Thanks a lot bakunin. Honestly I'm not clear about the line of code you've given. Too dumb to understand these awesome little magics That's why I think I couldn't make it work.

1.

Code:

sed '/Pt[ <t>]*\([0-9]\.[0-9]\{14\}[ <t>]*\)\{2\}[0-2]/

In this line

Code:

sed '/Pt[ <t>]*

what's the last "*" for? And for the <t> after Pt, in my input file, the blank spaces after 'Pt' accounts for one <t>+ 2 blank spaces. Is that a problem? I tried with both but didn't work.

2.

Code:

\([0-9]\.[0-9]\{14\}[ <t>]*\)

In continuation of the code, what's the first delimiter "\" for? And does this part mean the x & y coordinates of the line after 'Pt'? When you said
you didn't mean it matches the z coordinate right? At the end there's a tab which I think means the blank space between x & y coordinates, I have 4 blank spaces between coordinates so I tried that.(I tried the <t> too) And also my x and y coordinates can have 1 or 2 digits before decimal point i.e it can be 43.**** or 5.****. So in the code should it be

Code:

\([0-9][0-9]\.[0-9]\{14\}[ <t>]*\)

for accounting the 2 digits before the decimal point?
At the end there's a "*" and a delimiter "\". What do these do?

3.In the last part

Code:

\{2\}[0-2]/ s/$/  bottom!/

Why there's a delimiter "\" at the front? Does this delimiter was introduced to mean there's some blank spaces between y coordinate and the 1st digit of z coordinate i.e 0/2?

4. I understand by the <coordinate> part you meant CODE]\([0-9][0-9]\.[0-9]\{14\}[ <t>]*\)[/CODE] but how does it point to the fact that there two such coordinates (x&y) to get to the first digit of z coordinate(0/2)?

Sorry to give you a hard time man. Again thanks a lot!