On 20110725_225047, Bob Proulx wrote: > Paul E Condon wrote: > > but 2 are non printing: 0x20 and 0x7F > > I leave the last step as an exercise for the reader. ;-) > > I hate to make this thread longer... Sigh. > > Whether something is printable or not was easier to see in the old > days when printers had dot matrix or daisy wheels or selectric balls > or other such loud and visible print heads. If you emitted a > printable character the head moved forward. If you emited a > non-printable character the head did not move forward. > > Using that definition space is definitely a printable character since > it moves the print head forward. We are all agreed that it is > invisible. But being invisible is not part of the definition of > whether it is printable or not. > > DEL 0x7f is a control character. It is not a printable character. > And its history is interesting. > > You can see this for yourself. > > $ printf "a\x20b\n" | od -tx1 > 0000000 61 20 62 0a > > $ printf "a\x20b\n" > a b > > Space was printed in the above. Space is a printable, if invisible, > character. > > $ printf "a\x7fb\n" | od -tx1 > 0000000 61 7f 62 0a > > $ printf "a\x7fb\n" > ab > > DEL was not printed, did not move the head forward, a was followed > immediately by b, DEL is not a printable character. > > Bob
The original name for DEL was RUBOUT. It was used by telegraphers to rub out a mistaken punch in a paper tapes that they were preparing off line, prior to actual transmission. This is a very practical use and the code with all holes punched was the only one that served this purpose. Also, RUBOUT produced a nice tear strip across the tape. On a teletype, every code caused the print mechanism to cycle, so in a special mechanistic sense, rubout was intended to be "printable." -- Paul E Condon pecon...@mesanetworks.net -- To UNSUBSCRIBE, email to debian-user-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org Archive: http://lists.debian.org/20110726063205.ga19...@cmpq.lan.gnu
