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1.1 root 1: .TH EXEC 2
2: .CT 2 proc_man
3: .SH NAME
4: execl, execv, execle, execve, execlp, execvp, exect \(mi execute a file
5: .SH SYNOPSIS
6: .nf
7: .B int "execl(name, arg0, arg1, ..., argn, (char *)0)"
8: .B char *name, *arg0, *arg1, ..., *argn;
9: .PP
10: .B int execv(name, argv)
11: .B char *name, *argv[];
12: .PP
13: .B "int execle(name, arg0, arg1, ..., argn, (char *)0, envp)"
14: .B "char *name, *arg0, *arg1, ..., *argn, *envp[];"
15: .PP
16: .B int execve(name, argv, envp)
17: .B char *name, *argv[], *envp[];
18: .PP
19: .B int "execlp(name, arg0, arg1, ..., argn, (char *)0)"
20: .B char *name, *arg0, *arg1, ..., *argn;
21: .PP
22: .B int execvp(name, argv)
23: .B char *name, *argv[];
24: .PP
25: .B int exect(name, argv, envp)
26: .B char *name, *argv[], *envp[];
27: .fi
28: .SH DESCRIPTION
29: .I Exec
30: in all its forms
31: overlays the calling process with the named file, then
32: transfers to the
33: entry point of the image of the file.
34: There can be no return from a successful
35: .IR exec ;
36: the calling image is lost.
37: .PP
38: Files remain open across
39: .I exec
40: unless explicit arrangement has been made;
41: see
42: .IR ioctl (2).
43: Signals that are caught (see
44: .IR signal (2))
45: are reset
46: to their default values.
47: Other signal settings
48: are unchanged.
49: .PP
50: Each user has a
51: .I real
52: userid and groupid and an
53: .I effective
54: userid and groupid.
55: The real userid (groupid)
56: identifies the person using the system;
57: the effective userid (groupid)
58: determines access privileges.
59: .I Exec
60: changes the effective userid and groupid to
61: the owner of the executed file if the file has the set-userid
62: or set-groupid modes.
63: The real userid is not affected.
64: .PP
65: .I Name
66: points to the name of the file
67: to be executed.
68: It must be a regular file
69: (type
70: .BR S_IFREG ,
71: see
72: .IR stat (2))
73: and its permissions must allow execution.
74: .I Arg0, arg1, ...
75: or the pointers in
76: .I argv
77: address null-terminated argument strings
78: to be made available when the new image starts.
79: .I Argv
80: must end with a 0 pointer.
81: Conventionally argument 0
82: is the name of the program.
83: .PP
84: In
85: .IR execle ,
86: .IR execve ,
87: and
88: .IR exect ,
89: the
90: .I envp
91: array contains pointers to
92: a set of null-terminated strings
93: composing the environment of the process.
94: .I Envp
95: must end with a 0 pointer.
96: The other calls
97: copy the present environment
98: from the global cell
99: .IR environ ;
100: see
101: .IR environ (5).
102: .PP
103: The
104: .I execl
105: and
106: .I execv
107: forms
108: differ only in argument syntax;
109: one is more convenient when the number of arguments is known in advance,
110: the other when arguments are assembled on the fly.
111: .PP
112: If the first two bytes of the file
113: are the characters
114: .LR #! ,
115: subsequent text up to a newline is examined.
116: The first word,
117: up to a blank or tab,
118: names an interpreter program;
119: anything left over is a single supplemental argument.
120: The original
121: .IR name ,
122: preceded by the supplemental argument if any,
123: is inserted in the argument list
124: between
125: .I arg0
126: and
127: .I arg1
128: (or between the first pair of
129: .I argv
130: pointers).
131: The interpreter is executed with the modified argument list.
132: .PP
133: If the file doesn't start with
134: .LR #! ,
135: a standard header for
136: a binary image
137: is expected;
138: see
139: .IR a.out (5).
140: If the file doesn't begin with a valid header either,
141: .B ENOEXEC
142: is returned.
143: The shell
144: .IR sh (1)
145: takes this to mean that the file
146: contains shell commands.
147: .PP
148: When a C program is executed,
149: it is called as follows:
150: .IP
151: .EX
152: main(argc, argv, envp)
153: int argc;
154: char **argv, **envp;
155: .EE
156: .PP
157: .I Argv
158: is the array of argument pointers passed to
159: .IR exec ;
160: .I argc
161: is the number of arguments.
162: .I Argv
163: is directly usable in a subsequent
164: .I execv
165: because
166: .BR argv[argc]==0 .
167: .I Envp
168: is the environment array;
169: the same value has already been stored in
170: .IR environ .
171: .PP
172: .I Execlp
173: and
174: .I execvp
175: take the same arguments as
176: .I execl
177: and
178: .IR execv ,
179: but search the directories listed in the
180: .B PATH
181: environment variable
182: for an executable file called
183: .IR name ,
184: mimicking the shell's path search.
185: .PP
186: .I Exect
187: is the same as
188: .IR execve ,
189: except that it arranges for the process to stop
190: just before the first instruction of the new image;
191: see
192: .IR proc (4).
193: .SH FILES
194: .TF /bin/sh
195: .TP
196: .F /bin/sh
197: shell, invoked if command file found
198: by
199: .I execlp
200: or
201: .I execvp
202: .SH EXAMPLES
203: This file,
204: if created with execute permissions
205: and run by
206: .IR exec ,
207: calls
208: .IR awk (1)
209: to count the lines in all the files named in its arguments:
210: .EX
211: #!/usr/bin/awk -f
212: END { print NR }
213: .EE
214: .SH "SEE ALSO"
215: .IR sh (1),
216: .IR fork (2),
217: .IR ioctl (2),
218: .IR signal (2),
219: .IR proc (4),
220: .IR environ (5)
221: .SH DIAGNOSTICS
222: .BR E2BIG ,
223: .BR EACCES ,
224: .BR EFAULT ,
225: .BR EIO ,
226: .BR ELOOP ,
227: .BR ENOENT ,
228: .BR ENOEXEC ,
229: .BR ENOMEM ,
230: .BR ENOTDIR ,
231: .BR ENXIO ,
232: .BR ETXTBSY
233: .SH BUGS
234: If
235: .I execvp
236: is called to execute a file that turns out to be a shell
237: command file,
238: and the shell cannot be executed,
239: some of the values in
240: .I argv
241: may be modified before return.
242: .br
243: Neither the shell's path search
244: nor that of
245: .I execlp
246: and
247: .I execvp
248: extends to the interpreter named after
249: .LR #! .
250: The interpreter file
251: may not itself begin with
252: .LR #! .
253: The text after
254: .LR #!
255: may be no more than 30 characters long,
256: including the newline.
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