Perhaps this is a simple problem, but I've spun my wheels for a couple of hours now --

I want to match pattern in a string, but only if it is not within another pattern. For example, 

$str = 'blfoo and barthisfoothatqux and barsofooquxhim andfoosom foo';

# replace all foo(s) above with 123 except for the ones that are
# surrounded by bar and qux

# note: there are 5 foo(s) in $str above; only 3 should be replaced 
# so $str becomes
# 'bl123 and barthisfoothatqux and barsofooquxhim and123som 123'

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Update: posted clarifications

--

when small people start casting long shadows, it is time to go to bed

In reply to Match a pattern only if it is not within another pattern by punkish

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