Thanks a gigaton ! It really was of great help. I will just mention what I have understood.

A backslash removes any special meaning of the symbol succeeding it. If there is no special symbol (like $,\,`,etc.) succeeding it, the backslash is removed.

Code:

 # echo \t
# t

In the following, the special meaning of the succeeding character is removed.

Code:

# set he is a boy
# echo $1
(Here special meaning of $ is retained)
# echo \$1
# $1 (here the special meaning is removed)

Similarly, in

Code:

echo \\\t

the first \ tells that the next slash is to be taken literally (and is itself not printed), so one slash (the second one) is printed. The third slash has no special character after it, so its not printed. The output is :

Code:

# \t

Similarly

Code:

# echo \\\\t
# \\t

. The first and 3rd \ tell that the next \ has to be taken literally, and hence the 2nd and 4th are printed.

As for a backslash within quotes, it has special meaning only when followed by \,$,',",newline. Otherwise, its a simple character.

Code:

# echo "\jao"
# \jao

Here, since \ is not followed by the above mentioned characters, it is treated as a simple character.

Code:

# echo "\\jao"
# \jao

Here, \ is followed by \ (a character in the above list) and so is treated specially (i.e. it makes the following character an ordinary one and is itself removed)

Now, for eval. Eval parses the argument once without executing the command, and then again, this time executing it too.

Code:

# eval echo \\g
# g

On the first parse, the first backslash makes the second \ be treated as an ordinary character, and is itself removed. So, after the first parse, the argument is \g. A similar thing happens in the second parse, and the output is therefore, g.

Code:

# eval echo \\\\g
# \g

Now, in the first parse, what happens is similar to the example I gave a few lines above (the same thing as u type it without eval), and so after the first parse u have : \\g as the argument. Now, in the second pass, the first / makes the next slash appear as an ordinary character, and is itself rmeoved, so we have a single slash followed by g as the answer.

I hope I have understood correctly.