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execl, execlp, execle, execv, execvp - execute a file
extern char **environ;
int execl(const char *path, const char *arg, ...);
int execlp(const char *file, const char *arg, ...);
int execle(const char *path, const char *arg,
..., char * const envp);
int execv(const char *path, char *const argv);
int execvp(const char *file, char *const argv);
The exec() family of functions replaces the current process image with
a new process image. The functions described in this manual page are
front-ends for execve(2). (See the manual page for execve(2) for
further details about the replacement of the current process image.)
The initial argument for these functions is the pathname of a file
which is to be executed.
The const char *arg and subsequent ellipses in the execl(), execlp(),
and execle() functions can be thought of as arg0, arg1, ..., argn.
Together they describe a list of one or more pointers to null-
terminated strings that represent the argument list available to the
executed program. The first argument, by convention, should point to
the filename associated with the file being executed. The list of
arguments must be terminated by a NULL pointer, and, since these are
variadic functions, this pointer must be cast (char *) NULL.
The execv() and execvp() functions provide an array of pointers to
null-terminated strings that represent the argument list available to
the new program. The first argument, by convention, should point to
the filename associated with the file being executed. The array of
pointers must be terminated by a NULL pointer.
The execle() function also specifies the environment of the executed
process by following the NULL pointer that terminates the list of
arguments in the argument list or the pointer to the argv array with an
additional argument. This additional argument is an array of pointers
to null-terminated strings and must be terminated by a NULL pointer.
The other functions take the environment for the new process image from
the external variable environ in the current process.
Special semantics for execlp() and execvp()
The functions execlp() and execvp() will duplicate the actions of the
shell in searching for an executable file if the specified filename
does not contain a slash (/) character. The search path is the path
specified in the environment by the PATH variable. If this variable
isn’t specified, the default path ":/bin:/usr/bin" is used. In
addition, certain errors are treated specially.
If permission is denied for a file (the attempted execve(2) failed with
the error EACCES), these functions will continue searching the rest of
the search path. If no other file is found, however, they will return
with errno set to EACCES.
If the header of a file isn’t recognized (the attempted execve(2)
failed with the error ENOEXEC), these functions will execute the shell
(/bin/sh) with the path of the file as its first argument. (If this
attempt fails, no further searching is done.)
If any of the exec() functions returns, an error will have occurred.
The return value is -1, and errno will be set to indicate the error.
All of these functions may fail and set errno for any of the errors
specified for the library function execve(2).
On some other systems the default path (used when the environment does
not contain the variable PATH) has the current working directory listed
after /bin and /usr/bin, as an anti-Trojan-horse measure. Linux uses
here the traditional "current directory first" default path.
The behavior of execlp() and execvp() when errors occur while
attempting to execute the file is historic practice, but has not
traditionally been documented and is not specified by the POSIX
standard. BSD (and possibly other systems) do an automatic sleep and
retry if ETXTBSY is encountered. Linux treats it as a hard error and
Traditionally, the functions execlp() and execvp() ignored all errors
except for the ones described above and ENOMEM and E2BIG, upon which
they returned. They now return if any error other than the ones
described above occurs.
sh(1), execve(2), fork(2), ptrace(2), fexecve(3), environ(7)
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description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.