Delete all lines starting with # or ; in Notepad++

Using Notepad++, how do I remove all lines starting with # or ;?

Find:

^[#;].*

Replace with nothing. The ^ indicates the start of a line, the [#;] is a character class to match either # or ;, and .* matches anything else in the line.

In versions of Notepad++ before 6.0, you won't be able to actually remove the lines due to a limitation in its regex engine; the replacement results in blank lines for each line matched. In other words, this:

# foo
; bar
statement;

Will turn into:

statement;

However, the replacement will work in Notepad++ 6.0 if you add \r, \n or \r\n to the end of the pattern, depending on which line ending your file is using, resulting in:

statement;

As others have noted, in Notepad++ 6.0 and later, it is possible to use the "Replace" feature to delete all lines that begin with ";" or "#".

Tao provides a regular expression that serves as a starting point, but it does not account for white-space that may exist before the ";" or "#" character on a given line. For example, lines that begin with ";" or "#" but are "tabbed-in" will not be deleted when using Tao's regular expression, ^(#|;).*\r\n.

Tao's regular expression does not account for the caveat mentioned in BoltClock's answer, either: variances in newline characters across systems.

An improvement is to use ^(\s)*(#|;).*(\r\n|\r|\n)?, which accounts for leading white-space and the newline character variances. Also, the trailing ? handles cases in which the last line of the file begins with # or ;, but does not end with a newline.

For the curious, it is possible to discern which type of newline character is used in a given document (and more than one type may be used): View -> Show Symbol -> Show End of Line.