Date: Thu, 28 Jun 2001 21:42:20 -0700 From: Dave Tweten <tweten@nas.nasa.gov> To: Pete Fritchman <petef@databits.net> Cc: freebsd-doc@freebsd.org Subject: Re: Fw: Re: Bourne Shell Syntax Wierdness Message-ID: <200106290442.f5T4gLu02151@gilmore.nas.nasa.gov>
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petef@databits.net said:
>you first take 'true || true' -- you end up with true.
According to the man page, "||" is NOT "or". Instead it is an operator that
causes the command to its right to be executed only if the simple command to
its left fails. Therefore, 'true || true' means "continue without executing
the rightmost "true".
The (slightly dated) copy of POSIX.2 I have in my office actually calls the
following an "OR List," but says
command1 [ || command2 ] ...
means:
"First, command1 shall be executed. If its exit status is nonzero,
command2 xhall be executed, and so on until a command has a zero
exit status or there are no more commands left to execute."
Similarly, it calls the following an "AND List," but says
command1 [ && command2 ] ...
means:
"First, command1 shall be executed. If its exit status is zero,
command2 shall be executed, and so on until a command has a nonzero
exit status or there are no more commands left to execute. The
comnmands shall be expanded only if they are executed."
Curiously, POSIX says nothing about a list containing both operators.
--
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