Format java properties

Format java properties to a different format. The value which is the string following the first '=' cannot & should not change. All periods in the key get replaced with an underscore "_" and get a prefix of "b_".

Input

# Set a.b
a.b=123
x.y.z=xyz.def
tini=00.x
# Change url to qa
url=http://aabb.com/cache=true
debug.java-options=-Xmx2g
a.b.c.d.e=twenty

Output

# Set a.b
b_a_b=123
b_x_y_z=xyz.def
b_tini=00.x
# Change url to qa
b_url=http://aabb.com/cache=true
b_debug_java-options=-Xmx2g
b_a_b_c_d_e=twenty