Problem
You want to determine if a string contains another string, or want to find the position of a string within another string.
Solution
PowerShell provides several options to help you search a string for text.
Use the –like operator to determine whether a string matches a given DOSlike wildcard:
PS >"Hello World" –like "*llo W*"
True Use the –match operator to determine whether a string matches a given regular expression:
PS >"Hello World" –match '.*l[lz]o W.*$' True
Use the Contains() method to determine whether a string contains a specific string:
PS >"Hello World".Contains("World")
True
Use the IndexOf() method to determine the location of one string within another:
PS >"Hello World".IndexOf("World")
6
Discussion
Since PowerShell strings are fully featured .NET objects, they support many stringoriented operations directly. The Contains() and IndexOf() methods are two examples of the many features that the String class supports.
Although they use similar characters, simple wildcards and regular expressions serve significantly different purposes. Wildcards are much more simple than regular expressions, and because of that, more constrained. While you can summarize the rules for wildcards in just four bullet points, entire books have been written to help teach and illuminate the use of regular expressions.
Acommon use of regular expressions is to search for a string that spans multiple lines. By default, regular expressions do not search across lines, but you can use the singleline (?s) option to instruct them
to do so:
PS >"Hello `n World" match "Hello.*World" False PS >"Hello `n World" match "(?s)Hello.*World" True
Wildcards lend themselves to simple matches, while regular expressions lend themselves to more complex matches.
One difficulty sometimes arises when you try to store the result of a PowerShell command in a string, as shown in Example 53.
Example 53. Attempting to store output of a PowerShell command in a string
PS >GetHelp GetChildItem
NAME GetChildItem
SYNOPSIS Gets the items and child items in one or more specified locations.
(...)
PS >$helpContent = GetHelp GetChildItem PS >$helpContent match "location" False
The –match operator searches a string for the pattern you specify but seems to fail in this case. This is because all PowerShell commands generate objects. If you don’t store that output in another variable or pass it to another command, PowerShell converts to a text representation before it displays it to you. In Example 53, $helpContent is a fully featured object, not just its string representation:
PS >$helpContent.Name
GetChildItem
To work with the textbased representation of a PowerShell command, you can explicitly send it through the OutString cmdlet. The OutString cmdlet converts its input into the textbased form you are used to seeing on the screen:
PS >$helpContent = GetHelp GetChildItem | OutString
PS >$helpContent match "location"
True
