regex - Cywgin Sed match not working when "/" in string -

testline="this test line: asia/pacific australia" expr="asia\/pacific australia"

this works:

echo "$testline" | sed 's/asia\/pacific australia/test/g'

this not:

echo "$testline" | sed 's/$expr/test/g'

i've tried using multiple "escapes", using different quote marks, using -r , -re sed switches. nothing seems work.

please advise if has working solution. please can advise , provide cygwin output here, many thanks!

first change variable as

expr="asia/pacific australia"

this should work then

echo "$testline" | sed 's_'"$expr"'_test_g'

note sed delimiters can choose other chars well, here _

YU