Help Understanding While Loop

Drew Tomlinson drew at mykitchentable.net
Sat Oct 15 15:59:34 PDT 2005


On 10/14/2005 3:24 PM David Kirchner wrote:

>On 10/14/05, Drew Tomlinson <drew at mykitchentable.net> wrote:
>  
>
>>OK, I've been working on an sh script and I'm almost there.  In the
>>script, I created a 'while read' loop that is doing what I want.  Now I
>>want to keep track of how many times the loop executes.  Thus I included
>>this line between the 'while read' and 'done' statements:
>>
>>count = $(( count + 1 ))
>>
>>I've tested this by adding an 'echo $count' statement in the loop and it
>>increments by one each time the loop runs.  However when I attempt to
>>call $count in an 'echo' statement after the 'done', the variable is
>>null.  Thus I assume that $count is only local to the loop and I have to
>>export it to make it available outside the loop?  What must I do?
>>    
>>
>
>Oh yeah, that's another side effect of using the while read method.
>Because it's "| while read" it's starting a subshell, so any variables
>are only going to exist there. You'd need to have some sort of 'echo'
>within the while read, and then | wc -l at the end of the while loop,
>or something along those lines.
>
>The IFS method someone else mentioned, in regards to 'for' loops,
>would probably be better all around. So you'd want:
>
>OLDIFS=$IFS
># Note this is a single quote, return, single quote, no spaces
>IFS='
>'
>
>for i in `find etc`
>do
>done
>
>IFS=$OLDIFS
>  
>

OK, I've tried this and it does fix the "count" problem.  However it 
messes up another part of the script and I'm trying understand why.  I 
tried to make this script dynamic in that all I would need to do is edit 
variables set at the top and then not have to worry about all 
occurrences in the script.  Thus I set the following variables:

remote_pictures_dir="/multimedia/Pictures"
local_pictures_dir="/tv/pictures"
find_args="-iname '*.jpg' -or -iname '*.gif'"

Then I called the 'find' command as follows:

for original in $(/usr/bin/find $remote_pictures_dir $find_args -print)

But when I run my script, I get "/usr/bin/find: invalid predicate 
`-iname '*.jpg' -or -iname '*.gif''".  However if I don't try and use 
$find_args and type the arguments in specifically, the script runs 
fine.  I tried various combinations of quoting and escaping those quotes 
but can't come up with a combination that works.

What is going on?  And is there some way to set verbosity so I can see 
how the shell is expanding the variables?

Thanks much,

Drew

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