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4.9 Counting Characters
This script shows another way to do arithmetic with sed.
In this case we have to add possibly large numbers, so implementing
this by successive increments would not be feasible (and possibly
even more complicated to contrive than this script).
The approach is to map numbers to letters, kind of an abacus
implemented with sed. ‘a’s are units, ‘b’s are
tens and so on: we simply add the number of characters
on the current line as units, and then propagate the carry
to tens, hundreds, and so on.
As usual, running totals are kept in hold space.
On the last line, we convert the abacus form back to decimal.
For the sake of variety, this is done with a loop rather than
with some 80 s commands(9): first we
convert units, removing ‘a’s from the number; then we
rotate letters so that tens become ‘a’s, and so on
until no more letters remain.
#!/usr/bin/sed -nf
# Add n+1 a's to hold space (+1 is for the newline) s/./a/g H x s/\n/a/
# Do the carry. The t's and b's are not necessary, # but they do speed up the thing t a : a; s/aaaaaaaaaa/b/g; t b; b done : b; s/bbbbbbbbbb/c/g; t c; b done : c; s/cccccccccc/d/g; t d; b done : d; s/dddddddddd/e/g; t e; b done : e; s/eeeeeeeeee/f/g; t f; b done : f; s/ffffffffff/g/g; t g; b done : g; s/gggggggggg/h/g; t h; b done : h; s/hhhhhhhhhh//g
: done
$! {
h
b
}
# On the last line, convert back to decimal
: loop /a/! s/[b-h]*/&0/ s/aaaaaaaaa/9/ s/aaaaaaaa/8/ s/aaaaaaa/7/ s/aaaaaa/6/ s/aaaaa/5/ s/aaaa/4/ s/aaa/3/ s/aa/2/ s/a/1/
: next y/bcdefgh/abcdefg/ /[a-h]/ b loop p
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