New subject: head/sed/tail (was The Unix shell: a 50-year view)

15 Jul 2021

...
 > -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. 
...
  OTOH, this would mean adding more functionality (read:
complexity)
 into the kernel, and there has always been a general desire to avoid
 pushing <stuff> into the kernel when it can be done in userspace.  Do
 you really think using a blocking read(2) is somehow more superior
 than using select(2) to wait for new data to be appended to the file? 
I'm showing my age. tail -f antedated select(2) and was implemented
by alternately sleeping and reading. select(2) indeed overcomes that
clumsiness.

...
  I'll note, with amusement, that -r is one option
which is *NOT* in the
 GNU version of tail.  I see it in FreeBSD, but this looks like a
 BSD'ism. 
-r came from Bell Labs. This reinforces the point that the ancients
had their imperfections.

Doug

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