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Functions

Null a file with sudo

Terminal - Null a file with sudo
sudo bash -c "> /var/log/httpd/access_log"
2014-10-02 15:39:47
User: zlemini
Functions: bash sudo
2
Null a file with sudo

Alternatives

There are 3 alternatives - vote for the best!

Terminal - Alternatives
sudo tee /path/to/file < /dev/null

Know a better way?

If you can do better, submit your command here.

What others think

cat /dev/null > /var/log/httpd/access_log

Comment by ethancane 167 weeks and 4 days ago
time for i in {1..1000} ; do bash -c "> /tmp/somefile"; done

real 0m10.800s

user 0m0.032s

sys 0m0.100s

time for i in {1..1000} ; do cat /dev/null >/tmp/somefile; done

real 0m9.932s

user 0m0.040s

sys 0m0.080s

time for i in {1..1000} ; do echo -n > /tmp/somefile ; done

real 0m0.010s

user 0m0.004s

sys 0m0.004s

Comment by pdxdoughnut 167 weeks and 3 days ago

Speed isn't what i was aiming for, just the ability to null a file owned by root etc. - without having to switch to root.

You are running tests without sudo, if you run them with sudo its a lot closer.

Comment by zlemini 167 weeks and 3 days ago

The reason I test for speed is that people who find ideas here often use them in places we didn't think of. Many of those places are inside large for/while loops where a little time really adds up.

And frankly, I was surprised at how big of a difference there was in these two (or three) methods.

Comment by pdxdoughnut 167 weeks ago

This is what you should compare:

time for i in {1..1000} ; do echo -n > /tmp/somefile ; done

real 0m0.053s

user 0m0.027s

sys 0m0.025s

time for i in {1..1000} ; do > /tmp/somefile; done

real 0m0.048s

user 0m0.022s

sys 0m0.025s

But the command is useful to null a file using sudo, if for example /tmp/somefile was owned by root and you wanted to truncate it without switching to root first.

Comment by zlemini 166 weeks and 6 days ago

You are absolutely correct.

Comment by pdxdoughnut 166 weeks and 6 days ago

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Comment by xukaimin 13 weeks and 6 days ago

Your point of view

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