GNU `make'

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#### The `vpath` Directive

Similar to the `VPATH` variable, but more selective, is the `vpath` directive (note lower case), which allows you to specify a search path for a particular class of file names: those that match a particular pattern. Thus you can supply certain search directories for one class of file names and other directories (or none) for other file names.

There are three forms of the `vpath` directive:

`vpath` pattern`` directories``
  Specify the search path directories for file names that match pattern.

  The search path, directories, is a list of directories to be searched, separated by colons (semi-colons on MS-DOS and MS-Windows) or blanks, just like the search path used in the `VPATH` variable.

`vpath` pattern``
  Clear out the search path associated with pattern.
`vpath`
  Clear all search paths previously specified with `vpath` directives.

A `vpath` pattern is a string containing a `%` character. The string must match the file name of a prerequisite that is being searched for, the `%` character matching any sequence of zero or more characters (as in pattern rules; see Defining and Redefining Pattern Rules). For example, `%.h` matches files that end in `.h`. (If there is no `%`, the pattern must match the prerequisite exactly, which is not useful very often.)

`%` characters in a `vpath` directive's pattern can be quoted with preceding backslashes (`\`). Backslashes that would otherwise quote `%` characters can be quoted with more backslashes. Backslashes that quote `%` characters or other backslashes are removed from the pattern before it is compared to file names. Backslashes that are not in danger of quoting `%` characters go unmolested.

When a prerequisite fails to exist in the current directory, if the pattern in a `vpath` directive matches the name of the prerequisite file, then the directories in that directive are searched just like (and before) the directories in the `VPATH` variable.

For example,

         vpath %.h ../headers

tells `make` to look for any prerequisite whose name ends in `.h` in the directory `../headers` if the file is not found in the current directory.

If several `vpath` patterns match the prerequisite file's name, then `make` processes each matching `vpath` directive one by one, searching all the directories mentioned in each directive. `make` handles multiple `vpath` directives in the order in which they appear in the makefile; multiple directives with the same pattern are independent of each other.

Thus,

         vpath %.c foo
         vpath %   blish
         vpath %.c bar

will look for a file ending in `.c` in `foo`, then `blish`, then `bar`, while

         vpath %.c foo:bar
         vpath %   blish

will look for a file ending in `.c` in `foo`, then `bar`, then `blish`.