— Function: locate-file filename path &optional suffixes predicate

This function searches for a file whose name is filename in a list of directories given by path, trying the suffixes in suffixes. If it finds such a file, it returns the file's absolute file name (see Relative File Names); otherwise it returns nil.

The optional argument suffixes gives the list of file-name suffixes to append to filename when searching. locate-file tries each possible directory with each of these suffixes. If suffixes is nil, or (""), then there are no suffixes, and filename is used only as-is. Typical values of suffixes are exec-suffixes (see Subprocess Creation), load-suffixes, load-file-rep-suffixes and the return value of the function get-load-suffixes (see Load Suffixes).

Typical values for path are exec-path (see Subprocess Creation) when looking for executable programs, or load-path (see Library Search) when looking for Lisp files. If filename is absolute, path has no effect, but the suffixes in suffixes are still tried.

The optional argument predicate, if non-nil, specifies a predicate function for testing whether a candidate file is suitable. The predicate is passed the candidate file name as its single argument. If predicate is nil or omitted, locate-file uses file-readable-p as the predicate. See Kinds of Files, for other useful predicates, e.g., file-executable-p and file-directory-p.

This function will normally skip directories, so if you want it to find directories, make sure the predicate function returns dir-ok for them. For example:

          (locate-file "html" '("/var/www" "/srv") nil
                       (lambda (f) (if (file-directory-p f) 'dir-ok)))

For compatibility, predicate can also be one of the symbols executable, readable, writable, exists, or a list of one or more of these symbols.

— Function: executable-find program

This function searches for the executable file of the named program and returns the absolute file name of the executable, including its file-name extensions, if any. It returns nil if the file is not found. The functions searches in all the directories in exec-path, and tries all the file-name extensions in exec-suffixes (see Subprocess Creation).