Help:Parser functions in templates

When applying ParserFunctions to template parameters, a pipe symbol ("|") may be used to provide the empty string as default value, in order to indicate how to handle things if a parameter is or is not passed in.

• {{{1}}}

Sample A

{{#if: {{{1}}} | Parameter 1 is not defined, or is defined and non-null/non-empty. | Parameter 1 is null. It contains only empty string(s) or breaking space(s) etc.}}

Result

{{#if: {{{1}}} | Parameter 1 is not defined, or is defined and non-null/non-empty. | Parameter 1 is null. It contains only empty string(s) or breaking space(s) etc.}}

• {{{1|}}}

Sample B

{{#if: {{{1|}}} | Parameter 1 is defined and non-null/non-empty. | Parameter 1 is not defined, or is defined but null. It contains only empty string(s) or breaking space(s) etc.}}

Result

{{#if: | Parameter 1 is defined and non-null/non-empty. | Parameter 1 is not defined, or is defined but null. It contains only empty string(s) or breaking space(s) etc.}}

Comparison

Condition of parameter 1	Sample A: {{{1}}}	Sample B: {{{1|}}}
not defined	TRUE	FALSE
defined but null/empty	FALSE	FALSE
defined and NOT null/empty	TRUE	TRUE

The second usage ({{{1|}}}) is often the desired way to handle situations where a parameter exists, but is comprised only of empty space.

See also

• Help:Extension:ParserFunctions
• Help:Template