Beginning Perl Tutorial - Data Types: Scalars

Single and Double Quoted Strings

From Kirk Brown, former About.com Guide

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A string is a sequence of characters - a bit like a sentence. Strings can be contained within single or double quotes depending on what you're trying to accomplish. When a string is held by single quotes, there are only two special characters to remember: the backslash (\) and the single quote itself ('). For obvious reasons, it would be impossible to use a single quote within a string since it is, in fact, the character that designates the start and end of the string. In order to do so, you must escape the quote using a backslash character, like so:

 $aString = 'It\'s necessary to escape the single quote.';

But then what if you want a backslash at the end of your string? It must be escaped, using itself:

 $aString = 'You must escape the \, but only if it\'s at the end:\\';

So what's the \n character for a newline in the earlier example? Double quotes around your string allows the use of certain special control characters that all begin with the escaping backslash. Characters like \n for a newline or \t for a tab. It also allows your variables (remember $my_name?) to be interpolated, which essentially means replaced with their value in the final output. Of course, with double quotes, the backslash and double quote characters must also be escaped:

 $aString = "It's fine to leave a single quote free.\n A \" and a \\ must be escaped.\n";

So lets modify our two line program above just to see what the output looks like when we use the different quotes:

 #!/usr/local/bin/perl
 $my_name = 'Bobby';
 print "$my_name\n";
 print '$my_name\n';

You should see some output like so:

 $ ./simpleProgram.pl
 Bobby
 $my_name\n$

See how both the $my_name variable and the \n newline are printed literally in the second, single quoted string?

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