G'day ansh007,

Welcome to the Monastery.

Take a look at "perlop: Range Operators" and the eof function. Your "from line number 100 till end" can be written in Perl as "100 .. eof".

Given this file:

$ cat XXX
A
B
C
D
E
[download]

And an alias I use frequently:

$ alias perle
alias perle='perl -Mstrict -Mwarnings -Mautodie=:all -E'
[download]

You can read from line 3 to the end like this:

$ perle 'open my $fh, "<", "XXX"; while (<$fh>) { print if 3 .. eof }'
C
D
E
[download]

That also works with a literal line number instead of eof. For example, to print lines at the start, or in the middle:

$ perle 'open my $fh, "<", "XXX"; while (<$fh>) { print if 1 .. 3 }'
A
B
C
[download]

$ perle 'open my $fh, "<", "XXX"; while (<$fh>) { print if 2 .. 4 }'
B
C
D
[download]

For those last two, once you've read all the wanted lines, you can exit the while loop early with the last function.

See also: open for a better way to open files; the pragma index for links to strict, warnings and autodie (you should always use the first two; I highly recommend the third for simple I/O error checking); and, if you're unfamiliar with the "-M" and "-E" switches I've used, perlrun.