| 词条 | Dup (system call) |
| 释义 |
In Unix-like operating systems, dup (short for "duplicate") and dup2 system calls create a copy of a given file descriptor. This new descriptor actually does not behave like a copy, but like an alias of the old one. C library POSIX definitionThe dup and dup2 calls are standardized by the POSIX specification.[1] int dup (int oldfd); int dup2 (int oldfd, int newfd); The former allocates the first available descriptor, just like open() behaves; an alternative way to duplicate a file descriptor to an unspecified place is the fcntl system call with The latter places the copy into newfd. If newfd is open, it is closed first. dup2 for input/output redirection{{expand section|date=March 2012}}Unix shells use dup2 for input/output redirection. Along with The following example uses
/* function prototypes */ void die(const char*); int main(int argc, char **argv) { int pdes[2]; pid_t child; if(pipe(pdes) == -1) die("pipe()"); child = fork(); if(child == (pid_t)(-1)) die("fork()"); /* fork failed */ if(child == (pid_t)0) { close(1); /* close stdout */ if(dup(pdes[1]) == -1) die("dup()"); /* now stdout and pdes[1] are equivalent (dup returns lowest free descriptor) */ if((execlp("program1", "program1", "arg1", NULL)) == -1) die("execlp()");_exit(EXIT_SUCCESS); } else { close(0); /* close stdin */ if(dup(pdes[0]) == -1) die("dup()"); if((execlp("program2", "program2", "arg1", NULL)) == -1) die("execlp()");exit(EXIT_SUCCESS); } return 0; } void die(const char *msg) { perror(msg); exit(EXIT_FAILURE); } See also
References1. ^{{cite web|title=dup, dup2|url=http://pubs.opengroup.org/onlinepubs/9699919799/functions/dup.html|website=opengroup.org}}
2 : C POSIX library|System calls |
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