execl, execlp, execle, execv, execvp - execute a file
extern char **environ;
execl(const char *path, const char *arg, ...);
execlp(const char *file, const char *arg, ...);
execle(const char *path, const char *arg, ..., char *const
execv(const char *path, char *const argv);
execvp(const char *file, char *const argv);
The exec family of functions replace the current process image with a new
process image. The functions described in this manual page
for the function execve(2). (See the manual page for
execve for detailed
information about the replacement of the current process.)
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(),
execle() functions can be thought of as arg0, arg1, ...,
they describe a list of one or more pointers to null-terminated strings
that represent the argument list available to the executed
first argument, by convention, should point to the file name
with the file being executed. The list of arguments must be
by a null pointer.
The execv() and execvp() functions provide an array of
pointers to nullterminated
strings that represent the argument list available to the new
program. The first argument, by convention, should point to
name associated with the file being executed. The array of
be terminated by a null pointer itself.
The execle() function also specifies the environment of the
by following the null pointer that terminates the list
in the parameter list or the pointer to the argv array with
parameter. This additional parameter is an array of pointers to nullterminated
strings and must be terminated by a null pointer
other functions take the environment for the new process image from the
external variable environ in the current process.
Some of these functions have special semantics.
The functions execlp() and execvp() will duplicate the actions of the
shell in searching for an executable file if the specified
file name does
not contain a slash (`/') character. The search path is the
in the environment by PATH variable. If this variable
_PATH_DEFPATH from <paths.h> is used instead, its value being:
In addition, certain errors are treated specially.
If permission is denied for a file (the attempted execve returned
EACCES), these functions will continue searching the rest of
path. If no other file is found, however, they will return
global variable errno set to EACCES.
If the header of a file isn't recognized (the attempted execve returned
ENOEXEC), these functions will execute the shell with the
path of the
file as its first argument. (If this attempt fails, no further searching
If the file is currently busy (the attempted execve returned
these functions will sleep for several seconds, periodically
to execute the file.
If any of the exec functions return, an error has occurred.
value is -1, and the global variable errno will be set to
/bin/sh default shell program
execl(), execle(), execlp(), and execvp() may fail and set
errno for any
of the errors specified for the library functions execve(2)
execv() may fail and set errno for any of the errors specified for the
library function execve(2).
sh(1), execve(2), fork(2), ktrace(2), ptrace(2), environ(7)
Historically, the default path for the execlp() and execvp()
was .:/bin:/usr/bin. This was changed to improve security
The behavior of execlp() and execvp() when errors occur
to execute the file is historic practice, but has not traditionally been
documented and is not specified by the POSIX standard.
Traditionally, the functions execlp() and execvp() ignored
all errors except
for the ones described above and ENOMEM and E2BIG, upon
returned. They now return if any error other than the ones
execl(), execv(), execle(), execlp() and execvp() conform to
OpenBSD 3.6 January 24, 1994
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