Redirecting input and output
QNX SDP8.0User's GuideUser
You can override the behavior of commands that read from, or write to,
stdin, stdout, and stderr.
Most commands:
- read their input from the standard input stream (stdin, or file descriptor 0), which is normally assigned to your keyboard
- write their output to the standard output file (stdout, or fd 1), which is normally assigned to your display screen
- write any error messages to the standard error stream (stderr, or fd 2), which is also normally assigned to the screen
Sometimes you want to override this behavior.
| If you want a process to: | Use this symbol: |
|---|---|
| Read from a file, or another device (input redirection) | < |
| Write stdout to a file (output redirection) | > |
| Write stdout to a file, appending to the file's contents (output append) | >> |
For example, the
ls
command lists the files in a directory. If you want to redirect to output of
ls to a file called filelist, enter:
ls > filelist
You can specify a file descriptor for the above
redirections. For example, if you don't want to display any error messages, redirect
stderr to dev/null (a special file, also
known as the bit bucket, that swallows any data written to it and returns end-of-file
when read from):
my_command 2> /dev/null
For more information, see
Input/output redirection
in the entry for ksh in the Utilities Reference.
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