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 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,
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 file
name associated with the file being executed. The list of
arguments must be terminated by a NULL pointer.
The execv and execvp functions provide an array of point
ers to null-terminated strings that represent the argument
list available to the new program. The first argument, by
convention, should point to the file name 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 termi
nates the list of arguments in the parameter list or the
pointer to the argv array with an additional parameter.
This additional parameter 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.
Some of these functions have special semantics.
specified file name does not contain a slash (/) charac
ter. The search path is the path specified in the envi
ronment 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
returned EACCES), these functions will continue searching
the rest of the search path. If no other file is found,
however, they will return with the 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 is done.)
If any of the exec functions returns, an error will have
occurred. The return value is -1, and the global variable
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).
sh(1), execve(2), fork(2), environ(5), ptrace(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 tra
ditional "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 returns immediately.
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.