#! /bin/sh
#
# A bug in sed with one-line fix and a workaround.
#
# This demonstrates a bug in sed on Ultrix version 3.0, 4.3-Tahoe,
# Unix-PC (system V) -- probably a lot of versions.
#
# Unix vendors take note -- SUN and NeXT have *already* fixed the bug...
#
# THE BUG:
#
# The bug causes only the odd input lines to be printed in the script below.
#
# According to the manual, the condition for branching with the "t" command
# should be set by successful substitution on the *current* line and cleared
# by either branching or reading a new line.  What appears to happen is that
# the flag is not cleared by reading a new line, so the branch is taken on
# every even numbered line (causing it not to print).
#
# THE WORKAROUND:
#
# Putting an additional "t" command at the end of the script to clear the
# flag is probably the shortest workaround.
#
# THE FIX:
#
# If you have sources, the fix appears to be quite trivial:  the variable
# sflag is set to 1 when a substitute happens, to zero after a TCOM
# happens, but is never set to zero when a new line is read.  A good
# place to do that seems to be where the line number is incremented
# in function gline() just after lnum++.
#
# Corey Satten, corey@cac.washington.edu, 9/28/89.

echo '
    one
    two
    three
    four' | sed -n 's/NeVeR FiNd So DoNt BrAnCh/&/
		    t
		    s/./&/p
		    '