Re: Variables from while/read loops not seen outside of loop

[Chet Ramey]

peter.kielbasiewicz@philips.com wrote:

> I have various HPUX shell scripts that use the technique below and I do 
> need to port them to Linux.
> In HPUX's Posix shell it  is common practice to parse files like:
>
> cat $file | while read line
>                   do
>                            ... parse lines and assign results to 
> variables...
>                   done
>                   ... print formatted output of resulting variables...
>
> Unfortunately this does not work at all in bash and I found the reason 
> under FAQ E4.
> All variables set inside the while/read loop are not passed to the parent 
> shell and thus are unset when I want to print my formatted result
>
> There are two questions here:
>    1. How does HPUX manage to handle the problem 

ksh is internally structured to run the last element of a pipeline in
the current shell, and HPUX's `posix shell' is based on ksh.

>    2. How can I write a solution in bash which gives the desired result

There are a number of suggestions in the FAQ.  The easiest is to change

        cat $file | while ... ; do .... ; done

to

        while ... ; do ... ; done < $file

which does not create a subshell.

Chet
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
( ``Discere est Dolere'' -- chet )
                                                Live...Laugh...Love
Chet Ramey, ITS, CWRU    chet@po.cwru.edu 
http://tiswww.tis.cwru.edu/~chet/