find -delete Command Deletes All Files Recursively – Why

filesfind

So the following behaviour of unix find just cost me dearly:

> touch foo
> touch bar
> ls  
bar  foo
> find . -name '*oo' -delete
> ls
bar
> touch baz
> ls
bar  baz
> find . -delete -name '*ar'
> ls
> #WHAAAT?

How does this make sense?

Best Answer

The command line of find is made from different kinds of options, that are combined to form expressions.

The find option -delete is an action.
That means it is executed for each file matched so far.
As first option after the paths, all files are matched... oops!

It is dangerous - but the man page at least has a big warning:

From man find:

ACTIONS
    -delete
           Delete  files; true if removal succeeded.  If the removal failed, an
           error message is issued.  If -delete fails, find's exit status  will
           be nonzero (when it eventually exits).  Use of -delete automatically
           turns on the -depth option.

           Warnings: Don't forget that the find command line is evaluated as an
           expression,  so  putting  -delete first will make find try to delete
           everything below the starting points you specified.  When testing  a
           find  command  line  that  you later intend to use with -delete, you
           should explicitly specify -depth in order to avoid later  surprises.
           Because  -delete  implies -depth, you cannot usefully use -prune and
           -delete together.


From further up in man find:

EXPRESSIONS
    The expression is made up of options (which affect overall operation rather
    than  the  processing  of  a  specific file, and always return true), tests
    (which return a true or false value), and actions (which have side  effects
    and  return  a  true  or false value), all separated by operators.  -and is
    assumed where the operator is omitted.

    If the expression contains no actions other than  -prune,  -print  is  per‐
    formed on all files for which the expression is true.


On trying out what a find command will do:

To see what a command like 

find . -name '*ar' -delete

will delete, you can first replace the action -delete by a more harmless action - like -fls or -print:

find . -name '*ar' -print

This will print which files are affected by the action.
In this example, the -print can be left out. In this case, there is not action at all, so the most obvious is added implicitly: -print. (See the second paragraph of the section "EXPRESSIONS" cited above)

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