Detecting Pipe Using Bourne Shell

[Lloyd Kremer]

In article: <18992 at adm.BRL.MIL> ifenn%ee.surrey.ac.uk at nss.cs.ucl.ac.uk (Ian Fenn) writes:

>If I enter the program with 
>no arguments:
>I display a main menu which offers options to change entries,
>delete entries, etc, etc. If I enter the program with arguments
>Then it searches through the database (using grep) for the arguments
>using:

>if test $# -ne 
>then	.....search for arguments in database.....
>	.....then exit
>fi
>....rest of program (i.e. Main Menu).

>The only problem with this is that I cannot pipe the output from another 
>program into it because it drops into the main menu and out again!
>% cat datafile | phone 


You are trying to interpret "no arguments" as two entirely different directives:
a) present menu and exit
and
b) read stdin instead of argument list for search targets

You must devise a way of differentiating between these meanings.  Many UNIX(tm)
programs treat an argument of  -  as meaning 'read stdin instead of files'.

How about something like this:

	#!/bin/sh
	# phone lookup utility

	if [ $# = 0 ]
	then
		present menu
	elif [ $1 = - ]
	then
		while read $i
		do
			grep "$i" database
		done
	else
		for i in $*
		do
			grep "$i" database
		done
	fi
	exit 0

Or, to be a bit more elegant:

	#!/bin/sh
	# phone lookup utility

	if [ $# = 0 ]
	then
		present menu
	else
		if [ $1 = - ]
		then
			set `while read i;do echo "$i";done`
		fi
		for i in $*
		do
			grep "$i" database
		done
	fi
	exit 0


Either of these should allow
	some_program | phone -
to work properly.

					Hope this helps,

					Lloyd Kremer
					{uunet,sun,...}!xanth!kremer