Why does find print a leading './' if no paths are given?

Question

Why is it that find prints out a leading ./ to results if no paths are given?

$ find
./file1
./file2
./file3

What is the reason for not printing out this?

$ find
file1
file2
file3

Answer 1

The reason why you see this is because the developer of GNU find chose to provide a "reasonable" behavior for find when no path is given. In contrast, POSIX doesn't state that the parameter is optional:

The find utility shall recursively descend the directory hierarchy from each file specified by path, evaluating a Boolean expression composed of the primaries described in the OPERANDS section for each file encountered. Each path operand shall be evaluated unaltered as it was provided, including all trailing <slash> characters; all pathnames for other files encountered in the hierarchy shall consist of the concatenation of the current path operand, a <slash> if the current path operand did not end in one, and the filename relative to the path operand. The relative portion shall contain no dot or dot-dot components, no trailing characters, and only single <slash> characters between pathname components.

You can see the difference in the synopsis for each. GNU has (as is the convention) optional items in square brackets:

find [-H] [-L] [-P] [-D debugopts] [-Olevel] [starting-point...]
       [expression]

while POSIX doesn't indicate that it can be optional:

find [-H|-L] path... [operand_expression...]

In the GNU program, that's done in ftsfind.c:

  if (empty)
    {
      /*
       * We use a temporary variable here because some actions modify
       * the path temporarily.  Hence if we use a string constant,
       * we get a coredump.  The best example of this is if we say
       * "find -printf %H" (note, not "find . -printf %H").
       */
      char defaultpath[2] = ".";
      return find (defaultpath);
    }

and a literal "." is used for simplicity. So you'll see the same result with

find

and

find .

because (and POSIX agrees) the given path will be used to prefix the results (see above for concatenation).

With a little work, one could determine when the feature was first added; it was present in the initial creation of "findutils" in 1996 (see find.c):

+  /* If no paths are given, default to ".".  */
+  for (i = 1; i < argc && strchr ("-!(),", argv[i][0]) == NULL; i++)
+    process_top_path (argv[i]);
+  if (i == 1)
+    process_top_path (".");
+
+  exit (exit_status);
+}

From the changelog for find 3.8, this was apparently

Sat Dec 15 19:01:12 1990  David J. MacKenzie  (djm at egypt)

        * find.c (main), util.c (usage): Make directory args optional,
        defaulting to "."

Answer 2

Usually, one does post-processing of the files and, in that case, there can be a huge advantage to starting the filename with ./. In particular, if a file name starts with -, a subsequent command could interpret that filename an option. ./ avoids that.

As an example, consider a directory with these files:

$ ls
--link  --no-clobber

Now, imagine how this command would work if the file names were provided without the ./ in front:

$ find -type f -exec cp -t ../ {} +

We can illustrate the problem with find itself. Let's run it in the same directory as above. The following works:

$ find ./*
./--link
./--no-clobber

The following fails:

$ find *
find: unknown predicate `--link'
Try 'find --help' for more information.

Answer 3

The find command needs path(s) to search.  If we don't specify any, it uses the current directory (.) as its starting point.  Similarly, if you pass the path, e.g., /tmp, it considers that as its starting point.  And therefore the results.

If current directory:

        $ find
or
        $ find .

output:
        ./file1
        ./file2
        ./file3

If /tmp directory:

        $ find /tmp

output:
        /tmp/file4
        /tmp/file5

If abc directory under the current directory:

        $ find abc

output:
        abc/file6
        abc/file7

If multiple directories under the current directory:

        $ find fu bar

output:
        fu/file10
        fu/file11
        bar/file8
        bar/file9

Answer 4

If you do not specify a path, find command assumes the ${PWD} as the path and prints it out on its output. User not specifying the path doesn't change the way find works. And find always works with paths by default.