Date: Tue, 20 May 2008 11:33:50 +0200 From: Jonathan McKeown <jonathan@hst.org.za> To: freebsd-questions@freebsd.org Subject: Re: Now what would you expect this to print out? Message-ID: <200805201133.50963.jonathan@hst.org.za> In-Reply-To: <20080520014133.3447c282@gumby.homeunix.com.> References: <7d6fde3d0805190149y7a3bfa75j2ca6a67cef66e8f6@mail.gmail.com> <20080519094603.GC12033@osiris.chen.org.nz> <20080520014133.3447c282@gumby.homeunix.com.>
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On Tuesday 20 May 2008 02:41, RW wrote: > On Mon, 19 May 2008 21:46:03 +1200 > > Jonathan Chen <jonc@chen.org.nz> wrote: > > On Mon, May 19, 2008 at 01:49:35AM -0700, Garrett Cooper wrote: > > > Riddle for the day for folks that have source trees... what would > > > you expect this to print out (ask yourself the question and then > > > execute the command)? > > > > > > find /usr/src -name Makefile -or -name '*.mk' -print > > > > > > The expected output and what actual output differed in my mind, but > > > maybe somebody else can "shed some light" on the logic behind what > > > happened > > > > It's a problem that catches many young players with find(1). One has > > to remember from reading the man-page that all directives have an > > implicit AND operator on it; and that includes the "-print" directive. > > So to get what you want, you have to introduce brackets: > > > > find /usr/src \( -name Makefile -or -name '*.mk' \) -print > > Why does that make a difference, when print always evaluates to true? > > x AND true = x > > so > > (a OR b) AND true = a OR b > a OR (b AND true) = a OR b It makes a difference (as in programming) because -print is used for its side-effect rather than its value, and the binding order influences when the side-effect happens. Jonathan
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