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 PHP
mb_strrpos
MB_STRRPOS(3) 1 MB_STRRPOS(3)
mb_strrpos - Find position of last occurrence of a string in a string
SYNOPSIS
int mb_strrpos (string $haystack, string $needle, [int $offset], [string $encoding = mb_internal_encoding()])
DESCRIPTION
Performs a multibyte safe strrpos(3) operation based on the number of characters. $needle position is counted from the beginning of
$haystack. First character's position is 0. Second character position is 1.
PARAMETERS
o $haystack
- The string being checked, for the last occurrence of $needle
o $needle
- The string to find in $haystack.
o $offset
- May be specified to begin searching an arbitrary number of characters into the string. Negative values will stop searching at an
arbitrary point prior to the end of the string.
o $encoding
-The $encoding parameter is the character encoding. If it is omitted, the internal character encoding value will be used.
RETURN VALUES
Returns the numeric position of the last occurrence of $needle in the $haystack string. If $needle is not found, it returns FALSE.
CHANGELOG
+--------+---------------------------------------+
|Version | |
| | |
| | Description |
| | |
+--------+---------------------------------------+
| 5.2.0 | |
| | |
| | Added the optional parameter $offset. |
| | |
+--------+---------------------------------------+
NOTES
Note
The $encoding parameter was moved from the third position to the fourth in PHP 5.2.0. For backward compatibility, $encoding can be
specified as the third parameter, but doing so is deprecated and will be removed in the future.
SEE ALSO
mb_strpos(3), mb_internal_encoding(3), strrpos(3).
PHP Documentation Group MB_STRRPOS(3)