Back in my October 4 post,<\/a> I used a Perl construct that I will explain here now: specifically, the eq<\/strong> operator. There is also potential connection between today’s post and my one from October 2<\/a>. <\/p>\n In Perl, you can compare values for equality (using the double equals comparison operator, ==<\/strong>). For example:<\/p>\n #!\/usr\/bin\/perl<\/p>\n $joe=$ARGV[0];<\/p>\n $rob=$ARGV[1];<\/p>\n if($rob==$joe){<\/p>\n print “$rob equals $joe\\n\\n”; else{<\/p>\n print “$rob not equal to $joe\\n\\n”; Let’s imagine test.txt<\/span> is the above program’s name. If it is run from the command line thus:<\/p>\n perl test.txt 4 4<\/span><\/p>\n you’ll likely get the output<\/p>\n 4 equals 4<\/span>.<\/p>\n If, on the other hand, you run it with this command:<\/p>\n perl test.txt 4 5<\/span><\/p>\n you’ll likely receive the response<\/p>\n 5 not equal to 4<\/span><\/p>\n So far, all seems pretty straightforward. However, let’s run the program again, with this command:<\/p>\n perl test.txt coffee tea<\/span><\/p>\n You’ll likely be greeted with the somewhat controversial statement<\/p>\n tea equals coffee<\/span><\/p>\n In Perl, variables that are words (as opposed to numbers) are called strings. A string is written in quotes, such as “coffee”. A string definition might look like<\/p>\n $var1=”coffee”;<\/span><\/p>\n Strings, if defined, have a numerical value of “not zero”. The ==<\/strong> operator is a numerical comparison; from its point of view, “coffee” and “tea” are equal, both being “not zero”.<\/p>\n To compare “coffee” and “tea” as strings, you need to use the operator eq<\/strong> rather than ==<\/strong>, as follows:<\/p>\n if($rob eq $joe)<\/span><\/p>\n If we change the program above, replacing<\/p>\n if($rob == $joe)<\/span><\/p>\n with<\/p>\n if($rob eq $joe)<\/span><\/p>\n it should be able to distinguish between “coffee” and “tea”. If we run it like this:<\/p>\n perl test.txt coffee tea<\/span><\/p>\n We should now receive the reassuring response<\/p>\n tea not equal to coffee<\/span><\/p>\n Various computer languages treat strings and comparisons in possibly different ways. The important point is that a given language might have its own, unexpected way of handling them. Being aware of that possibility, the programmer is better prepared:)<\/p>\n Source:<\/em> Robert’s Perl Tutorial<\/a><\/p>\n
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