4 The run-command API offers a versatile tool to run sub-processes with
5 redirected input and output as well as with a modified environment
6 and an alternate current directory.
8 A similar API offers the capability to run a function asynchronously,
9 which is primarily used to capture the output that the function
10 produces in the caller in order to process it.
18 Start a sub-process. Takes a pointer to a `struct child_process`
19 that specifies the details and returns pipe FDs (if requested).
20 See below for details.
24 Wait for the completion of a sub-process that was started with
29 A convenience function that encapsulates a sequence of
30 start_command() followed by finish_command(). Takes a pointer
31 to a `struct child_process` that specifies the details.
33 `run_command_v_opt`, `run_command_v_opt_cd_env`::
35 Convenience functions that encapsulate a sequence of
36 start_command() followed by finish_command(). The argument argv
37 specifies the program and its arguments. The argument opt is zero
38 or more of the flags `RUN_COMMAND_NO_STDIN`, `RUN_GIT_CMD`,
39 `RUN_COMMAND_STDOUT_TO_STDERR`, or `RUN_SILENT_EXEC_FAILURE`
40 that correspond to the members .no_stdin, .git_cmd,
41 .stdout_to_stderr, .silent_exec_failure of `struct child_process`.
42 The argument dir corresponds the member .dir. The argument env
43 corresponds to the member .env.
45 The functions above do the following:
47 . If a system call failed, errno is set and -1 is returned. A diagnostic
50 . If the program was not found, then -1 is returned and errno is set to
51 ENOENT; a diagnostic is printed only if .silent_exec_failure is 0.
53 . Otherwise, the program is run. If it terminates regularly, its exit
54 code is returned. No diagnostic is printed, even if the exit code is
57 . If the program terminated due to a signal, then the return value is the
58 signal number + 128, ie. the same value that a POSIX shell's $? would
59 report. A diagnostic is printed.
64 Run a function asynchronously. Takes a pointer to a `struct
65 async` that specifies the details and returns a set of pipe FDs
66 for communication with the function. See below for details.
70 Wait for the completion of an asynchronous function that was
71 started with start_async().
76 The first argument is a pathname to an index file, or NULL
77 if the hook uses the default index file or no index is needed.
78 The second argument is the name of the hook.
79 The further arguments correspond to the hook arguments.
80 The last argument has to be NULL to terminate the arguments list.
81 If the hook does not exist or is not executable, the return
83 If it is executable, the hook will be executed and the exit
84 status of the hook is returned.
85 On execution, .stdout_to_stderr and .no_stdin will be set.
92 * `struct child_process`
94 This describes the arguments, redirections, and environment of a
95 command to run in a sub-process.
99 1. allocates and clears (memset(&chld, 0, sizeof(chld));) a
100 struct child_process variable;
101 2. initializes the members;
102 3. calls start_command();
103 4. processes the data;
104 5. closes file descriptors (if necessary; see below);
105 6. calls finish_command().
107 The .argv member is set up as an array of string pointers (NULL
108 terminated), of which .argv[0] is the program name to run (usually
109 without a path). If the command to run is a git command, set argv[0] to
110 the command name without the 'git-' prefix and set .git_cmd = 1.
112 Note that the ownership of the memory pointed to by .argv stays with the
113 caller, but it should survive until `finish_command` completes. If the
114 .argv member is NULL, `start_command` will point it at the .args
115 `argv_array` (so you may use one or the other, but you must use exactly
116 one). The memory in .args will be cleaned up automatically during
117 `finish_command` (or during `start_command` when it is unsuccessful).
119 The members .in, .out, .err are used to redirect stdin, stdout,
122 . Specify 0 to request no special redirection. No new file descriptor
123 is allocated. The child process simply inherits the channel from the
126 . Specify -1 to have a pipe allocated; start_command() replaces -1
127 by the pipe FD in the following way:
129 .in: Returns the writable pipe end into which the caller writes;
130 the readable end of the pipe becomes the child's stdin.
132 .out, .err: Returns the readable pipe end from which the caller
133 reads; the writable end of the pipe end becomes child's
136 The caller of start_command() must close the so returned FDs
137 after it has completed reading from/writing to it!
139 . Specify a file descriptor > 0 to be used by the child:
141 .in: The FD must be readable; it becomes child's stdin.
142 .out: The FD must be writable; it becomes child's stdout.
143 .err: The FD must be writable; it becomes child's stderr.
145 The specified FD is closed by start_command(), even if it fails to
148 . Special forms of redirection are available by setting these members
151 .no_stdin, .no_stdout, .no_stderr: The respective channel is
152 redirected to /dev/null.
154 .stdout_to_stderr: stdout of the child is redirected to its
155 stderr. This happens after stderr is itself redirected.
156 So stdout will follow stderr to wherever it is
159 To modify the environment of the sub-process, specify an array of
160 string pointers (NULL terminated) in .env:
162 . If the string is of the form "VAR=value", i.e. it contains '='
163 the variable is added to the child process's environment.
165 . If the string does not contain '=', it names an environment
166 variable that will be removed from the child process's environment.
168 To specify a new initial working directory for the sub-process,
169 specify it in the .dir member.
171 If the program cannot be found, the functions return -1 and set
172 errno to ENOENT. Normally, an error message is printed, but if
173 .silent_exec_failure is set to 1, no message is printed for this
174 special error condition.
179 This describes a function to run asynchronously, whose purpose is
180 to produce output that the caller reads.
184 1. allocates and clears (memset(&asy, 0, sizeof(asy));) a
185 struct async variable;
186 2. initializes .proc and .data;
187 3. calls start_async();
188 4. processes communicates with proc through .in and .out;
189 5. closes .in and .out;
190 6. calls finish_async().
192 The members .in, .out are used to provide a set of fd's for
193 communication between the caller and the callee as follows:
195 . Specify 0 to have no file descriptor passed. The callee will
196 receive -1 in the corresponding argument.
198 . Specify < 0 to have a pipe allocated; start_async() replaces
199 with the pipe FD in the following way:
201 .in: Returns the writable pipe end into which the caller
202 writes; the readable end of the pipe becomes the function's
205 .out: Returns the readable pipe end from which the caller
206 reads; the writable end of the pipe becomes the function's
209 The caller of start_async() must close the returned FDs after it
210 has completed reading from/writing from them.
212 . Specify a file descriptor > 0 to be used by the function:
214 .in: The FD must be readable; it becomes the function's in.
215 .out: The FD must be writable; it becomes the function's out.
217 The specified FD is closed by start_async(), even if it fails to
220 The function pointer in .proc has the following signature:
222 int proc(int in, int out, void *data);
224 . in, out specifies a set of file descriptors to which the function
225 must read/write the data that it needs/produces. The function
226 *must* close these descriptors before it returns. A descriptor
227 may be -1 if the caller did not configure a descriptor for that
230 . data is the value that the caller has specified in the .data member
233 . The return value of the function is 0 on success and non-zero
234 on failure. If the function indicates failure, finish_async() will
235 report failure as well.
238 There are serious restrictions on what the asynchronous function can do
239 because this facility is implemented by a thread in the same address
240 space on most platforms (when pthreads is available), but by a pipe to
241 a forked process otherwise:
243 . It cannot change the program's state (global variables, environment,
244 etc.) in a way that the caller notices; in other words, .in and .out
245 are the only communication channels to the caller.
247 . It must not change the program's state that the caller of the