USER (was Re: exists or similar command to work like grep on file system files)

[Kenneth Brody]

On 2/13/2014 8:13 PM, Bruce Easton wrote:
> On 2/13/14 4:33 PM, Kenneth Brody wrote:
>> On 2/13/2014 3:52 PM, Bruce Easton wrote:
>>> On 2/13/14 3:30 PM, Kenneth Brody wrote:
>> [...]
>>>>         while read name
>>>>         do
>>>>             # The "real work" goes here.
>>>>         done
>>>>
>>> Ken, that technique for the script worked fine for me for one iteration
>>> from the processing table.  I don't know if it's that, in my example, I
>>> was repeating the call within @menu or something else, but when I tried
>>> repeating the "call" to the user program by start back at @menu (or even
>>> just below the user command), it would fail on the first repetition
>>> (using a while loop like you show here).
>>
>> What do you mean by "fail"?
> In the debugger, clerk would just hang with no error - as if waiting for
> more input.

Was there more input for it to get?

[...]
>> You could also do it "the right way" :-) with:
>>
>>      while read pattern
>>      do
>>          ls -1
>>          echo "**END**"
>>      done
>>
>> (You need some way for your processing to know that it reached the end
>> of the output list.  Hence the echo.)
>
> Yes that was the problem. The online manual page for this does have a
> warning at the bottom about looping till EOF, although not how to test
> EOF.  There is a line in the middle of that page that states "To test
> for an end-of-file or program termination, put the user program name on
> the condition line."  which is how I was trying to test for EOF in
> processing (and that didn't work without the close [userprogramname]).

But you haven't reached EOF, have you?  ("I'm done sending all of my output, 
and now I'm back at the 'read' line in the script" is *not* EOF.)

How to detect the end of a list whose length isn't known ahead of time is up 
to you.  Typically, it's done by sending one more string, containing a value 
which can't appear in the list itself, such as "END" after a list of 
numbers, or "/END/" in a list of filenames.  (Note that, technically, my 
example above could fail if you were to create a file named "**END**".)

[...]

-- 
Kenneth Brody