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sed, a stream editor

4.10 Counting Words

This script is almost the same as the previous one, once each of the words on the line is converted to a single `a' (in the previous script each letter was changed to an `a').

It is interesting that real wc programs have optimized loops for `wc -c', so they are much slower at counting words rather than characters. This script's bottleneck, instead, is arithmetic, and hence the word-counting one is faster (it has to manage smaller numbers).

Again, the common parts are not commented to show the importance of commenting sed scripts.

#!/usr/bin/sed -nf # Convert words to a's s/[ tab][ tab]*/ /g s/^/ / s/ [^ ][^ ]*/a /g s/ //g # Append them to hold space H x s/\n// # From here on it is the same as in wc -c. /aaaaaaaaaa/! bx; s/aaaaaaaaaa/b/g /bbbbbbbbbb/! bx; s/bbbbbbbbbb/c/g /cccccccccc/! bx; s/cccccccccc/d/g /dddddddddd/! bx; s/dddddddddd/e/g /eeeeeeeeee/! bx; s/eeeeeeeeee/f/g /ffffffffff/! bx; s/ffffffffff/g/g /gggggggggg/! bx; s/gggggggggg/h/g s/hhhhhhhhhh//g :x $! { h; b; } :y /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/ y/bcdefgh/abcdefg/ /[a-h]/ by p