Use of/dev/null in linux, devnull

Use of/dev/null in linux, devnull

Author: iamlaosong

I have a data import program that uses crontab to set scheduled execution. Sometimes, when data needs to be re-imported, it runs once manually. The result shows that the manual import time is longer than the scheduled execution time, the reason is that it is estimated that it is time-consuming because the name and sequence number of the imported data are displayed for each piece of data imported in the program, the output can be redirected to/dev/null. For example:

./Impx. sh>/dev/null

You can regard/dev/null as a "black hole", which is very equivalent to a write-only file, and all the content written to it will be lost forever.

However, if you try to read content from it, nothing can be read. However,/dev/null is very useful for both the command line and script.

1. Disable Standard output

Cat $ filename>/dev/null
# The file content is lost without being output to the standard output.

2. Forbidden standard error

Rm $ badname 2>/dev/null
# The error message [standard error] is thrown to the Pacific Ocean.

3. Disable Standard output and standard error output.

Cat $ filename 2>/dev/null

4. Clear Log File Content

Cat/dev/null>/var/log/messages
#:>/Var/log/messages has the same effect, but no new processes are generated (because: built-in)