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 OPENSOLARIS
shells
shells(4) File Formats shells(4)
NAME
shells - shell database
SYNOPSIS
/etc/shells
DESCRIPTION
The shells file contains a list of the shells on the system. Applications use this file to determine whether a shell is valid. See getuser-
shell(3C). For each shell a single line should be present, consisting of the shell's path, relative to root.
A hash mark (#) indicates the beginning of a comment; subsequent characters up to the end of the line are not interpreted by the routines
which search the file. Blank lines are also ignored.
The following default shells are used by utilities: /bin/bash, /bin/csh, /bin/jsh, /bin/ksh, /bin/ksh93, /bin/pfcsh, /bin/pfksh, /bin/pfsh,
/bin/sh, /bin/tcsh, /bin/zsh, /sbin/jsh, /sbin/sh, /usr/bin/bash, /usr/bin/csh, /usr/bin/jsh, /usr/bin/ksh, /usr/bin/ksh93, /usr/bin/pfcsh,
/usr/bin/pfksh, /usr/bin/pfsh, and /usr/bin/sh, /usr/bin/tcsh, /usr/bin/zsh, and /usr/sfw/bin/zsh. /etc/shells overrides the default list.
Invalid shells in /etc/shells could cause unexpected behavior, such as being unable to log in by way of ftp(1).
FILES
/etc/shells list of shells on system
SEE ALSO
vipw(1B), ftpd(1M), sendmail(1M), getusershell(3C), aliases(4)
SunOS 5.11 20 Nov 2007 shells(4)