丢弃的输出(Discard the output)(过滤的输出)

2014/06/01 17:01
阅读数 190

Sometimes you will need to execute a command, but you don't want the output displayed to the screen. In such cases you can discard the output by redirecting it to the file /dev/null:

$ command > /dev/null

Here command is the name of the command you want to execute. The file /dev/null is a special file that automatically discards all its input.

To discard both output of a command and its error output, use standard redirection to redirect STDERR to STDOUT:

$ command > /dev/null 2>&1

Here 2 represents STDERR and 1 represents STDOUT. You can display a message on to STDERR by redirecting STDIN into STDERR as follows:

$ echo message 1>&2

Redirection Commands:

Following is the complete list of commands which you can use for redirection:

Command Description
pgm > file Output of pgm is redirected to file
pgm < file Program pgm reads its input from file.
pgm >> file Output of pgm is appended to file.
n > file Output from stream with descriptor n redirected to file.
n >> file Output from stream with descriptor n appended to file.
n >& m Merge output from stream n with stream m.
n <& m Merge input from stream n with stream m.
<< tag Standard input comes from here through next tag at start of line.
| Takes output from one program, or process, and sends it to another.



                                                                                                                        Name:Xr

                                                                                                                        Date:2014-06-01 17:01


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