bin/162468: expr(1) false syntax errors

[Jilles Tjoelker]

The following reply was made to PR bin/162468; it has been noted by GNATS.

From: Jilles Tjoelker <jilles at stack.nl>
To: bug-followup at FreeBSD.org, egrosbein at rdtc.ru
Cc:  
Subject: Re: bin/162468: expr(1) false syntax errors
Date: Fri, 11 Nov 2011 16:44:55 +0100

 > [expr treats any string that looks like an operator as an operator,
 > for example, expr '>' : '.*' fails]
 
 The current behaviour of expr is allowed by POSIX (SUSv4, XCU 4
 Utilities, expr). If the application passes '>', this is not a string
 operand but an operator, even if that results in an invalid expression.
 This is also documented in the man page.
 
 It would be a valid extension to allow such expressions but it is not
 immediately clear how it would work. For example, should
   expr \( = \)
 compare two strings ("0") or return a single string ("=")? And should
   expr \( + \)
 return "+" or raise an error?
 
 The test utility is different in that POSIX specifies how a similar
 ambiguity shall be resolved (for a limited set of cases).
 
 Oh, and if you want to find a string length in a shell script, why don't
 you just use
   ${#VAR}
 (given that the string is in $VAR)? If you must use expr(1), do
   expr \( "x$VAR" : '.*' \) - 1
 as described in the man page.
 
 -- 
 Jilles Tjoelker