The use of/dev/null __shell

/dev/null, from the name can be clearly seen as an empty file (write to/dev/null all lost, read/dev/null when you return to EOF), then you will be very puzzled, what is the use of him, please see below to listen to me, perhaps you have seen in a lot of scripts Dev/null, the specific summary of several common uses.
prohibition of standard output. eg: Cat $filename >/dev/null # The file content is lost and will not be exported to standard output.
ii. prohibition of standard errors eg: RM $badname 2>/dev/null #删除文件错误时, there will be no hint to the terminal, have been thrown into the/dev/null
Third, prohibit the standard output and standard error output. EG1: cat $filename 2>/dev/null >/dev/null # if "$filename" does not exist, there will be no error message prompts. # if "$filename" exists, the contents of the file are not printed to standard output. # Therefore, the above code does not output any information at all. # It is useful when you want to test only the exit code of a command without any output. EG2: #-----------The exit begin----------------------of the test command # ls dddd 2>/dev/null 8 echo $?  Output command exit code: 0 for the command to execute correctly, 1-255 for error. #-----------The exit end-----------of the test command # Cat $filename &>/dev/null
Iv. Clear the contents of the log file eg: cat/dev/null >/var/log/messages #: >/var/log/messages has the same effect, but does not produce a new process. (because: is built) cat/dev/null >/var/log/wtmp
v. Hide cookies and no longer be used eg: if [f ~/.netscape/cookies] # if present, delete. then rm-f ~/.netscape/cookies fi ln-s/dev/null ~/.netscape/cookies # Now all cookies will be discarded and not saved on disk.