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Changes to grep/doc/grep.texi
From: |
Julian Foad |
Subject: |
Changes to grep/doc/grep.texi |
Date: |
Tue, 08 Nov 2005 14:45:07 -0500 |
Index: grep/doc/grep.texi
diff -u grep/doc/grep.texi:1.56 grep/doc/grep.texi:1.57
--- grep/doc/grep.texi:1.56 Wed Aug 24 07:28:29 2005
+++ grep/doc/grep.texi Tue Nov 8 19:45:05 2005
@@ -1251,22 +1251,24 @@
other greps.
@item
-Why are my expressions whith the vertical bar fail?
+Why is this back-reference failing?
@example
-/bin/echo "ba" | egrep '(a)\1|(b)\1'
+echo 'ba' | egrep '(a)\1|b\1'
@end example
-The first alternate branch fails then the first group was not in the match
-this will make the second alternate branch fails. For example, "aaba" will
-match, the first group participate in the match and can be reuse in the
-second branch.
+This gives no output, because the first alternate @samp{(a)\1} does not match,
+as there is no @samp{aa} in the input, so the @samp{\1} in the second alternate
+has nothing to refer back to, meaning it will never match anything. (The
+second alternate in this example can only match if the first alternate has
+matched -- making the second one superfluous.)
@item
-What do @command{grep, fgrep, egrep} stand for ?
+What do @command{grep, fgrep, egrep} stand for?
-grep comes from the way line editing was done on Unix. For example,
address@hidden uses this syntax to print a list of matching lines on the screen.
+The name @command{grep} comes from the way line editing was done on Unix. For
+example, @command{ed} uses the following syntax to print a list of matching
+lines on the screen:
@example
global/regular expression/print
- Changes to grep/doc/grep.texi,
Julian Foad <=