How can I use lookbehind in a C# Regex in order to remove line breaks? -

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i have text file repetitve structure header , detail records such as

stopservice:: 697::12::test::20::a@yahoo.com::20 main rd::alcatraz::ca::1200::please send me information a@gmail.com::0::::

i want remove line break between header , detail record process them single record, detail record can contain line breaks need remove line breaks follow directly :: sign.

i'm not pro when using regular expressions searched , tried use approach doesn't work:

 string text = file.readalltext(path);  regex.replace(text, @"(?<=(:))(?!\1):\n", string.empty);  file.writealltext(path, text);

i tried this:

regex.replace(text, @"(?<=::)\n", string.empty);

any idea how can use regex look-behind in case? output should this:

stopservice::697::12::test::20::a@yahoo.com::20 main rd::alcatraz::ca::1200::please send me information     a@gmail.com::0::::

non-regex way

read file line line. check first line , if equal stopservice:: not add newline (environment.newline) after it.

regex way

you can match line break after first :: using (?<=^[^:]*::) look-behind:

var str = "stopservice::\r\n697::12::test::20::a@yahoo.com::20 main rd::alcatraz::ca::1200::please send me information to\r\na@gmail.com::0::::"; var rgx = new regex(@"(?<=^[^:]*::)[\r\n]+"); console.writeline(rgx.replace(str, string.empty));

output:

stopservice::697::12::test::20::a@yahoo.com::20 main rd::alcatraz::ca::1200::please send me information a@gmail.com::0::::

see ideone demo

the look-behind ((?<=...)) matches:

  • ^ - start of string
  • [^:]* - 0 or more characters other :
  • :: - 2 colons

the [\r\n]+ pattern makes sure match newline symbols, if there more one.


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