No, it will replace $var with the string print "Blah";\n, so when you run it you'll get

print "Blah";
eval print "Blah";
;
[download]

as your output, which is probably not what you want.

See Masem's post and stephen's post below for how to do more interesting interpolation.

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If God had meant us to fly, he would *never* have give us the railroads.
    --Michael Flanders