Linux Ask! is a Q & A web site specific for Linux related questions. Questions are collected, answered and audited by experienced Linux users.
How to print out a newline character using the echo command?
Answer:
If you try
echo "foo\nbar"
It will print out
foo\nbar
But if you want the two words separate by an actual newline, you can use
echo -e "foo\nbar"
Output would be
foo
bar
You can combine the "-e" flag with other control characters such as "\t", "\r", "\v"... as well.
How to reverse print a file?
Answer:
Normally, you can print a file to standard out by using
cat test.txt
It will show something like:
a
b
c
However, if you want to start from the last line, you can use tac (actually it is reverse of the cat command)
tac test.txt
It will give:
c
b
a
Delete files older than x days in Linux?
Answer:
For example, to delete files under /tmp folder, which were modified more than 6 days, use the command
find /tmp -mtime +5 | xargs rm
How to perform simple calculations in Linux shell?
Answer:
Use the "bc" commad.
echo "101+1" | bc
It will gives:
102
How to check the current logrotate status?
Answer:
logrotate will maintain a status file, normally at the location /var/lib/logrotate/status , you can view the content of this file to see the latest status of all log files managed by logrotate.
Example:
logrotate state -- version 2
"/var/log/apache2/access.log" 2008-12-7
"/var/log/apache2/error.log" 2009-1-25
...
Therefore, it is useful to verify if your desired log files are controlled by logrotate or not.
