search_howto.txt

操作系统文件管理

							1999-01-09
							Emil Brink

			Doing a text search

1. INTRODUCTION
This file describes how to use the Search-command built-into the
internal textviewer in gentoo. The textviewer is the one you see
when you use the ViewText and ViewHex commands, and also when
doing command output capturing.
	The Search command is envoked by clicking the button
labeled "Search..." found close to the bottom right corner of the
textviewer window. As you click it, a dialog window appears that
asks for search parameters.


2. THE SEARCH DIALOG
There are three things you can change in the search parameter
dialog that appears after you click "Search...". These things are:
	1. Search text (RE)
	2. "Ignore Case?"-flag
	3. "Don't Span Newlines?"-flag
These things are further explained in the following secionts:

2.1 The Search Text
Of course, when doing a text search you expect to enter the text
to search for. This is what you do in the entry field in the dialog.
Note that you're not restricted to entering simple text, you can
in fact enter a full regular expression (RE), giving you pretty much
expressive power to be take advantage of.
	For an introduction to regular expressions as they are
used in various places in gentoo, see the "docs/misc.html" file.
	If you're just looking for some old string, and don't
bother about all these RE things, just pretend they're not there,
and enter the string directly. Since any simple string is a RE
that simply matches itself, this works as expected.
	Note that the expression you type in the field will be
remembered and reappear the next time you open the dialog, for
your convenience.

2.2 The "Ignore Case?" Flag
If you want the search to disregard the difference between upper
and lower case of characters, check this box before clicking OK.
	Like the search text itself, the setting of this flag
will be remembered between dialog envokations.

2.3 The "Dont Span Newlines?" Flag
This flag is for advanced searches only, and can typically be
safely ignored (and left in its default OFF state). When active,
it will disallow the regular expression matcher to match the
any-character meta characters (mainly ".") against newline. This
is perhaps not the most useful thing in the world to do, but it
was supported by the regex routines I use, and sounds cool,
so there. :^)


3. PERFORMING THE SEARCH
Once you're satisfied with the settings in the dialog, click the
OK button (or press RETURN) to perform the search. To abandon the
search, click Cancel (or press ESCAPE).
	If the search is successful and something is found, gentoo
will select (highlight) the matching text, and attempt to make the
line(s) containing it visible.

NOTE:	In the current implementation, gentoo will only succeed in
	making the match line visible if there are NO (or very few)
	wrapped lines in the text viewer window. This is silly but
	true.

If the search fails, nothing happens. In particular, there is no
annoying failure-dialog or some such. The only feedback is the
lack of feedback.


4. SEARCH POSITION
The first time you envoke the Search command on a particular text,
the search starts from the first character in the text, as you
might expect.
	The next time you envoke it (on the same text), it will
CONTINUE at the position right after the last in the matched text.
This allows multiple searches for the same thing to be easily
performed "back-to-back", thus covering the entire text.
	If you want to reset the search so that it starts over
from the beginning, click the "Top" button in the text viewer
command button row. This will move the viewer to the top, AND
reset the search so that it again will look at the first character
in the text. The "Bottom" button has the same effect, by the way.


5. MISSING FEATURES
There are several things that are missing from gentoo's text
search command.
	One thing is the ability to search backwards, something
that is commonly found in functions like this. The reason why
this isn't present is simple: the POSIX regex(3) functions that
gentoo uses don't support it. Also, I find I almost never use
it myself. :)
	The handling of search position/continuation is probably
not very intuitive, I will look for a better way to do it.
	There should be some easy way of just repeating the last
search, without having to see the dialog again. Keyboard...
	The "scroll" that attempts to put the matching line in
view doesn't take wrapped lines into account, and thus misses by
far if the window contains wrapped lines. This sucks, but it's
still a lot better than what the GtkText widget itself would do
(which is scroll (slowly!) to the matching line). Whine, nag.
	If you're trying to search the display given by the
built-in ViewHex command, you might expect the Search command to
realize that the data is in hex and adapt. It doesn't, however.
	I'm sure there's more...