— 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 full absolute file name of the file (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 exec-suffixes), 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 exec-path) when looking for executable programs or load-path (see load-path) 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 the predicate function to use for testing whether a candidate file is suitable. The predicate function is passed the candidate file name as its single argument. If predicate is nil or unspecified, locate-file uses file-readable-p as the default predicate. Useful non-default predicates include file-executable-p, file-directory-p, and other predicates described in Kinds of Files.

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 full absolute 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.