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1.1 root 1: .\" Copyright (c) 1983 Regents of the University of California.
2: .\" All rights reserved. The Berkeley software License Agreement
3: .\" specifies the terms and conditions for redistribution.
4: .\"
5: .\" @(#)execvp.3 6.2 (Berkeley) 4/25/86
6: .\"
7: .TH EXECL 3 "April 25, 1986"
8: .UC 5
9: .SH NAME
10: execl, execv, execle, execlp, execvp, exec, execve, exect, environ \- execute a file
11: .SH SYNOPSIS
12: .nf
13: .B execl(name, arg0, arg1, ..., argn, 0)
14: .B char *name, *arg0, *arg1, ..., *argn;
15: .PP
16: .B execv(name, argv)
17: .B char *name, *argv[];
18: .PP
19: .B "execle(name, arg0, arg1, ..., argn, 0, envp)"
20: .B "char *name, *arg0, *arg1, ..., *argn, *envp[];"
21: .PP
22: .B "exect(name, argv, envp)
23: .B "char *name, *argv[], *envp[];
24: .PP
25: .B extern char **environ;
26: .fi
27: .SH DESCRIPTION
28: These routines provide various interfaces to the
29: .I execve
30: system call. Refer to
31: .IR execve (2)
32: for a description of their properties; only
33: brief descriptions are provided here.
34: .PP
35: .I Exec
36: in all its forms
37: overlays the calling process with the named file, then
38: transfers to the
39: entry point of the core image of the file.
40: There can be no return from a successful exec; the calling
41: core image is lost.
42: .PP
43: The
44: .I name
45: argument
46: is a pointer to the name of the file
47: to be executed.
48: The pointers
49: .IR arg [ 0 ],
50: .IR arg [ 1 "] ..."
51: address null-terminated strings.
52: Conventionally
53: .IR arg [ 0 ]
54: is the name of the
55: file.
56: .PP
57: Two interfaces are available.
58: .I execl
59: is useful when a known file with known arguments is
60: being called;
61: the arguments to
62: .I execl
63: are the character strings
64: constituting the file and the arguments;
65: the first argument is conventionally
66: the same as the file name (or its last component).
67: A 0 argument must end the argument list.
68: .PP
69: The
70: .I execv
71: version is useful when the number of arguments is unknown
72: in advance;
73: the arguments to
74: .I execv
75: are the name of the file to be
76: executed and a vector of strings containing
77: the arguments.
78: The last argument string must be followed
79: by a 0 pointer.
80: .PP
81: The
82: .I exect
83: version is used when the executed file is to be
84: manipulated with
85: .IR ptrace (2).
86: The program is forced to single step a single
87: instruction giving the parent an opportunity to
88: manipulate its state. On the VAX-11 this is done
89: by setting the trace bit in the process status
90: longword.
91: .PP
92: When a C program is executed,
93: it is called as follows:
94: .PP
95: .nf
96: main(argc, argv, envp)
97: int argc;
98: char **argv, **envp;
99: .fi
100: .PP
101: where
102: .I argc
103: is the argument count
104: and
105: .I argv
106: is an array of character pointers
107: to the arguments themselves.
108: As indicated,
109: .I argc
110: is conventionally at least one
111: and the first member of the array points to a
112: string containing the name of the file.
113: .PP
114: .I Argv
115: is directly usable in another
116: .I execv
117: because
118: .IR argv [ argc ]
119: is 0.
120: .PP
121: .I Envp
122: is a pointer to an array of strings that constitute
123: the
124: .I environment
125: of the process.
126: Each string consists of a name, an \*(lq=\*(rq, and a null-terminated value.
127: The array of pointers is terminated by a null pointer.
128: The shell
129: .IR sh (1)
130: passes an environment entry for each global shell variable
131: defined when the program is called.
132: See
133: .IR environ (7)
134: for some conventionally
135: used names.
136: The C run-time start-off routine places a copy of
137: .I envp
138: in the global cell
139: .IR environ ,
140: which is used
141: by
142: .I execv
143: and
144: .I execl
145: to pass the environment to any subprograms executed by the
146: current program.
147: .PP
148: .I Execlp
149: and
150: .I execvp
151: are called with the same arguments as
152: .I execl
153: and
154: .IR execv ,
155: but duplicate the shell's actions in searching for an executable
156: file in a list of directories.
157: The directory list is obtained from the environment.
158: .SH FILES
159: .ta \w'/bin/sh 'u
160: /bin/sh shell, invoked if command file found
161: by
162: .I execlp
163: or
164: .I execvp
165: .SH "SEE ALSO"
166: execve(2),
167: fork(2),
168: environ(7),
169: csh(1)
170: .SH DIAGNOSTICS
171: If the file cannot be found,
172: if it is not executable,
173: if it does not start with a valid magic number (see
174: .IR a.out (5)),
175: if maximum memory is exceeded,
176: or if the arguments require too much space,
177: a return
178: constitutes the diagnostic;
179: the return value is \-1.
180: Even for the super-user,
181: at least one of the execute-permission bits must be set for
182: a file to be executed.
183: .SH BUGS
184: If
185: .I execvp
186: is called to execute a file that turns out to be a shell
187: command file,
188: and if it is impossible to execute the shell,
189: the values of
190: .I argv[0]
191: and
192: .I argv[\-1]
193: will be modified before return.
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