BIND 10 trac2968, updated. 8b82620d477ff1eac478407debdef85286f34f79 [2968] Document the sed command

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- Log -----------------------------------------------------------------
commit 8b82620d477ff1eac478407debdef85286f34f79
Author: Mukund Sivaraman <muks at isc.org>
Date:   Mon Jun 10 15:23:51 2013 +0530

    [2968] Document the sed command

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Summary of changes:
 src/bin/dbutil/tests/dbutil_test.sh.in |   15 +++++++++++++++
 1 file changed, 15 insertions(+)

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diff --git a/src/bin/dbutil/tests/dbutil_test.sh.in b/src/bin/dbutil/tests/dbutil_test.sh.in
index 6611b4a..e11c01b 100755
--- a/src/bin/dbutil/tests/dbutil_test.sh.in
+++ b/src/bin/dbutil/tests/dbutil_test.sh.in
@@ -140,6 +140,21 @@ get_schema() {
     db1=@abs_builddir@/dbutil_test_schema_$$
     copy_file $1 $db1
 
+    # The purpose of the following sed command is to join multi-line SQL
+    # statements to form single-line SQL statements.
+    #
+    # The sed command is explained as follows:
+    # ':a' creates a new label "a"
+    # 'N' appends the next line to the pattern space
+    # '$!ba' if it's not the last line, branch to "a"
+    #
+    # The above makes sed loop over the entire sqlite3 output. At this
+    # point, the pattern space contain all lines in the sqlite3 output.
+    #
+    # 's/,[\ ]*\n/, /g' then substitutes lines trailing with comma
+    # followed by zero or more spaces and the newline character, with
+    # just a comma and a single space.
+
     db_schema=`sqlite3 $db1 '.schema' | \
                sed -e ':a' -e 'N' -e '$!ba' -e 's/,[\ ]*\n/, /g' | \
                sort | \