contains a 'dynamic loader' for the shared libraries ( ldbash(1)), a configuration tool (ldbashconfig(8)), and some libraries. Using ldbash(1) you are able to load loadable bash libraries, such as getopts(1) and hashstash(1). A bash shared library that can be loaded using ldbash(1) must answer 4 requirments: 1. It must be installed in $LIBBASH_PREFIX/lib/bash (default is /usr/lib/bash). 2. It must contain a line that begins with '#EXPORT='. That line will contain (after the '=') a list of functions that the library exports. I.e. all the function that will be usable after loading that library will be listed in that line. 3. It must contain a line that begins with '#REQUIRE='. That line will contain (after the '=') a list of bash libraries that are required for our library. I.e. every bash library that is in use in our bash library must be listed there. 4. The library must be listed (For more information, see ldbashconfig(8)). Basic guidelines for writing library of your own: 1. Be aware, that your library will be actually sourced. So, basically, it should contain (i.e define) only functions. 2. Try to declare all variables intended for internal use as local. 3. Global variables and functions that are intended for internal use (i.e are not defined in '#EXPORT=') should begin with: __<library_name>_ For example, internal function myfoosort of hashstash library should be named as __hashstash_myfoosort This helps to avoid conflicts in global name space when using libraries that come from different vendors. 4. See html manual for full version of this guide. AUTHORS
Hai Zaar <haizaar@haizaar.com> Gil Ran <ril@ran4.net> SEE ALSO
ldbash(1), ldbashconfig(8), getopts(1), hashstash(1) colors(1) messages(1) urlcoding(1) locks(1) Linux Epoch Linux
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