正则表达式从x删除到y

Question

I'm new to regex, I know the basics but only the basics. I need to parse a string to remove all occurances of one string to another. For example,

Here is some random text
This wants to stay
foo
This wants to be removed 
bar
And this wants to stay

So the desired output would be

Here is some random text
This wants to stay
And this wants to stay

And removed would be

foo
This wants to be removed
bar

It will always follow the pattern of match 'this string' to 'that string' and remove everything in between, including 'this string' and 'that string'.

The file is a text file, for the sake of this question, the pattern will always start with foo and end with bar, removing foo, bar and everything in between.

Foo and Bar ARE part of the file and need removing.

Answer 1

Regexes are probably the wrong tool here. I'd probably use string equality along with the flip-flop operator.

while (<$input_fh>) {
  print $output_fh unless ($_ eq "foo\n" .. $_ eq "bar\n");
}

You could do it with a regex and a match operator.

while (<$input_fh>) {
  print $output_fh unless /foo/ .. /bar/;
}

That looks neater, but the regexes will match if the strings appear anywhere on an input line.

Update: Inverted the logic on the tests - so it's now correct.

Answer 2

That's not what RegEx is there for. RegEx is there to detect pattern - if you want simple string slice, you should simply iterate over the big string with a simple comparison (or, with other languages which include string operations, indexOf("your string here"); etc. )

However, simple typing of the string would find you the matches: This wants to be removed will return all occurances of that specific string, and thus it is fit for you.

Answer 3

Are you looking for something like this?

#!/usr/bin/perl
$start = "foo";
$end = "bar";
while (<STDIN>) {
$str = $str . $_;
}
$str =~ s/(.*)$start\n.*$end\n(.*)/\1\2/s;
print $str;

The only part of real importance to you is the regex I suppose, but I declare the start and end, then read from standard input and tack each concurrent line onto $str. Then I take str and say "whatever is the first thing within perenthesis before foo put first, whatever is in the second after bar parenthesis put last" (with the backslash \\1 and \\2)

My output from a file containing your lines is:

marshall@marshall-desktop:~$ cat blah | ./haha 
Here is some random text
This wants to stay
And this wants to stay