Perl - 如何将转义序列放入字符串？

Question

I am converting one form of regex to Perl-compatible regex. I need to replace all occurrences of %s to \\s , so I am doing:

$s =~ s/(?<!%)%s/\s/g;

But it gives me error: Unrecognized escape \\s passed through at .... . Actually I am understanding where the problem is, so probably I can't convert to string some unknown escape sequence. But how do I bypass this thing?

Answer 1

You just need to escape the \\, like:

$s =~ s/(?<!%)%s/\\s/g;

For example

my $s = "this is a %s test with two %s sequences, the last one here %%s not changed";
$s =~ s/(?<!%)%s/\\s/g;
print "$s\n";

prints

this is a \s test with two \s sequences, the last one here %%s not changed

(not sure if you need the %%s to end up being just %s, if so it needs a little tweak or a second regexp to do that).