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Perl: The Complete Reference
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Also, because we sometimes want to include a variable name directly within the contents of a string that might otherwise upset Perl s evaluation of that variable name, we can use one of the rules we saw earlier:
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$message = "This is ${name}s computer";
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Any identifier within the braces is interpreted as a string, and because it has a leading $ sign, the ${name} becomes the full name for the variable we are accessing
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The quotes we have already seen in Perl are actually operators they operate on the embedded string In the case of single quotes, this leads to the introduction of a string, and in the case of double quotes, it leads to the introduction of a string that has been evaluated according to the escapes and interpolation rules we have already seen Perl actually supports a number of quoting operators, most of which do more than simply introduce strings Not all of the quoting operators interpolate, and each has a customary form They do, however, share the same basic construction, allowing you to select the quote character that you want to use The full list is given in Table 4-3
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" "" `` () // s/// y/// ""
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q// qq// qx//
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AM FL Y
Meaning
Literal string Literal string Execute external command Quote regular expression
Interpolates
No Yes Yes No Yes Yes No Yes
qw// m// s/// tr/// qr//
Generate word list Regular expression pattern match Regular expression substitution Character translation
Table 4-3
Quoting Mechanisms
4:
Variables and Data
We have already seen examples of the first two mechanisms in Table 4-3 in their customary forms One of the problems with the customary forms is that if you want to embed quotes of the same type (ie single in single), you must escape the quote Using the quote operator, you can circumvent this:
$message = q/Can't send to device/; $text = qq/She said "I can't do this!"/;
FUNDAMENTALS
The character immediately following each operator is the delimiter the delimiter specifies the limits of the construct you are creating You can use any alphanumeric or non-whitespace character (that is, other than space, tab, newline) for a delimiter, but the delimiters must match or complement each other That means that we could use an exclamation mark
$message = q!Can't send to device!;
or we can use a complementary pair of characters such as parentheses, braces, square brackets, or even angle brackets:
$text = qq{She said "I can't do this!"}; $text = qq<She said "I can't do this!">;
Which one you choose will depend entirely on what you are embedding within the construct, and you ll probably find that in most instances you end up using the same delimiting character Also note that the interpolation rules apply according to Table 4-3:
$message = q!Hello $name\n!; $message = qq/Hello $name\n/; # Still outputs Hello $name\n # Outputs Hello Martin with a newline
Interpolation of Array Values
When you embed an array into a string, the elements of the array are included in order separated by the contents of the $ special variable, which by default is a space:
@list = ('hello', 'world'); print "@list\n"; # Outputs 'hello world'
Perl: The Complete Reference
Perl will determine whether the name you have supplied is correct, and it ll raise an error if you ve tried to interpolate an array that doesn t exist This can lead to problems:
print "mc@mcslpcom";
In this instance, Perl is expecting to find an array called @mcslp, and it will obviously fail because we haven t defined such an array Generally, Perl will warn you of this error during compilation and tell you to escape the @ sign:
print "mc\@mcslpcom@;
Here Documents
If you want to introduce multiline strings into your programs, you can use standard quotes:
$string = 'This is a multiline string';
But this is messy and is subject to the same basic laws regarding interpolation and quote usage We could get around it using the q// or qq// operator with different delimiters, but that won t change the underlying issue of delimiter choice and on-screen clarity To get around this, Perl supports here documents these are multiline strings, which interpolate, that continue indefinitely until the multicharacter delimiter that you specify is reached For example:
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