04-15-2010
How on earth can zsh know whether it's starting at the beginning of a line or not?
Hi everyone,
I'm currently developing my own shell and I've been wondering how this awesome "printing a reverse-video percent character and a newline when the prompt doesn't start at the beginning of a line" feature is implemented in zsh.
Although it is obvious what is needed to implement this (a way to figure out whether you are at the beginning of a line or not), how to get it is much more complicated. Very weirdly, there seems to exist no way to know the cursor position in a terminal without clearing it and keeping track of the cursor, which a shell obviously cannot do since it can't control the output of the programs it launches (that is why my theory that zsh uses ncurses doesn't seem to hold, although it is very possible that it uses some ncurses functions).
I checked the zsh source code but I'm not used to doing such things, and besides, it's quite like looking for a needle in a haystack (even though I'm fairly confident the code is situated in the zle part)...
I although figured there might be a way to check for the beginning of the line indirectly, I didn't find any yet, so would anyone be able to help me find how zsh does this, or a way to get similar results?
Thanks a lot in advance.
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LEARN ABOUT OPENDARWIN
toe
toe(1M) toe(1M)
NAME
toe - table of (terminfo) entries
SYNOPSIS
toe [-v[n]] [-huUV] file...
DESCRIPTION
With no options, toe lists all available terminal types by primary name with descriptions. File arguments specify the directories to be
scanned; if no such arguments are given, your default terminfo directory is scanned. If you also specify the -h option, a directory header
will be issued as each directory is entered.
There are other options intended for use by terminfo file maintainers:
-u file
says to issue a report on dependencies in the given file. This report condenses the `use' relation: each line consists of the pri-
mary name of a terminal that has use capabilities, followed by a colon, followed by the whitespace-separated primary names of all
terminals which occur in those use capabilities, followed by a newline
-U file
says to issue a report on reverse dependencies in the given file. This report reverses the `use' relation: each line consists of the
primary name of a terminal that occurs in use capabilities, followed by a colon, followed by the whitespace-separated primary names
of all terminals which depend on it, followed by a newline.
-vn specifies that (verbose) output be written to standard error trace information showing toe's progress. The optional integer n is a
number from 1 to 10, interpreted as for tic(1).
-V reports the version of ncurses which was used in this program, and exits.
FILES
/usr/share/terminfo/?/*
Compiled terminal description database.
SEE ALSO
tic(1M), infocmp(1M), captoinfo(1M), infotocap(1M), curses(3X), terminfo(5).
toe(1M)