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From: eichin@athena.mit.edu (Mark W. Eichin)
Newsgroups: comp.lang.perl
Subject: re: Splitting by character count in perl?
Message-ID: <1991Mar7.002047.5121@uvaarpa.Virginia.EDU>
Date: 7 Mar 91 00:20:47 GMT
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Reply-To: eichin@athena.mit.edu
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[My apologies for the tutorial style below; I'm writing this for the
reader that doesn't know perl at all, but needs to use it. I welcome
technical corrections publicly, and style comments privately...]
	pack/unpack does exactly what you want. The man page isn't all
that clear on this, though I think the Camel Book has examples which
make it clear... the pack string is almost exactly analogous to the
FORMAT statement in Fortran (or rather, FORTRAN, since I mean the
"classic" versions as opposed to the new standards effort) to the
extent that someone could probably write a translator with little
difficulty.
	As for your particular example, the one-liner:

perl -ne '@two=unpack("a78a*",$_); print "A",$two[0],"\nB",$two[1];'

should do it. Data follows. unpack is taking the current line ($_) and
unpacking it into a string of 78 chars and a string of "thre rest" (*)
and leaving the results into an array called "two" (@two). Then it's
printing the A, the first element of @two ($two[0] - arrays start at
zero, like C, by default, though you can set a variable to adjust
that), then the newline and the B ("\nB"), and then the second element
of two (which *already* contains the trailing newline... $_ is the
*entire* line, and we never did a chop to split off the newline so it
is still there. Using "a78a72" would have also chopped off the
newline, as it is the 151st character...) The -n wraps a loop around
the whole thing, the -e indicates that we're putting the line right
here instead of off in a script.
	I hope this helps; I didn't really want to provide a naked
one-liner, thus the windy explanation. The *important* thing, of
course, is that running the above line, then feeding it the following
three lines of data (78 equals + 72 stars each):

==============================================================================************************************************************************
==============================================================================************************************************************************
==============================================================================************************************************************************

yields:

A==============================================================================
B************************************************************************
A==============================================================================
B************************************************************************
A==============================================================================
B************************************************************************

Hmmm. Double checking your note, you want the A and B *appended* as
well - Ok, fine, I'll leave the above because it makes a point about
newlines, and submit:

perl -ne '@two=unpack("a78a72",$_); print "A",$two[0],"A\nB",$two[1],"B\n";'

A==============================================================================A
B************************************************************************B
A==============================================================================A
B************************************************************************B
A==============================================================================A
B************************************************************************B

Items for further exploration:
	a) the reassembly could be done with pack. 
	b) if the line is less than 150 columns, so will the output. I
suspect the fortran code had the same problem - and that the data
*doesn't* have that problem. See what pack("A78") does, and note how
it would solve that problem.
	c) There is a substr function, but you'd have to use it twice;
would that be slower? [probably, since it would still have to create
the temporary values - but it might be more memory efficient, though
not by enough to matter in this example.]

Enjoy...
				_Mark_ <eichin@athena.mit.edu>
				MIT Student Information Processing Board
				Watchmaker Computing <eichin@watch.com>