Regular Expressions 101

Explanation

Pro

^start of line

Group 1([ \t]*\S.*\n)

Character Class[ \t]*

*matches any number of characters from the set below:

the literal (32₁₀ / 40₈ / 20₁₆)

\ta tab character (ASCII 9)

\Sany non-whitespace character

.*any character (except for line terminators), repeated any number of times

\na line-feed (newline) character (ASCII 10)

Character Class[ \t]*

*matches any number of characters from the set below:

the literal (32₁₀ / 40₈ / 20₁₆)

\ta tab character (ASCII 9)

$end of line

\na line-feed (newline) character (ASCII 10)

Positive Lookahead(?=[ \t]*\S)

Character Class[ \t]*

*matches any number of characters from the set below:

the literal (32₁₀ / 40₈ / 20₁₆)

\ta tab character (ASCII 9)

\Sany non-whitespace character

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

Match Information

Detailed match information will be displayed here automatically.

Quick Reference

25 tokens

Regular Expression

^([ \t]*\S.*\n)[ \t]*$\n(?=[ \t]*\S)

New

<nav>

  <ul>

    <li><a href="#">London</a></li>

    <li><a href="#">Paris</a></li>

    <li><a href="#">Tokyo</a></li>

  </ul>

</nav>
 
     
      
 
<div>new context</div>


  
  

<div>new context</div>

Substitution

$1

<nav>

  <ul>

    <li><a href="#">London</a></li>

    <li><a href="#">Paris</a></li>

    <li><a href="#">Tokyo</a></li>

  </ul>

</nav>
 
     
      
 
<div>new context</div>


  
  

<div>new context</div>