Tcl Source Code

If you do:
<pre>
   regexp -all {^|\n} "foo\nbar"
</pre>
then it returns <tt>3</tt>. I'd expect that (perhaps) with the <tt>-line</tt> option, but in standard mode that is rather "surprising" as there is only one place where the string starts and only one newline character.

FWIW, I can't reproduce this misbehavior in current Postgres: I get a correct-looking result from

# select regexp_replace(E'foo\nbar', '^|\n', E'\nXX', 'g');
 regexp_replace 
----------------
               +
 XXfoo         +
 XXbar
(1 row)

I speculate that it got fixed as a side-effect of the constraint loop fixes we did awhile ago.
I thought you guys had absorbed those, though.

A consequence of this issue is <a href="https://stackoverflow.com/q/47995488/301832">this</a>:
<pre>
% puts [regsub -all "^|\n" "foo\nbar" "\nXX"]

XXfoo
XX
XXbar
</pre>
The double substitution of <tt>\nXX</tt> before <tt>bar</tt> is again "unexpected".