Bug 5338 - tcsh && is not short circuiting
tcsh && is not short circuiting
Status: CLOSED NOTABUG
Product: Red Hat Linux
Classification: Retired
Component: tcsh (Show other bugs)
6.0
i386 Linux
medium Severity medium
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Assigned To: Nalin Dahyabhai
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Depends On:
Blocks:
  Show dependency treegraph
 
Reported: 1999-09-23 16:26 EDT by jfoster
Modified: 2008-05-01 11:37 EDT (History)
1 user (show)

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Doc Type: Bug Fix
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Last Closed: 2002-03-25 00:38:22 EST
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Description jfoster 1999-09-23 16:26:07 EDT
Running the following script yields the error "X11:
Undefined variable," whereas it should exit normally.

-----------------------------------------------------
#!/bin/tcsh

unsetenv X11
if ($?X11 && ($X11 == "huh?")) then
   echo "a"
endif
echo "b"
-----------------------------------------------------
Comment 1 Jeff Johnson 2000-01-10 15:48:59 EST
This bug is still present in tcsh-6.09-1.
Comment 2 Göran Uddeborg 2001-07-17 17:30:25 EDT
This is not a bug, is it?  Variable expansion takes place in one step for a
complete line, before any evaluation of the expression or execution of command. 
As far as I'm aware, it has always been necessary to do

if ($?X11) then
   if ($X11 == "huh?") then
      echo "a"
   endif
endif

to achieve the desired effect.  Both in tcsh and in the original csh.
Comment 3 jfoster 2001-07-17 18:40:06 EDT
OK, it's a feature then.
Comment 4 Ben Liblit 2001-07-17 20:12:15 EDT
The reported behavior is surprising but correct.  Read "Csh Programming
Considered Harmful", section 6 (Expression Evaluation). 
<http://www.perl.com/pub/a/language/versus/csh.html>

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