Confused about the "onlcr" stty flag

Question

In the stty documentation, the following is mentioned:

[-]icrnl translate carriage return to newline

[-]inlcr translate newline to carriage return

* [-]ocrnl translate carriage return to newline

* [-]onlcr translate newline to carriage return-newline

Notice how the "cr" in icrnl and inlcr and ocrnl mean "carriage return" but it means "carriage return-newline" in onlcr.

Is this a typo, or is this how onlcr really works (i.e. it translates \n to \r\n)?

score 3 · Accepted Answer · edited Jun 11 '20 at 14:16

3

It is not a typo, it is in fact what POSIX also says:

onlcr (-onlcr)

Map (do not map) NL to CR-NL on output. This shall have the effect of setting (not setting) ONLCR in the termios c_oflag field, as defined in XBD General Terminal Interface.

The fact that the mode isn't called "onlcrnl" is probably just to keep the setting names short and consistent (or at least consistently short).

The Rationale section tells us that the standard for stty was adopted from System V, so I'm assuming there was backward compatibility to older systems to care about too.

edited Jun 11 '20 at 14:16

Community

1

answered Oct 30 '17 at 12:12

Kusalananda

333,661

2

And you do want the nl to be translated to crnl so that the terminal takes the cursor back to the beginning of the line (cr) and one line down (nl) – Stéphane Chazelas Oct 30 '17 at 12:44
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The termio flag was already called ONLCR in System III in 1980 – Stéphane Chazelas Oct 30 '17 at 13:03
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Before that (and starting Unix V3 I beleive), stty -nl (CRMOD flag in sgtty.h) would have been the equivalent of today's stty icrnl onlcr – Stéphane Chazelas Oct 30 '17 at 13:21

Confused about the "onlcr" stty flag

1 Answers1