переключение [переназначение] ввода-вывода
In Unix, to send ouput from a process to different file or device or to another process via a pipe, or to have a process read its input from a different file, device or pipe. Some other operating systems have similar facilities. To redirect input to come from a file instead of the keyboard, use "<": myprog < myfile Similarly to redirect output to a file instead of the screen: ls > filelist A pipe redirects the output of one process directly into the input of another who | wc -l A common misuse by beginners is cat myfile | myprog Which is more or less equivalent to "myprog < myfile" except that it introduces an extra unnecessary cat process and buffer space for the pipe. Even the "<" is unnecessary with many standard Unix commands since they accept input file names as command line arguments anyway. Unix's concept of standard input/output and I/O redirection make it easy to combine simple processes in powerful ways and to use the same commands for different purposes.