3.7.2 Command Search and Execution
After a command has been split into words, if it results in a
simple command and an optional list of arguments, the following
actions are taken.
If the command name contains no slashes, the shell attempts to
locate it. If there exists a shell function by that name, that
function is invoked as described in section 3.3 Shell Functions.
If the name does not match a function, the shell searches for
it in the list of shell builtins. If a match is found, that
builtin is invoked.
If the name is neither a shell function nor a builtin,
and contains no slashes, Bash searches each element of
$PATH for a directory containing an executable file
by that name. Bash uses a hash table to remember the full
pathnames of executable files to avoid multiple
(see the description of
hash in section 4.1 Bourne Shell Builtins).
A full search of the directories in
is performed only if the command is not found in the hash table.
If the search is unsuccessful, the shell prints an error
message and returns an exit status of 127.
If the search is successful, or if the command name contains
one or more slashes, the shell executes the named program in
a separate execution environment.
Argument 0 is set to the name given, and the remaining arguments
to the command are set to the arguments supplied, if any.
If this execution fails because the file is not in executable
format, and the file is not a directory, it is assumed to be a
shell script and the shell executes it as described in
section 3.8 Shell Scripts.
If the command was not begun asynchronously, the shell waits for
the command to complete and collects its exit status.