[TUHS] head/sed/tail (was The Unix shell: a 50-year view)

This somewhat stale note was sent some time ago, but was ignored because it was sent from an unregistered email address. Point well taken. I don't know which of head(1) and sed(1) came first. They appeared in different places at more or less the same time. We in Research declined to adopt head because we already knew the idiom "sed 10q". However one shouldn't have to do related operations in unrelated ways. We finally admitted head in v10. Head was independently invented by Mike Lesk. It was Lesk's program that was deemed superfluous. Head might not have been written if tail didn't exist. But, unlike head, tail strayed from the tao of "do one thing well". Tail -r and tail -f are as cringeworthy as cat -v. -f is a strange feature that effectively turns a regular file into a pipe with memory by polling for new data, A clean general alternative might be to provide an open(2) mode that makes reads at the current file end block if some process has the file open for writing. -r is weird because it enables backwards reading, but only as limited by count. Better would be a program, say revfile, that simply reads backwards by lines. Then tail p has an elegant implementation: revfile p | head | revfile Doug