5.4 Insert Dynamic Information in a String

Problem

You want to place dynamic information (such as the value of another variable) in a string.

Solution

In an expanding string, include the name of a variable in the string to insert the value of that variable:

PS > $header = "Report for Today"
PS > $myString = "$header`n----------------"
PS > $myString
Report for Today
----------------

To include information more complex than just the value of a variable, enclose it in a subexpression:

PS > $header = "Report for Today"
PS > $myString = "$header`n$('-' * $header.Length)"
PS > $myString
Report for Today
----------------

Discussion

Variable substitution in an expanding string is a simple enough concept, but subexpressions deserve a little clarification.

A subexpression is the dollar sign character, followed by a PowerShell command (or set of commands) contained in parentheses:

$(subexpression)

When PowerShell sees a subexpression in an expanding string, it evaluates the subexpression and places the result in the expanding string. In the Solution, the expression '-' * $header.Length tells PowerShell to make a line of dashes $header.Length long.

Another way to place dynamic information inside a string is to use PowerShell’s string formatting operator, which uses the same rules that .NET string formatting does:

PS > $header = "Report for Today"
PS > $myString = "{0}`n{1}" -f $header,('-' * $header.Length)
PS > $myString
Report for Today
----------------

For an explanation of PowerShell’s formatting operator, see Recipe 5.6. For more information about PowerShell’s escape characters, type Get-Help about_Special_Characters.

See Also

Recipe 5.6, “Place Formatted Information in a String”