Terminal – Why Control-Left and Control-Right Don’t Navigate by Word in Less

input-methodlessterminaluser input

In less's line editing mode, the left and right arrow keys move the cursor backwards and forwards. I was hoping to use these together with the control key to navigate by word, as promised by man less.

       ^LEFTARROW [ ESC-b or ESC-LEFTARROW ]
              (That is, CONTROL and LEFTARROW simultaneously.)  Move the cursor one word to the left.

       ^RIGHTARROW [ ESC-w or ESC-RIGHTARROW ]
              (That is, CONTROL and RIGHTARROW simultaneously.)  Move the cursor one word to the right.

Unfortunately, this seems not to work in my terminal. (Tilix 1.8.3, VTE 0.52, GTK 3.22.30 on Fedora 28). Instead, pressing Control-left prints something I don't recognise. In the example below, I typed alpha beta and then immediately pressed Control-Left. This added ESC[1;5D to the line.

[1]

Is there some misconfiguration going on here? In other applications (e.g. vim) Control-Left and Control-Right navigate by word as intended.

FWIW, Ctrl + left/right arrow keys issue, might be related as might Arrow keys in less

Best Answer

Because you are not using OS/2

I am not kidding.

The OS/2 input handling code in less has a "special key" mapping for the ⎈ Control+← and ⎈ Control+→ chords to its internal SK_CTL_LEFT_ARROW and SK_CTL_RIGHT_ARROW events.

The Unix code simply has no equivalent mapping. It relies upon termcap, and termcap is notoriously deficient in this area.

What is in square brackets in the doco is right, and what is in parentheses is wrong. You'll have to use ⎋ Escape B, ⎋ Escape F, ⎋ Escape ← (sic!), and ⎋ Escape → (sic!) sequences (not chords, note) until someone makes less better. Please file a report.

(In some terminal emulators, you can configure a modifier key to cause an ⎋ Escape to be prefixed. This is not true for all terminal emulators and terminals, in particular the ones whose input control sequences are being emulated here (which, rather, report modifiers in the CSI sequence), and the important part is that the first character received by less from the terminal is ␛. less itself has no notion of such a modifier.)

That is done by screen's sending the escape sequence to turn on the keypad (in termcap ks, terminfo smkx). That happens to turn on the application mode for both the numeric keypad and the cursor keys, because both are present in the ks/smkx capability. screen uses this capability if it is present, when initializing the terminal. screen also follows up by sending the string in the termcap CS capability if it is set, hinting that the original design was to use terminal descriptions where only the keypad was initialized by ks/smkx.

You notice this difference because your key bindings expect the strings sent by the cursor keys in normal mode. If you modified the terminal description for screen to omit the part which changes the cursor keys, you could continue to use those bindings.

For instance, you could do this:

infocmp screen >foo
vi foo

and change the assignment

smkx=\E[?1h\E=,

smkx=\E=,

then

tic foo

to compile the modified description. If you do this as your (non-root) user, tic will put the compiled description in your ~/.terminfo directory. There are drawbacks to this approach, and using tput to obtain key-binding information is preferable. But it is simple.

Debian – Arrow keys in `less`

The manual page, e.g, as you might find on OSX or Unix commands is incomplete:

Among other things, less initializes itself using the termcap strings for the cursor keys, home/page keys, pageup/pagedown keys.
In most configurations, it is also possible to override the termcap settings with environment variables beginning LESS_TERMCAP_, e.g., LESS_TERMCAP_ku to override the ku (cursor-up) string.

Looking at the source code, there's a table cmdtbl in decode.c which gives initial key-bindings, e.g.,

    'k',0,                          A_B_LINE,
    'y',0,                          A_B_LINE,
    CONTROL('Y'),0,                 A_B_LINE,
    SK(SK_CONTROL_K),0,             A_B_LINE,
    CONTROL('P'),0,                 A_B_LINE,
    SK(SK_UP_ARROW),0,              A_B_LINE,

You may be able to see the pattern here: they all go back one line. But I do not see any of that in the manual page.

Terminal – Why Control-Left and Control-Right Don’t Navigate by Word in Less

Best Answer

Because you are not using OS/2

Further reading

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Best Answer

Because you are not using OS/2

Further reading

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