1 /*
2 * DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
3 * Version 2, December 2004
4 *
5 * Copyright (C) 2019 Olaf Wintermann <olaf.wintermann@gmail.com>
6 *
7 * Everyone is permitted to copy and distribute verbatim or modified
8 * copies of this license document, and changing it is allowed as long
9 * as the name is changed.
10 *
11 * DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE
12 * TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
13 *
14 * 0. You just DO WHAT THE FUCK YOU WANT TO.
15 */
16
17 #include <stdio.h>
18 #include <stdlib.h>
19 #include <sys/stat.h>
20 #include <unistd.h>
21 #include <sys/fcntl.h>
22
23 #include <spawn.h>
24 #include <sys/wait.h>
25
26 int main(int argc, char **argv) {
27 int ret;
28
29 // create pipe for child process
30 // write to pout[1], read from pout[0]
31 int pout[2];
32 if(pipe(pout)) {
33 perror("pipe");
34 return 1;
35 }
36
37 // posix_spawn_file_actions_t defines actions on files of the child process
38 posix_spawn_file_actions_t actions;
39
40 // actions must be initialized with posix_spawn_file_actions_init
41 // and should be destroyed with posix_spawn_file_actions_destroy
42 posix_spawn_file_actions_init(&actions);
43
44 // possible actions:
45 // posix_spawn_file_actions_addclose
46 // closes a file descriptor in the child process
47 // posix_spawn_file_actions_addopen
48 // opens a file path
49 // posix_spawn_file_actions_adddup2
50 // performs dup2() on a file descriptor in the child process
51
52 // examples:
53
54 // close stdout in the child process
55 //posix_spawn_file_actions_addclose(&actions, 2);
56
57 // redirect stdout to a file
58 //posix_spawn_file_actions_addopen(&actions, 1, "out.txt", O_CREAT|O_WRONLY, 0644);
59
60 // redirect stdout to a pipe
61 posix_spawn_file_actions_adddup2(&actions, pout[1], 1);
62
63
64 // Attributes: unused in this example
65 //posix_spawnattr_t attr;
66 // init with posix_spawnattr_init
67 // free with posix_spawnattr_destroy
68 // can be used to speficy process attributes
69
70
71 // child command arguments
72 char *args[10];
73 args[0] = "/bin/printf";
74 args[1] = "%s\n%f\n%s\n";
75 args[2] = "Hello World";
76 args[3] = "3.14";
77 args[4] = "posix_spawn test";
78 args[5] = NULL; // array must be null-terminated
79
80 // child environment variables
81 char *env[10];
82 env[0] = "LC_ALL=C";
83 env[1] = NULL; // array must be null-terminated
84
85 // execute posix_spawn to create a child process
86 pid_t child;
87 ret = posix_spawn(
88 &child,
89 "/bin/printf",
90 &actions,
91 NULL, // attributes
92 args,
93 env);
94 posix_spawn_file_actions_destroy(&actions);
95 if(ret) {
96 // posix spawn failed
97 perror("posix_spawn");
98 return 1;
99 }
100
101 // close pout[1] (the write-part of the pipe) in the parent-process
102 // pout[1] is still open after that in the child-process
103 // if we don't close it here, read from pout[0] would never end
104 close(pout[1]);
105
106 // read the output of our child-process
107 char buf[1024];
108 ssize_t r;
109 int linestart = 1;
110 while((r=read(pout[0], buf, 1024)) > 0) {
111 // write every child-output line to stdout and customize the output
112 for(int i=0;i<r;i++) {
113 if(linestart) {
114 // add prefix to every output line
115 printf("stdout: [");
116 linestart = 0;
117 }
118 if(buf[i] == '\n') {
119 printf("]\n");
120 linestart = 1;
121 } else {
122 putchar(buf[i]);
123 }
124 }
125 }
126
127 // wait for the child to exit
128 int status;
129 waitpid(child, &status, 0);
130
131 return 0;
132 }
133
134