How on earth can zsh know whether it's starting at the beginning of a line or not? Post: 302413434

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Top Forums Programming How on earth can zsh know whether it's starting at the beginning of a line or not? Post 302413434 by AdrienE on Thursday 15th of April 2010 05:03:47 PM

04-15-2010

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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.

AdrienE

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LEARN ABOUT PHP

mb_strrichr

MB_STRRICHR(3)								 1							    MB_STRRICHR(3)

mb_strrichr - Finds the last occurrence of a character in a string within another, case insensitive

SYNOPSIS

       string mb_strrichr (string  $haystack, string  $needle, [bool  $part = false], [string  $encoding = mb_internal_encoding()])

DESCRIPTION

       mb_strrichr(3) finds the last occurrence of $needle in $haystack and returns the portion of $haystack. Unlike mb_strrchr(3), mb_strrichr(3)
       is case-insensitive. If $needle is not found, it returns FALSE.

PARAMETERS

	      o $haystack
		- The string from which to get the last occurrence of $needle

	      o $needle
		- The string to find in $haystack

	      o $part
		- Determines which portion of $haystack this function returns. If set to TRUE, it returns all of $haystack from the  beginning	to
		the last occurrence of $needle. If set to FALSE, it returns all of $haystack from the last occurrence of $needle to the end,

	      o $encoding
		- Character encoding name to use. If it is omitted, internal character encoding is used.

RETURN VALUES

	Returns the portion of $haystack. or FALSE if $needle is not found.

SEE ALSO

       mb_stristr(3), mb_strrchr(3).

PHP Documentation Group 													    MB_STRRICHR(3)

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