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1.1 root 1: .th EXEC II 8/5/73
2: .sh NAME
3: exec \*- execute a file
4: .sh SYNOPSIS
5: (exec = 11.
6: .br
7: .ft B
8: sys exec; name; args
9: .br
10: .li
11: ...
12: .br
13: name: <...\\0>
14: .br
15: .li
16: ...
17: .br
18: args: arg1; arg2; ...; 0
19: .br
20: arg1: <...\\0>
21: .br
22: arg2: <...\\0>
23: .br
24: ...
25: .s3
26: execl(name, arg1, arg2, ..., argn, 0)
27: .br
28: char *name, *arg1, *arg2, ..., *argn;
29: .s3
30: execv(name, argv)
31: .br
32: char *name;
33: .br
34: char *argv[ ];
35: .ft R
36: .sh DESCRIPTION
37: .it Exec
38: overlays the calling process with the named file, then
39: transfers to the
40: beginning of the core image of the file.
41: There can be no return from the file; the calling
42: core image is lost.
43: .s3
44: Files remain open across
45: .it exec
46: calls.
47: Ignored signals remain ignored across
48: .it exec,
49: but
50: signals that are caught are reset
51: to their default values.
52: .s3
53: Each user has a
54: .it real
55: user ID and group ID and an
56: .it effective
57: user ID and group ID
58: (The
59: real
60: ID
61: identifies the person using the system;
62: the
63: effective
64: ID
65: determines his access privileges.)
66: .it Exec
67: changes the effective user and group ID to
68: the owner of the executed file if the file has the ``set-user-ID''
69: or ``set-group-ID''
70: modes.
71: The
72: real
73: user ID is not affected.
74: .s3
75: The form of this call differs somewhat depending
76: on whether it is called from assembly language or C;
77: see below for the C version.
78: .s3
79: The first argument to
80: .it exec
81: is a pointer to the name of the file
82: to be executed.
83: The second is the address of a null-terminated list of pointers to
84: arguments to be passed to the file.
85: Conventionally, the first argument is the name of the
86: file.
87: Each pointer addresses a string terminated by a null byte.
88: .s3
89: Once the called file starts execution, the arguments are available
90: as follows.
91: The stack pointer points to a word containing the number of arguments.
92: Just above
93: this number is a list of pointers to the argument strings.
94: The arguments are placed as high as possible in core.
95: .s3
96: sp\*> nargs
97: .br
98: arg1
99: .br
100: ...
101: .br
102: argn
103: .s3
104: arg1: <arg1\\0>
105: .br
106: ...
107: .br
108: argn: <argn\\0>
109: .s3
110: From C, two intefaces are available.
111: .it execl
112: is useful when a known file with known arguments is
113: being called;
114: the arguments to
115: .it execl
116: are the character strings
117: constituting the file and the arguments; as in
118: the basic call, the first argument is conventionally
119: the same as the file name (or its last component).
120: A 0 argument must end the argument list.
121: .s3
122: The
123: .it execv
124: version is useful when the number of arguments is unknown
125: in advance;
126: the arguments to
127: .it execv
128: are the name of the file to be
129: executed and a vector of strings containing
130: the arguments.
131: The last argument string must be followed
132: by a 0 pointer.
133: .s3
134: When a C program is executed,
135: it is called as follows:
136: .s3
137: main(argc, argv)
138: .br
139: int argc;
140: .br
141: char *argv[];
142: .s3
143: where \fIargc\fR is the argument count
144: and \fIargv\fR is an array of character pointers
145: to the arguments themselves.
146: As indicated, \fIargc\fR is conventionally at least one
147: and the first member of the array points to a
148: string containing the name of the file.
149: .s3
150: .it Argv
151: is not directly usable in another
152: .it execv,
153: since
154: .it argv[argc]
155: is \*-1 and not 0.
156: .sh "SEE ALSO"
157: fork(II)
158: .sh DIAGNOSTICS
159: If the file cannot be found,
160: if it is not executable,
161: if it does not have a valid header (407 or 410 octal as first word),
162: if maximum memory is exceeded,
163: or if the arguments require more than 512 bytes
164: a return from
165: .it exec
166: constitutes the diagnostic;
167: the error bit (c-bit) is set.
168: From C the returned value is \*-1.
169: .sh BUGS
170: Only 512 characters of arguments are allowed.
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