How to escape "-" character at the beginning of filename?

Answer:

Assume you have file named -test.txt, if you want to print it out by the cat command:

# cat -test.txt
cat: invalid option -- '.'
Try `cat --help' for more information.

You will experienced the above error, similar errors will happen with commands such as mv, cp etc.

To correctly handle these kind of files that with file name start with the character -, you need to escape with --

e.g.

#cat -- -test.txt
test

Compare difference of two files side by side

Answer:

To compare the difference of two text files side by side, use the diff command with -y option

E.g.

# diff -y 1.txt 2.txt

a                                                               a
b                                                               b
c                                                               c
                                                              > d

As you can see, the only difference between two files is the character d.