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Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!purdue!haven!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.bugs.4bsd,comp.unix.wizards
Subject: Re: csh problem involving nested ifs?
Keywords: csh, bug, nested if
Message-ID: <18476@mimsy.UUCP>
Date: 10 Jul 89 17:30:38 GMT
References: <685@wuphys.UUCP>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 49

In article <685@wuphys.UUCP> marty@wuphys.UUCP (Marty Olevitch) writes:
>It appears that csh does not correctly handle nested if-then-else
>statements.

This is false.  It does handle them, but it is finicky.

>Am I missing some bug in this script?

[all but the `if' lines deleted]

>if($v1 == 1) then
>	if($v2 == 1) then
>	if($v2 == 1) then

You must put a space after the `if', before the `('; and you must have
a space between the `)' and the `then' (which must be the last word on
the line, after stripping comments).

The reason is that the C shell's `skip to end of false construct' code
uses a completely different line parser than usual.  The `execute this line'
parser breaks lines at whitespace and at the characters ( ) & | and
perhaps a few others.  (&& and || are collected as a unit before causing
word breaks.)  The `skip to end of false if' routine winds up doing

	if (strcmp("if(", "if") == 0 && strcmp("then", "then") == 0)

in the particular cases given above.  Had you written

	if ($v2 == 1)then

it would have tried

	if (strcmp("if", "if") == 0 && strcmp(")then", "then") == 0)

and also failed.  Only

	if ($v2 == 1) then

and similar constructs pass its test.  (One such construct is

	if (this, {which is not &syntactically! correct, goes undetected then
		the c shell sucks
	endif

which counts as an `if-then' during false-if skipping, but causes an
error otherwise.)
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris