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66 lines
2.7 KiB
Markdown
66 lines
2.7 KiB
Markdown
## Name
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posix\_spawn - launch a new process
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## Synopsis
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```**c++
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#include <spawn.h>
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int posix_spawn(pid_t* pid, const char* executable_path, const posix_spawn_file_actions_t*, const posix_spawnattr_t*, char* const argv[], char* const envp[]);
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int posix_spawnp(pid_t* pid, const char* executable_path, const posix_spawn_file_actions_t*, const posix_spawnattr_t*, char* const argv[], char* const envp[]);
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```
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## Description
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Spawn a new process reading the binary `executable_path`, passing `argv` as arguments to `main()` and setting `envp` as argument.
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Places the process ID of the new process in `pid`.
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If `executable_path` passed to `posix_spawn` is a relative path, it is resolved relative to the current working directory.
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If `executable_path` passed to `posix_spawnp` is a relative path, it is resolved by searching through directories specified in the `PATH` environment variable.
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The `posix_spawn_file_actions_t` and `posix_spawnattr_t` arguments may be `nullptr`. If they aren't, see [`posix_spawn_file_actions`(2)](help://man/3/posix_spawn_file_actions_init) and [`posix_spawnattr`(2)](help://man/3/posix_spawnattr_init) for what they do.
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The last entry in `argv` and `envp` has to be `nullptr`.
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The new process is started as if the following steps are executed in this order:
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1. A new process is started as if `fork()` was called.
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2. If the `posix_spawnattr_t` parameter is non-nullptr, it [takes effect](help://man/3/posix_spawnattr_init).
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3. If the `posix_spawn_file_actions_t` parameter is non-nullptr, it [takes effect](help://man/3/posix_spawn_file_actions_init).
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4. `executable_path` is loaded and starts running, as if `execve` or `execvpe` was called.
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## Return value
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If the process is successfully forked, returns 0.
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Otherwise, returns an error number. This function does *not* return -1 on error and does *not* set `errno` like most other functions, it instead returns what other functions set `errno` to as result.
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If the process forks successfully but spawnattr or file action processing or exec fail, `posix_spawn` returns 0 and the child exits with exit code `127`.
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## Example
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This simple example launches `/bin/Calculator`.
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To make the child process use the parent's environment, it passes `environ` from `unistd.h`.
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```**c++
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#include <errno.h>
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#include <unistd.h>
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#include <stdio.h>
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#include <spawn.h>
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int main()
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{
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const char* argv[] = { "Calculator", nullptr };
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pid_t child_pid;
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if ((errno = posix_spawn(&child_pid, "/bin/Calculator", nullptr, nullptr, const_cast<char**>(argv), environ)))
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perror("posix_spawn");
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}
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```
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## See also
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* [`posix_spawnattr`(2)](help://man/3/posix_spawnattr_init)
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* [`posix_spawn_file_actions`(2)](help://man/3/posix_spawn_file_actions_init)
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