How to combine variables in Perl?

Question

Is there any other way to combine variables in perl? I accidentally wrote the following line of code:

print "$linenumber is: \n" . $linenumber; 

And this led to the conclusion, for example:

 22 is: 22 

I expected:

 $linenumber is: 22 

So, I thought. It should interpret $linenumber in double quotes as a reference to a variable. (how amazing!)

I'm just wondering:. What are the caveats to using this method and can anyone explain how this works?

Answer 1

Variable interpolation occurs when you use double quotes. Therefore, special characters must be escaped. In this case, you need to exit $ :

 print "\$linenumber is: \n" . $linenumber; 

It can be rewritten as:

 print "\$linenumber is: \n$linenumber"; 

To avoid string interpolation, use single quotes:

 print '$linenumber is: ' . "\n$linenumber"; # No need to escape `$` 

Answer 2

I like. = operator method:

 #!/usr/bin/perl use strict; use warnings; my $text .= "... contents ..."; # Append contents to the end of variable $text. $text .= $text; # Append variable $text contents to variable $text contents. print $text; # Prints "... contents ...... contents ..." 

Answer 3

In Perl, any string constructed with double quotes will be interpolated, so any variable will be replaced by its value. Like many other languages, if you need to print $ , you will need to avoid it.

 print "\$linenumber is:\n$linenumber"; 

OR

 print "\$linenumber is:\n" . $linenumber; 

OR

 printf "\$linenumber is:\n%s", $linenumber; 

Scalar interpolation

Answer 4

If you changed the code from

 print "$linenumber is: \n" . $linenumber; 

to

 print '$linenumber is:' . "\n" . $linenumber; 

or

 print '$linenumber is:' . "\n$linenumber"; 

he will print

 $linenumber is: 22 

What I find useful when I want to print the variable name is to use single quotes so that the variables inside are not translated into their value, which makes it easier to read the code.

Answer 5

In formulating this answer, I found this web page that explains the following information:

 ################################################### #Note that when you have double quoted strings, you don't always need to concatenate. Observe this sample: #!/usr/bin/perl $a='Big '; $b='Macs'; print 'I like to eat ' . $a . $b; #This prints out: # I like to eat Big Macs ################################################### #If we had used double quotes, we could have accomplished the same thing like this: #!/usr/bin/perl $a='Big '; $b='Macs'; print "I like to eat $a $b"; #Printing this: # I like to eat Big Macs #without having to use the concatenating operator (.). ################################################### #Remember that single quotes do not interpret, so had you tried that method with single quotes, like this: #!/usr/bin/perl $a='Big '; $b='Macs'; print 'I like to eat $a $b'; #Your result would have been: # I like to eat $a $b #Which don't taste anywhere near as good. 

I thought it would be useful for the community, so I ask about it and answer my own question. Other helpful answers are more than welcome!

Answer 6

you can backslash $ to print it literally.

 print "\$linenumber is: \n" . $linenumber; 

which prints what you expected. You can also use single quotes if you do not want perl to interpolate variable names, but then "\n" will literally interpolate.