Is -print a useless option for find now?

Looking at the man page under FreeBSD, I see:

 -print  This primary always evaluates to true.  It prints the pathname of
         the current file to standard output.  If none of -exec, -ls,
         -print0, or -ok is specified, the given expression shall be
         effectively replaced by ( given expression ) -print.

So in many cases, -print is unnecessary. However, consider this expression that looks for a file named foo inside of somedir, but not inside any directory named .snapshot:

find somedir -name .snapshot -prune -o -name foo

Given the description referenced above, this will be transformed into:

find somedir ( -name .snapshot -prune -o -name foo ) -print

Which is not the same as what was probably intended:

find somedir -name .snapshot -prune -o -name foo -print

Adding parentheses to make the group a bit more obvious, this is:

find somedir ( -name .snapshot -prune ) -o ( -name foo -print )

To spot the difference, notice that both -prune and -print evaluate to true. So without specifying -print, the first version will print out the current file if either -name .snapshot or -name foo matches.

The second version will only output the current file if -name foo matches.

This is a long winded way of saying that -print is not generally necessary as long as you understand the situations in which it is necessary.

larsks

Posted 2011-06-14T02:22:21.773

Reputation: 3 245

Incidentally, this was fun. I hadn't realized the subtleties of this before. Thanks, locale! – larsks – 2011-06-14T02:50:53.523

@larsks,what does it mean by This primary always evaluates to true? – None – 2011-06-14T03:04:03.657

@locale: Exactly what it says. find is a huge logical expression evaluator, and some of its predicates have side effects as well as returning a boolean value. – Ignacio Vazquez-Abrams – 2011-06-14T03:14:19.503

You give find a bunch of boolean expressions -- like -name foo, which evaluates to True when a file is named foo. Expressions like -print or -prune don't really specify a condition, so they always evaluate to True. – larsks – 2011-06-14T03:27:36.647

@larsks,why don't just use -print since they always evalutes to true,isn't it duplicate? – None – 2011-06-14T03:30:35.010

I'm not sure I understand your last question. – larsks – 2011-06-14T03:47:19.507

@locale, I think it means that the options can have two outcomes. Firstly they evaluate to true/false as part of deciding if a file "matches". Secondly they have side effects, like printing the name of the file. -print is only used for this side-effect so the boolean value is set to true. If it were set to false, later options (whose side effects you want) might not get evaluated. Consider find . -name foo -mtime 3 -print -exec touch {} \; if -print were false, a typical short-circuit evaluation algorithm would not evaluate the -exec. There is an implicit "and" between the options. – RedGrittyBrick – 2011-06-14T10:58:09.063

Is -print a useless option for find now?

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