问题
I'm getting a bunch of text from an outside source, saving it in a variable, and then displaying that variable as part of a larger block of HTML. I need to display it as is, and dollar signs are giving me trouble.
Here's the setup:
# get the incoming text
my $inputText = "This is a $-, as in $100. It is not a 0.";
print <<"OUTPUT";
before-regex: $inputText
OUTPUT
# this regex seems to have no effect
$inputText =~ s/\$/\$/g;
print <<"OUTPUT";
after-regex: $inputText
OUTPUT
In real life, those print blocks are much larger chunks of HTML with variables inserted directly.
I tried escaping the dollar signs using s/\$/\$/g because my understanding is that the first \$ escapes the regex so it searches for $, and the second \$ is what gets inserted and later escapes the Perl so that it just displays $. But I can't get it to work.
Here's what I'm getting:
before-regex: This is a 0, as in . It is not a 0.
after-regex: This is a 0, as in . It is not a 0.
And here's what I want to see:
before-regex: This is a 0, as in . It is not a 0.
after-regex: This is a $-, as in $100. It is not a 0.
Googling brings me to this question. When I try using the array and for loop in the answer, it has no effect.
How can I get the block output to display the variable exactly as it is?
回答1:
When you construct a string with double-quotes, the variable substitution happens immediately. Your string will never contain the $ character in that case. If you want the $ to appear in the string, either use single-quotes or escape it, and be aware that you will not get any variable substitution if you do that.
As for your regex, that is odd. It is looking for $ and replacing them with $. If you want backslashes, you have to escape those too.
回答2:
And here's what I want to see:
before-regex: This is a 0, as in . It is not a 0. after-regex: This is a $-, as in $100. It is not a 0.
hum, well, I'm not sure what the general case is, but maybe the following will do:
s/0/\$-/;
s/in \K/\$100/;
Or did you mean to start with
my $inputText = "This is a \$-, as in \$100. It is not a 0.";
# Produces the string: This is a $-, as in $100. It is not a 0.
or
my $inputText = 'This is a $-, as in $100. It is not a 0.';
# Produces the string: This is a $-, as in $100. It is not a 0.
回答3:
Your mistake is using double quotes instead of single quotes in the declaration of your variable.
This should be :
# get the incoming text
my $inputText = 'This is a $-, as in $100. It is not a 0.';
Learn the difference between ' and " and `. See http://mywiki.wooledge.org/Quotes and http://wiki.bash-hackers.org/syntax/words
This is for shell, but it's the same in Perl.
来源：https://stackoverflow.com/questions/13279138/trouble-escaping-dollar-sign-in-perl