How to check if a line is blank using regex

Question

The pattern you want is something like this in multiline mode:

^\s*$

Explanation:

• ^ is the beginning of string anchor.
• $ is the end of string anchor.
• \s is the whitespace character class.
• * is zero-or-more repetition of.

In multiline mode, ^ and $ also match the beginning and end of the line.

References:

• regular-expressions.info/Anchors, Character Classes, and Repetition.

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A non-regex alternative:

You can also check if a given string line is "blank" (i.e. containing only whitespaces) by trim()-ing it, then checking if the resulting string isEmpty().

In Java, this would be something like this:

if (line.trim().isEmpty()) {
    // line is "blank"
}

The regex solution can also be simplified without anchors (because of how matches is defined in Java) as follows:

if (line.matches("\\s*")) {
    // line is "blank"
}

API references

• String String.trim()
  • Returns a copy of the string, with leading and trailing whitespace omitted.
• boolean String.isEmpty()
  • Returns true if, and only if, length() is 0.
• boolean String.matches(String regex)
  • Tells whether or not this (entire) string matches the given regular expression.

Actually in multiline mode a more correct answer is this:

/((\r\n|\n|\r)$)|(^(\r\n|\n|\r))|^\s*$/gm

The accepted answer: ^\s*$ does not match a scenario when the last line is blank (in multiline mode).

Try this:

^\s*$

The most portable regex would be ^[ \t\n]*$ to match an empty string (note that you would need to replace \t and \n with tab and newline accordingly) and [^ \n\t] to match a non-whitespace string.

Full credit to bchr02 for this answer. However, I had to modify it a bit to catch the scenario for lines that have */ (end of comment) followed by an empty line. The regex was matching the non empty line with */.

New: (^(\r\n|\n|\r)$)|(^(\r\n|\n|\r))|^\s*$/gm

All I did is add ^ as second character to signify the start of line.

Here Blank mean what you are meaning.
A line contains full of whitespaces or a line contains nothing.
If you want to match a line which contains nothing then use '/^$/'.