perltutorial
root
Well for starters "0" and an empty string("") are false. Anything else is basically true.
<PRE><CODE>
0 # converts to "0" so it's false;
"" # is empty string so it's false;
"0.0" # not "0" or "" so it's true
0.0 # computes to 0 and is then converted to "0" so false
undef # evaluates to "" so it's false -- note, you may get a warning "use of uninitialized value" if you are using -w
2-3+1 # computes to 0 which is converted to "0" so it is false
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