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Changes to grep/src/grep.c
From: |
Charles Levert |
Subject: |
Changes to grep/src/grep.c |
Date: |
Mon, 20 Jun 2005 21:04:39 -0400 |
Index: grep/src/grep.c
diff -u grep/src/grep.c:1.99 grep/src/grep.c:1.100
--- grep/src/grep.c:1.99 Tue Jun 14 20:56:42 2005
+++ grep/src/grep.c Tue Jun 21 01:04:39 2005
@@ -82,8 +82,63 @@
variable GREP_COLOR. The default is to print red. */
static const char *grep_color = "01;31";
-/* Select Graphic Rendition (SGR) strings. */
-/* Also Erase in Line (EL) to Right by default. */
+/* Select Graphic Rendition (SGR, "\33[...m") strings. */
+/* Also Erase in Line (EL) to Right ("\33[K") by default. */
+/* Why have EL to Right after SGR?
+ -- The behavior of line-wrapping when at the bottom of the
+ terminal screen and at the end of the current line is often
+ such that a new line is introduced, entirely cleared with
+ the current background color which may be different from the
+ default one (see the boolean back_color_erase terminfo(5)
+ capability), thus scrolling the display by one line.
+ The end of this new line will stay in this background color
+ even after reverting to the default background color with
+ "\33[m', unless it is explicitly cleared again with "\33[K"
+ (which is the behavior the user would instinctively expect
+ from the whole thing). There may be some unavoidable
+ background-color flicker at the end of this new line because
+ of this (when timing with the monitor's redraw is just right).
+ -- The behavior of HT (tab, "\t") is usually the same as that of
+ Cursor Forward Tabulation (CHT) with a default parameter
+ of 1 ("\33[I"), i.e., it performs pure movement to the next
+ tab stop, without any clearing of either content or screen
+ attributes (including background color); try
+ echo -ne 'asdfqwerzxcv\rASDF\tZXCV\n'
+ in a bash(1) shell to demonstrate this. This is not what the
+ user would instinctively expect of HT (but is ok for CHT).
+ The instinctive behavior would include clearing the terminal
+ cells that are skipped over by HT with blank cells in the
+ current screen attributes, including background color;
+ the boolean dest_tabs_magic_smso terminfo(5) capability
+ indicates this saner behavior for HT, but only some rare
+ terminals have it (although it also indicates a special
+ glitch with standout mode in the Teleray terminal for which
+ it was initially introduced). The remedy is to add "\33K"
+ after each SGR sequence, be it START (to fix the behavior
+ of any HT after that before another SGR) or END (to fix the
+ behavior of an HT in default background color that would
+ follow a line-wrapping at the bottom of the screen in another
+ background color, and to complement doing it after START).
+ Piping grep's output through a pager such as less(1) avoids
+ any HT problems since the pager performs tab expansion.
+
+ Generic disadvantages of this remedy are:
+ -- Some very rare terminals might support SGR but not EL (nobody
+ will use "grep --color" on a terminal that does not support
+ SGR in the first place).
+ -- Having these extra control sequences might somewhat complicate
+ the task of any program trying to parse "grep --color"
+ output in order to extract structuring information from it.
+ A specific disadvantage to doing it after SGR START is:
+ -- Even more possible background color flicker (when timing
+ with the monitor's redraw is just right), even when not at the
+ bottom of the screen.
+ There are no additional disadvantages specific to doing it after
+ SGR END.
+
+ It would be impractical for GNU grep to become a full-fledged
+ terminal program linked against ncurses or the like, so it will
+ not detect terminfo(5) capabilities. */
#define SGR_START "\33[%sm\33[K"
#define SGR_END "\33[m\33[K"
- Changes to grep/src/grep.c, Charles Levert, 2005/06/14
- Changes to grep/src/grep.c,
Charles Levert <=
- Changes to grep/src/grep.c, Charles Levert, 2005/06/20
- Changes to grep/src/grep.c, Charles Levert, 2005/06/21
- Changes to grep/src/grep.c, Charles Levert, 2005/06/21
- Changes to grep/src/grep.c, Charles Levert, 2005/06/21
- Changes to grep/src/grep.c, Charles Levert, 2005/06/21
- Changes to grep/src/grep.c, Charles Levert, 2005/06/21
- Changes to grep/src/grep.c, Charles Levert, 2005/06/21
- Changes to grep/src/grep.c, Charles Levert, 2005/06/21
- Changes to grep/src/grep.c, Charles Levert, 2005/06/21
- Changes to grep/src/grep.c, Charles Levert, 2005/06/21