1EXEC(3) Linux Programmer's Manual EXEC(3)
2
6 execl, execlp, execle, execv, execvp, execvpe - execute a file
7
9 #include <unistd.h>
10 extern char **environ;
12 int execl(const char *pathname, const char *arg, ...
14 /*, (char *) NULL */);
15 int execlp(const char *file, const char *arg, ...
16 /*, (char *) NULL */);
17 int execle(const char *pathname, const char *arg, ...
18 /*, (char *) NULL, char *const envp[] */);
19 int execv(const char *pathname, char *const argv[]);
20 int execvp(const char *file, char *const argv[]);
21 int execvpe(const char *file, char *const argv[], char *const envp[]);
22 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
24 execvpe():
26 _GNU_SOURCE
27
29 The exec() family of functions replaces the current process image with
30 a new process image. The functions described in this manual page are
31 layered on top of execve(2). (See the manual page for execve(2) for
32 further details about the replacement of the current process image.)
33 The initial argument for these functions is the name of a file that is
35 to be executed.
36 The functions can be grouped based on the letters following the "exec"
38 prefix.
39 l - execl(), execlp(), execle()
41 The const char *arg and subsequent ellipses can be thought of as arg0,
42 arg1, ..., argn. Together they describe a list of one or more pointers
43 to null-terminated strings that represent the argument list available
44 to the executed program. The first argument, by convention, should
45 point to the filename associated with the file being executed. The
46 list of arguments must be terminated by a null pointer, and, since
47 these are variadic functions, this pointer must be cast (char *) NULL.
48 By contrast with the 'l' functions, the 'v' functions (below) specify
50 the command-line arguments of the executed program as a vector.
51 v - execv(), execvp(), execvpe()
53 The char *const argv[] argument is an array of pointers to null-termi‐
54 nated strings that represent the argument list available to the new
55 program. The first argument, by convention, should point to the file‐
56 name associated with the file being executed. The array of pointers
57 must be terminated by a null pointer.
58 e - execle(), execvpe()
60 The environment of the new process image is specified via the argument
61 envp. The envp argument is an array of pointers to null-terminated
62 strings and must be terminated by a null pointer.
63 All other exec() functions (which do not include 'e' in the suffix)
65 take the environment for the new process image from the external vari‐
66 able environ in the calling process.
67 p - execlp(), execvp(), execvpe()
69 These functions duplicate the actions of the shell in searching for an
70 executable file if the specified filename does not contain a slash (/)
71 character. The file is sought in the colon-separated list of directory
72 pathnames specified in the PATH environment variable. If this variable
73 isn't defined, the path list defaults to a list that includes the di‐
74 rectories returned by confstr(_CS_PATH) (which typically returns the
75 value "/bin:/usr/bin") and possibly also the current working directory;
76 see NOTES for further details.
77 execvpe() searches for the program using the value of PATH from the
79 caller's environment, not from the envp argument.
80 If the specified filename includes a slash character, then PATH is ig‐
82 nored, and the file at the specified pathname is executed.
83 In addition, certain errors are treated specially.
85 If permission is denied for a file (the attempted execve(2) failed with
87 the error EACCES), these functions will continue searching the rest of
88 the search path. If no other file is found, however, they will return
89 with errno set to EACCES.
90 If the header of a file isn't recognized (the attempted execve(2)
92 failed with the error ENOEXEC), these functions will execute the shell
93 (/bin/sh) with the path of the file as its first argument. (If this
94 attempt fails, no further searching is done.)
95 All other exec() functions (which do not include 'p' in the suffix)
97 take as their first argument a (relative or absolute) pathname that
98 identifies the program to be executed.
99
101 The exec() functions return only if an error has occurred. The return
102 value is -1, and errno is set to indicate the error.
103
105 All of these functions may fail and set errno for any of the errors
106 specified for execve(2).
107
109 The execvpe() function first appeared in glibc 2.11.
110
112 For an explanation of the terms used in this section, see at‐
113 tributes(7).
114 ┌────────────────────────────────────────┬───────────────┬─────────────┐
116 │Interface │ Attribute │ Value │
117 ├────────────────────────────────────────┼───────────────┼─────────────┤
118 │execl(), execle(), execv() │ Thread safety │ MT-Safe │
119 ├────────────────────────────────────────┼───────────────┼─────────────┤
120 │execlp(), execvp(), execvpe() │ Thread safety │ MT-Safe env │
121 └────────────────────────────────────────┴───────────────┴─────────────┘
122
124 POSIX.1-2001, POSIX.1-2008.
125 The execvpe() function is a GNU extension.
127
129 The default search path (used when the environment does not contain the
130 variable PATH) shows some variation across systems. It generally in‐
131 cludes /bin and /usr/bin (in that order) and may also include the cur‐
132 rent working directory. On some other systems, the current working is
133 included after /bin and /usr/bin, as an anti-Trojan-horse measure. The
134 glibc implementation long followed the traditional default where the
135 current working directory is included at the start of the search path.
136 However, some code refactoring during the development of glibc 2.24
137 caused the current working directory to be dropped altogether from the
138 default search path. This accidental behavior change is considered
139 mildly beneficial, and won't be reverted.
140 The behavior of execlp() and execvp() when errors occur while attempt‐
142 ing to execute the file is historic practice, but has not traditionally
143 been documented and is not specified by the POSIX standard. BSD (and
144 possibly other systems) do an automatic sleep and retry if ETXTBSY is
145 encountered. Linux treats it as a hard error and returns immediately.
146 Traditionally, the functions execlp() and execvp() ignored all errors
148 except for the ones described above and ENOMEM and E2BIG, upon which
149 they returned. They now return if any error other than the ones de‐
150 scribed above occurs.
151
153 Before glibc 2.24, execl() and execle() employed realloc(3) internally
154 and were consequently not async-signal-safe, in violation of the re‐
155 quirements of POSIX.1. This was fixed in glibc 2.24.
156 Architecture-specific details
158 On sparc and sparc64, execv() is provided as a system call by the ker‐
159 nel (with the prototype shown above) for compatibility with SunOS.
160 This function is not employed by the execv() wrapper function on those
161 architectures.
162
164 sh(1), execve(2), execveat(2), fork(2), ptrace(2), fexecve(3), sys‐
165 tem(3), environ(7)
166
168 This page is part of release 5.13 of the Linux man-pages project. A
169 description of the project, information about reporting bugs, and the
170 latest version of this page, can be found at
171 https://www.kernel.org/doc/man-pages/.
172GNU 2021-03-22 EXEC(3)