Answer:

To move to the end of a file in VIM, type

G

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Answer:

If you have opened a port using the ufw command in Ubuntu, but now you want to delete it, you can..

# sudo ufw delete allow 8080/tcp

And then do a reload

# # sudo ufw reload

That's all.

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Answer:

To perform a reverse DNS lookup for a domain in Linux, you can use the dig command, e.g.

# dig -x 8.8.8.8

; <<>> DiG 9.7.0-P1 <<>> -x 8.8.8.8
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 59808
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;8.8.8.8.in-addr.arpa.          IN      PTR

;; ANSWER SECTION:
8.8.8.8.in-addr.arpa.   86328   IN      PTR     google-public-dns-a.google.com.

..

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Answer:

It is easy to use du command to estimate disk usage, however, sometimes you want to ignore some files during the calculation.

To do so, try

# du -h --exclude='*.bak'

The above command will exclude all the file end with the extension .bak during the disk space calculation.

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Answer:

You can simulate a HTTP form post, with a file being uploaded to a remote server using the curl command.

curl -F 'photo=@/upload/image.jpg' http://example.com/upload.php

Assume the name of the form element of your upload is called "photo"

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Answer:

You can use the following command to create an empty png file, using the ImageMagick.

# convert -size 100x100 xc:none empty.png

an empty png of size 100x100 will be created.

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Answer:

If you have a remote file and you can have a quick edit, if you use the following command:

# ssh -t john@remote-server vim /data/test.txt

You will be prompted to login if you don't have proper ssh key in the remote server, and after finishing editing the file, you will quit the ssh session automatically.

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Answer:

Assume you have a text file contains the following content:

1
2
3
10

When you use the sort command to sort them, it will give the following output:

# sort test.txt
1
10
2
3

So you need to sort them according to the numerical values?

Try with the n flag:

# sort -n test.txt
1
2
3
10

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Answer:

To revert the changes of a uncommitted file in Git, you need to use the following command:

# git checkout file

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Answer:

Assume you are copying file using the command below:

# cp foo/bar/test.txt /tmp/

The result is test.txt will be placed inside the folder /tmp/.

In order to let the cp command auto create the foo/bar/ directory structure under /tmp, you can try the command:

# cp --parent foo/bar/test.txt /tmp/

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