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From: dhesi%cirrusl@oliveb.ATC.olivetti.com (Rahul Dhesi)
Newsgroups: comp.mail.mh
Subject: Re: scan `pick ...`
Message-ID: <2944@cirrusl.UUCP>
Date: 12 Feb 91 22:43:10 GMT
References: <27B72875.12190@ics.uci.edu> <1501.666374307@note2.nsf.gov>
Sender: news@cirrusl.UUCP
Organization: Cirrus Logic Inc.
Lines: 39

>If the backquoted pick fails, it should return a failure
>code.  Some shells might still start up the command outside the
>backquotes while others do not.

When I use scan `pick ...` and the pick fails, the scan still
executes but reports no messages.  Here is what I see:

   % scan `pick last:20 -subject xyzzy`
   pick: no messages match specification
   scan: no messages match specification

Here is what my manual says for "pick":

     If pick is used in a back-quoted operation, such as

          scan `pick -from jones`

     and pick fails (e.g., no messages are  from  "jones"),  then
     the  shell  will still run the outer command (e.g., "scan").
     Since no messages were matched, pick produced no output, and
     the  argument  given  to  the  outer  command as a result of
     backquoting pick is empty.  In the case of MH programs,  the
     outer  command  now  acts  as if the default `msg' or `msgs'
     should be used (e.g., "all"  in  the  case  of  scan ).   To
     prevent  this unexpected behavior, if `-list' was given, and
     if its standard output is not a tty, then pick  outputs  the
     illegal  message  number  "0"  when it fails.  This lets the
     outer command fail gracefully as well.

Compile options for "pick" here are:

version: MH 6.6 #1[UCI] (ics) of Tue May 24 15:51:53 PDT 1988
options: [BSD42] [BERK] [TTYD] [MHE] [NETWORK] [BIND] [RPATHS]
         [SBACKUP='"#"'] [FOLDPROT='"0700"'] [MSGPROT='"0600"'] [MHRC]
         [MORE='"/user/bin/less"'] [OVERHEAD] [UCI] [UK] [NEED_FCNTL]
         [SENDMTS] [SMTP]
--
Rahul Dhesi <dhesi%cirrusl@oliveb.ATC.olivetti.com>
UUCP:  oliveb!cirrusl!dhesi