• It seems to me it's not inserting at all. Rather, it replaces.
• You should be using binmode on the handles.
• 1024 is a tiny buffer. I'd use sysread and 64*1024.
• @ARGV is used throughout instead of naming the arguments.
• Globals are needlessly used for the file handles.

Regarding the first point, if you were actually interested in tool that can both insert and replace, I would suggest

cp_range in_file out_file [ in_spec [out_spec] ]

   in_spec: [in_start],[in_length]
       in_start defaults to 0
       in_length defaults to -1 (rest of file)

   out_spec: [out_start],[in_length]
       out_start defaults to end of file
       out_length defaults to -1 (rest of file)

   Negative values for *_start and *_length behave as per substr.
[download]

---

---

Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!

Titles consisting of a single word are discouraged, and in most cases are disallowed outright.

Read Where should I post X? if you're not absolutely sure you're posting in the right place.

Please read these before you post! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

Posts may use any of the Perl Monks Approved HTML tags:

a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr

You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)

	For:		Use:
	&		&
	<		&lt;
	>		&gt;
	[		&#91;
	]		&#93;

Link using PerlMonks shortcuts! What shortcuts can I use for linking?

See Writeup Formatting Tips and other pages linked from there for more info.