Regular Expressions 101

<imgthe literal text <img (case insensitive)

Negative Lookahead(?!.*\s+alt\s*=)

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

\s+any whitespace character, repeated at least once

altthe literal text alt (case insensitive)

\s*any whitespace character, repeated any number of times

=the literal = (61₁₀ / 75₈ / 3D₁₆)

.+any character (except for line terminators), repeated at least once

$end of line

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

i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters

Detailed match information will be displayed here automatically.

Search reference

Regular Expression

<img(?!.*\s+alt\s*=).+$

New

<img src="smiley.gif" alt="Smiley face" height="42" width="42">
<img src="smiley2.gif" height="42" width="42">
<img src="smiley3.gif" alt="Smiley face Three" height="42" width="42">

Regular Expression

Substitution