EXEC(3) Linux Programmer's Manual EXEC(3)
NAME
execl, execlp, execle, execv, execvp - execute a file
SYNOPSIS
#include<unistd.h>
externchar**environ;
intexecl(constchar*path,constchar*arg,...);
intexeclp(constchar*file,constchar*arg,...);
intexecle(constchar*path,constchar*arg ,...,char*const
envp[]);
intexecv(constchar*path,char*const argv[]);
intexecvp(constchar*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 asso-
ciated 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 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 point-
ers must be terminated by a NULL pointer.
The execle function also specifies the environment of the executed pro-
cess by following the NULL pointer that terminates the list of argu-
ments in the parameter list or the pointer to the argv array with an
additional parameter. This additional parameter is an array of point-
ers 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 speci-
fied, the default path '':/bin:/usr/bin'' is used. In addition, cer-
tain errors are treated specially.
If permission is denied for a file (the attempted execve returned EAC-
CES), 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 search-
ing is done.)
RETURNVALUE
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 indi-
cate 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).
SEEALSO
sh(1), execve(2), fork(2), environ(5), ptrace(2)
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 possi-
bly 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.
CONFORMINGTO
execl, execv, execle, execlp and execvp conform to IEEE Std1003.1-88
(''POSIX.1'').
BSD MANPAGE 1993-11-29 EXEC(3)
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