1EXEC(3) Linux Programmer's Manual EXEC(3)
2
6 execl, execlp, execle, execv, execvp - execute a file
7
9 #include <unistd.h>
10 extern char **environ;
12 int execl(const char *path, const char *arg, ...);
14 int execlp(const char *file, const char *arg, ...);
15 int execle(const char *path, const char *arg,
16 ..., char * const envp[]);
17 int execv(const char *path, char *const argv[]);
18 int execvp(const char *file, char *const argv[]);
19
21 The exec() family of functions replaces the current process image with
22 a new process image. The functions described in this manual page are
23 front-ends for execve(2). (See the manual page for execve(2) for fur‐
24 ther details about the replacement of the current process image.)
25 The initial argument for these functions is the pathname of a file
27 which is to be executed.
28 The const char *arg and subsequent ellipses in the execl(), execlp(),
30 and execle() functions can be thought of as arg0, arg1, ..., argn.
31 Together they describe a list of one or more pointers to null-termi‐
32 nated strings that represent the argument list available to the exe‐
33 cuted program. The first argument, by convention, should point to the
34 filename associated with the file being executed. The list of argu‐
35 ments must be terminated by a NULL pointer, and, since these are vari‐
36 adic functions, this pointer must be cast (char *) NULL.
37 The execv() and execvp() functions provide an array of pointers to
39 null-terminated strings that represent the argument list available to
40 the new program. The first argument, by convention, should point to
41 the filename associated with the file being executed. The array of
42 pointers must be terminated by a NULL pointer.
43 The execle() function also specifies the environment of the executed
45 process by following the NULL pointer that terminates the list of argu‐
46 ments in the argument list or the pointer to the argv array with an
47 additional argument. This additional argument is an array of pointers
48 to null-terminated strings and must be terminated by a NULL pointer.
49 The other functions take the environment for the new process image from
50 the external variable environ in the current process.
51 Special semantics for execlp() and execvp()
53 The functions execlp() and execvp() will duplicate the actions of the
54 shell in searching for an executable file if the specified filename
55 does not contain a slash (/) character. The search path is the path
56 specified in the environment by the PATH variable. If this variable
57 isn't specified, the default path ":/bin:/usr/bin" is used. In addi‐
58 tion, certain errors are treated specially.
59 If permission is denied for a file (the attempted execve(2) failed with
61 the error EACCES), these functions will continue searching the rest of
62 the search path. If no other file is found, however, they will return
63 with errno set to EACCES.
64 If the header of a file isn't recognized (the attempted execve(2)
66 failed with the error ENOEXEC), these functions will execute the shell
67 (/bin/sh) with the path of the file as its first argument. (If this
68 attempt fails, no further searching is done.)
69
71 If any of the exec() functions returns, an error will have occurred.
72 The return value is -1, and errno will be set to indicate the error.
73
75 All of these functions may fail and set errno for any of the errors
76 specified for the library function execve(2).
77
79 POSIX.1-2001.
80
82 On some other systems the default path (used when the environment does
83 not contain the variable PATH) has the current working directory listed
84 after /bin and /usr/bin, as an anti-Trojan-horse measure. Linux uses
85 here the traditional "current directory first" default path.
86 The behavior of execlp() and execvp() when errors occur while attempt‐
88 ing to execute the file is historic practice, but has not traditionally
89 been documented and is not specified by the POSIX standard. BSD (and
90 possibly other systems) do an automatic sleep and retry if ETXTBSY is
91 encountered. Linux treats it as a hard error and returns immediately.
92 Traditionally, the functions execlp() and execvp() ignored all errors
94 except for the ones described above and ENOMEM and E2BIG, upon which
95 they returned. They now return if any error other than the ones
96 described above occurs.
97
99 sh(1), execve(2), fork(2), ptrace(2), fexecve(3), environ(7)
100
102 This page is part of release 3.25 of the Linux man-pages project. A
103 description of the project, and information about reporting bugs, can
104 be found at http://www.kernel.org/doc/man-pages/.
105GNU 2009-02-22 EXEC(3)