1exec(3) Library Functions Manual exec(3)
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6 execl, execlp, execle, execv, execvp, execvpe - execute a file
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9 Standard C library (libc, -lc)
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12 #include <unistd.h>
13 extern char **environ;
15 int execl(const char *pathname, const char *arg, ...
17 /*, (char *) NULL */);
18 int execlp(const char *file, const char *arg, ...
19 /*, (char *) NULL */);
20 int execle(const char *pathname, const char *arg, ...
21 /*, (char *) NULL, char *const envp[] */);
22 int execv(const char *pathname, char *const argv[]);
23 int execvp(const char *file, char *const argv[]);
24 int execvpe(const char *file, char *const argv[], char *const envp[]);
25 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
27 execvpe():
29 _GNU_SOURCE
30
32 The exec() family of functions replaces the current process image with
33 a new process image. The functions described in this manual page are
34 layered on top of execve(2). (See the manual page for execve(2) for
35 further details about the replacement of the current process image.)
36 The initial argument for these functions is the name of a file that is
38 to be executed.
39 The functions can be grouped based on the letters following the "exec"
41 prefix.
42 l - execl(), execlp(), execle()
44 The const char *arg and subsequent ellipses can be thought of as arg0,
45 arg1, ..., argn. Together they describe a list of one or more pointers
46 to null-terminated strings that represent the argument list available
47 to the executed program. The first argument, by convention, should
48 point to the filename associated with the file being executed. The
49 list of arguments must be terminated by a null pointer, and, since
50 these are variadic functions, this pointer must be cast (char *) NULL.
51 By contrast with the 'l' functions, the 'v' functions (below) specify
53 the command-line arguments of the executed program as a vector.
54 v - execv(), execvp(), execvpe()
56 The char *const argv[] argument is an array of pointers to null-termi‐
57 nated strings that represent the argument list available to the new
58 program. The first argument, by convention, should point to the file‐
59 name associated with the file being executed. The array of pointers
60 must be terminated by a null pointer.
61 e - execle(), execvpe()
63 The environment of the new process image is specified via the argument
64 envp. The envp argument is an array of pointers to null-terminated
65 strings and must be terminated by a null pointer.
66 All other exec() functions (which do not include 'e' in the suffix)
68 take the environment for the new process image from the external vari‐
69 able environ in the calling process.
70 p - execlp(), execvp(), execvpe()
72 These functions duplicate the actions of the shell in searching for an
73 executable file if the specified filename does not contain a slash (/)
74 character. The file is sought in the colon-separated list of directory
75 pathnames specified in the PATH environment variable. If this variable
76 isn't defined, the path list defaults to a list that includes the di‐
77 rectories returned by confstr(_CS_PATH) (which typically returns the
78 value "/bin:/usr/bin") and possibly also the current working directory;
79 see NOTES for further details.
80 execvpe() searches for the program using the value of PATH from the
82 caller's environment, not from the envp argument.
83 If the specified filename includes a slash character, then PATH is ig‐
85 nored, and the file at the specified pathname is executed.
86 In addition, certain errors are treated specially.
88 If permission is denied for a file (the attempted execve(2) failed with
90 the error EACCES), these functions will continue searching the rest of
91 the search path. If no other file is found, however, they will return
92 with errno set to EACCES.
93 If the header of a file isn't recognized (the attempted execve(2)
95 failed with the error ENOEXEC), these functions will execute the shell
96 (/bin/sh) with the path of the file as its first argument. (If this
97 attempt fails, no further searching is done.)
98 All other exec() functions (which do not include 'p' in the suffix)
100 take as their first argument a (relative or absolute) pathname that
101 identifies the program to be executed.
102
104 The exec() functions return only if an error has occurred. The return
105 value is -1, and errno is set to indicate the error.
106
108 All of these functions may fail and set errno for any of the errors
109 specified for execve(2).
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 The default search path (used when the environment does not contain the
125 variable PATH) shows some variation across systems. It generally in‐
126 cludes /bin and /usr/bin (in that order) and may also include the cur‐
127 rent working directory. On some other systems, the current working is
128 included after /bin and /usr/bin, as an anti-Trojan-horse measure. The
129 glibc implementation long followed the traditional default where the
130 current working directory is included at the start of the search path.
131 However, some code refactoring during the development of glibc 2.24
132 caused the current working directory to be dropped altogether from the
133 default search path. This accidental behavior change is considered
134 mildly beneficial, and won't be reverted.
135 The behavior of execlp() and execvp() when errors occur while attempt‐
137 ing to execute the file is historic practice, but has not traditionally
138 been documented and is not specified by the POSIX standard. BSD (and
139 possibly other systems) do an automatic sleep and retry if ETXTBSY is
140 encountered. Linux treats it as a hard error and returns immediately.
141 Traditionally, the functions execlp() and execvp() ignored all errors
143 except for the ones described above and ENOMEM and E2BIG, upon which
144 they returned. They now return if any error other than the ones de‐
145 scribed above occurs.
146
148 environ
149 execl()
150 execlp()
151 execle()
152 execv()
153 execvp()
154 POSIX.1-2008.
155 execvpe()
157 GNU.
158
160 environ
161 execl()
162 execlp()
163 execle()
164 execv()
165 execvp()
166 POSIX.1-2001.
167 execvpe()
169 glibc 2.11.
170
172 Before glibc 2.24, execl() and execle() employed realloc(3) internally
173 and were consequently not async-signal-safe, in violation of the re‐
174 quirements of POSIX.1. This was fixed in glibc 2.24.
175 Architecture-specific details
177 On sparc and sparc64, execv() is provided as a system call by the ker‐
178 nel (with the prototype shown above) for compatibility with SunOS.
179 This function is not employed by the execv() wrapper function on those
180 architectures.
181
183 sh(1), execve(2), execveat(2), fork(2), ptrace(2), fexecve(3), sys‐
184 tem(3), environ(7)
185Linux man-pages 6.04 2023-03-30 exec(3)