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NAME
execl, execlp, execle, execv, execvp - execute a file
SYNOPSIS
#include <unistd.h>
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[]);
DESCRIPTION
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, 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 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 terminates 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.
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 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() 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.)
RETURN VALUE
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.
FILES
/bin/sh
ERRORS
All of these functions may fail and set errno for any of the errors
specified for the library function execve(2).
SEE ALSO
sh(1), execve(2), fork(2), ptrace(2), environ(5)
COMPATIBILITY
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
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.
CONFORMING TO
execl(), execv(), execle(), execlp() and execvp() conform to IEEE
Std1003.1-88 (‘‘POSIX.1’’).