Path: utzoo!attcan!uunet!cs.utexas.edu!rutgers!bpa!dsinc!lgnp1!rbarrell
From: rbarrell@lgnp1.LS.COM (Robert Barrell)
Newsgroups: comp.unix.questions
Subject: How to tell if you're in a pipe...
Keywords: pipe tty(1) sh(1) isatty(4)
Message-ID: <1798@lgnp1.LS.COM>
Date: 22 Jun 89 11:55:53 GMT
Organization: Lagniappe Systems [Norristown PA]
Lines: 28


     [The machine through which I usually access the newsgroups had a bit of
a burp, so please forgive me if I'm repeating an answer, here.]  
  
     I don't know if it was ever answered, or not, but someone had asked about
how to determine if the program they were running was being used directly, or
in a pipe.  In glancing through the manuals, I happened to notice the isatty()
C call, and what it does, which prompted me to examine the "tty" shell command.
In doing so, I found that "tty" returns a 0 if standard-input is a terminal,
and returns a 1 if it isn't.  Also, with the "-s" option, "tty" can be made
silent, so the exit code may be used without having to redirect the output of
"tty" to /dev/null.  Thus, the following script will tell you if it is being
run in a pipe or not:  

     if [ `tty -s;echo $?` = 0 ]
     then
         echo "terminal"
     else
         echo "pipe"
     fi

     I hope this isn't to late (or already redundant) to be of use to the
person who originally asked the question.
------------------------------------------------------------------------------
     Robert Barrell
     "Hodgepodge" - Sysop of Milo's Meadow - A Citadel/UX BBS
     215-323-0497 - 300/1200/2400 - 24hrs. - login as "bbs"
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