#!/usr/bin/perl
# this mark # silence a line so it's not executed
# first line #!/usr/bin/perl provides the location of perl executives, so if you don't use "perl first.pl" in commnand line but provide the perl location in script, you can still run use simply "first.pl" to run it. 

print "Hello world\n";
#this is tradition starting from 1972, in first of few C books--start a language with printing hello world. "\n" starts a new line in printing outs. ";" is neccessary for ending a line in scripts.