Input/output redirection
<operating system> 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.
