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Creating a Cmdlet to Access a Data Store

 

This section describes how to create a cmdlet that accesses stored data by way of a Windows PowerShell provider. This type of cmdlet uses the Windows PowerShell provider infrastructure of the Windows PowerShell runtime and, therefore, the cmdlet class must derive from the PSCmdlet base class.

The Select-Str cmdlet described here can locate and select strings in a file or object. The patterns used to identify the string can be specified explicitly through the Path parameter of the cmdlet or implicitly through the Script parameter.

The cmdlet is designed to use any Windows PowerShell provider that derives from IContentCmdletProvider. For example, the cmdlet can specify the FileSystem provider or the Variable provider that is provided by Windows PowerShell. For more information about Windows PowerShell providers, see Designing Your Windows PowerShell provider.

Topics in this section include the following:

The first step in cmdlet creation is always naming the cmdlet and declaring the .NET class that implements the cmdlet. This cmdlet detects certain strings, so the verb name chosen here is "Select", defined by the VerbsCommon class. The noun name "Str" is used because the cmdlet acts upon strings. In the declaration below, note that the cmdlet verb and noun name are reflected in the name of the cmdlet class. For more information about approved cmdlet verbs, see Cmdlet Verb Names.

The .NET class for this cmdlet must derive from the PSCmdlet base class, because it provides the support needed by the Windows PowerShell runtime to expose the Windows PowerShell provider infrastructure. Note that this cmdlet also makes use of the .NET Framework regular expressions classes, such as Regex.

The following code is the class definition for this Select-Str cmdlet.

[Cmdlet(VerbsCommon.Select, "Str", DefaultParameterSetName="PatternParameterSet")]
public class SelectStringCommand : PSCmdlet

This cmdlet defines a default parameter set by adding the DefaultParameterSetName attribute keyword to the class declaration. The default parameter set PatternParameterSet is used when the Script parameter is not specified. For more information about this parameter set, see the Pattern and Script parameter discussion in the following section.

This cmdlet defines several parameters that allow the user to access and examine stored data. These parameters include a Path parameter that indicates the location of the data store, a Pattern parameter that specifies the pattern to be used in the search, and several other parameters that support how the search is performed.

System_CAPS_noteNote

For more information about the basics of defining parameters, see Adding Parameters that Process Command Line Input.

To locate the data store, this cmdlet must use a Windows PowerShell path to identify the Windows PowerShell provider that is designed to access the data store. Therefore, it defines a Path parameter of type string array to indicate the location of the provider.

[Parameter(
           Position = 0,
           ParameterSetName = "ScriptParameterSet",
           Mandatory = true)]                  
[Parameter(
           Position = 0,
           ParameterSetName = "PatternParameterSet",
           ValueFromPipeline = true,
           Mandatory = true)]
           [Alias("PSPath")]
public string[] Path
{
  get { return paths; }
  set { paths = value; }
}
private string[] paths;

Note that this parameter belongs to two different parameter sets and that it has an alias.

Two ParameterAttribute attributes declare that the Path parameter belongs to the ScriptParameterSet and the PatternParameterSet. For more information about parameter sets, see Adding Parameter Sets to a Cmdlet.

The AliasAttribute attribute declares a PSPath alias for the Path parameter. Declaring this alias is strongly recommended for consistency with other cmdlets that access Windows PowerShell providers. For more information about Windows PowerShell paths, see "PowerShell Path Concepts" in How Windows PowerShell Works.

To specify the patterns to search for, this cmdlet declares a Pattern parameter that is an array of strings. A positive result is returned when any of the patterns are found in the data store. Note that these patterns can be compiled into an array of compiled regular expressions or an array of wildcard patterns used for literal searches.

[Parameter(
           Position = 1,
           ParameterSetName = "PatternParameterSet",
           Mandatory = true)]
public string[] Pattern
{
  get { return patterns; }
  set { patterns = value; }
}
private string[] patterns;
private Regex[] regexPattern;
private WildcardPattern[] wildcardPattern;

When this parameter is specified, the cmdlet uses the default parameter set PatternParameterSet. In this case, the cmdlet uses the patterns specified here to select strings. In contrast, the Script parameter could also be used to provide a script that contains the patterns. The Script and Pattern parameters define two separate parameter sets, so they are mutually exclusive.

This cmdlet defines the following support parameters that can be used to modify the search capabilities of the cmdlet.

The Script parameter specifies a script block that can be used to provide an alternate search mechanism for the cmdlet. The script must contain the patterns used for matching and return a PSObject object. Note that this parameter is also the unique parameter that identifies the ScriptParameterSet parameter set. When the Windows PowerShell runtime sees this parameter, it uses only parameters that belong to the ScriptParameterSet parameter set.

[Parameter(
           Position = 1,
           ParameterSetName = "ScriptParameterSet",
           Mandatory = true)]
public ScriptBlock Script
{
  set { script = value; }
  get { return script; }
}
ScriptBlock script;

The SimpleMatch parameter is a switch parameter that indicates whether the cmdlet is to explicitly match the patterns as they are supplied. When the user specifies the parameter at the command line (true), the cmdlet uses the patterns as they are supplied. If the parameter is not specified (false), the cmdlet uses regular expressions. The default for this parameter is false.

[Parameter]
public SwitchParameter SimpleMatch
{
  get { return simpleMatch; }
  set { simpleMatch = value; }
}
private bool simpleMatch;

The CaseSensitive parameter is a switch parameter that indicates whether a case-sensitive search is performed. When the user specifies the parameter at the command line (true), the cmdlet checks for the uppercase and lowercase of characters when comparing patterns. If the parameter is not specified (false), the cmdlet does not distinguish between uppercase and lowercase. For example "MyFile" and "myfile" would both be returned as positive hits. The default for this parameter is false.

[Parameter]
public SwitchParameter CaseSensitive
{
  get { return caseSensitive; }
  set { caseSensitive = value; }
}
private bool caseSensitive;

The Exclude and Include parameters identify items that are explicitly excluded from or included in the search. By default, the cmdlet will search all items in the data store. However, to limit the search performed by the cmdlet, these parameters can be used to explicitly indicate items to be included in the search or omitted.

[Parameter]
public SwitchParameter CaseSensitive
{
  get { return caseSensitive; }
  set { caseSensitive = value; }
}
private bool caseSensitive;
[Parameter]
[ValidateNotNullOrEmpty]
public string[] Include
{
  get
  {
    return includeStrings;
  }
  set
  {
    includeStrings = value;

    this.include = new WildcardPattern[includeStrings.Length];
    for (int i = 0; i < includeStrings.Length; i++)
    {
      this.include[i] = new WildcardPattern(includeStrings[i], WildcardOptions.IgnoreCase);
    }
  }
}

internal string[] includeStrings = null;
internal WildcardPattern[] include = null;

This cmdlet uses two parameter sets (ScriptParameterSet and PatternParameterSet, which is the default) as the names of two parameter sets used in data access. PatternParameterSet is the default parameter set and is used when the Pattern parameter is specified. ScriptParameterSet is used when the user specifies an alternate search mechanism through the Script parameter. For more information about parameter sets, see Adding Parameter Sets to a Cmdlet.

Cmdlets must override one or more of the input processing methods for the PSCmdlet class. For more information about the input processing methods, see Creating Your First Cmdlet.

This cmdlet overrides the BeginProcessing method to build an array of compiled regular expressions at startup. This increases performance during searches that do not use simple matching.

protected override void BeginProcessing()
{
  WriteDebug("Validating patterns.");
  if (patterns != null)
  {
    foreach(string pattern in patterns)
    {
      if (pattern == null)
      ThrowTerminatingError(new ErrorRecord(
                            new ArgumentNullException(
                            "Search pattern cannot be null."),
                            "NullSearchPattern",
                            ErrorCategory.InvalidArgument,
                            pattern)
                            );
    }

    WriteVerbose("Search pattern(s) are valid.");

    // If a simple match is not specified, then
    // compile the regular expressions once.
    if (!simpleMatch)
    {
      WriteDebug("Compiling search regular expressions.");

      RegexOptions regexOptions = RegexOptions.Compiled;
      if (!caseSensitive)
         regexOptions |= RegexOptions.Compiled;
      regexPattern = new Regex[patterns.Length];

      for (int i = 0; i < patterns.Length; i++)
      {
        try
        {
          regexPattern[i] = new Regex(patterns[i], regexOptions);
        }
        catch (ArgumentException ex)
        {
          ThrowTerminatingError(new ErrorRecord(
                        ex,
                        "InvalidRegularExpression",
                        ErrorCategory.InvalidArgument,
                        patterns[i]
                     ));
        }
      } //Loop through patterns to create RegEx objects.

      WriteVerbose("Pattern(s) compiled into regular expressions.");
    }// If not a simple match.

    // If a simple match is specified, then compile the 
    // wildcard patterns once.
    else
    {
      WriteDebug("Compiling search wildcards.");

      WildcardOptions wildcardOptions = WildcardOptions.Compiled;

      if (!caseSensitive)
      {
        wildcardOptions |= WildcardOptions.IgnoreCase;
      }

      wildcardPattern = new WildcardPattern[patterns.Length];
      for (int i = 0; i < patterns.Length; i++)
      {
        wildcardPattern[i] =
                     new WildcardPattern(patterns[i], wildcardOptions);
      }

      WriteVerbose("Pattern(s) compiled into wildcard expressions.");
    }// If match is a simple match.
  }// If valid patterns are available.
}// End of function BeginProcessing().

This cmdlet also overrides the ProcessRecord method to process the string selections that the user makes on the command line. It writes the results of string selection in the form of a custom object by calling a private MatchString method.

protected override void ProcessRecord()
{
  UInt64 lineNumber = 0;
  MatchInfo result;
  ArrayList nonMatches = new ArrayList();

  // Walk the list of paths and search the contents for
  // any of the specified patterns.
  foreach (string psPath in paths)
  {
    // Once the filepaths are expanded, we may have more than one
    // path, so process all referenced paths.
    foreach(PathInfo path in 
            SessionState.Path.GetResolvedPSPathFromPSPath(psPath)
           )
    {
      WriteVerbose("Processing path " + path.Path);

      // Check if the path represens one of the items to be 
      // excluded. If so, continue to next path.
      if (!MeetsIncludeExcludeCriteria(path.ProviderPath))
         continue;

      // Get the content reader for the item(s) at the
      // specified path.
      Collection<IContentReader> readerCollection = null;
      try
      {
        readerCollection =
                    this.InvokeProvider.Content.GetReader(path.Path);
      }
      catch (PSNotSupportedException ex)
      {
        WriteError(new ErrorRecord(ex,
                   "ContentAccessNotSupported",
                    ErrorCategory.NotImplemented,
                    path.Path)
                   );
        return;
      }

      foreach(IContentReader reader in readerCollection)
      {
        // Reset the line number for this path.
        lineNumber = 0;

        // Read in a single block (line in case of a file) 
        // from the object.
        IList items = reader.Read(1);

        // Read and process one block(line) at a time until
        // no more blocks(lines) exist.
        while (items != null && items.Count == 1) 
        {
          // Increment the line number each time a line is
          // processed.
          lineNumber++;

          String message = String.Format("Testing line {0} : {1}",
                                        lineNumber, items[0]);

          WriteDebug(message);

          result = SelectString(items[0]);

          if (result != null)
          {
            result.Path = path.Path;
            result.LineNumber = lineNumber;

            WriteObject(result);
          }
          else
          {
            // Add the block(line) that did notmatch to the 
            // collection of non matches , which will be stored 
            // in the SessionState variable $NonMatches
            nonMatches.Add(items[0]);
          }

          // Get the next line from the object.
          items = reader.Read(1);                  

        }// While loop for reading one line at a time.
      }// Foreach loop for reader collection.
    }// Foreach loop for processing referenced paths.
  }// Foreach loop for walking of path list.

  // Store the list of non-matches in the
  // session state variable $NonMatches.
  try
  {
    this.SessionState.PSVariable.Set("NonMatches", nonMatches);
  }
  catch (SessionStateUnauthorizedAccessException ex)
  {
    WriteError(new ErrorRecord(ex,
               "CannotWriteVariableNonMatches",
               ErrorCategory.InvalidOperation,
               nonMatches)
              );
  }

}// End of protected override void ProcessRecord().

Your cmdlet must open the provider indicated by the Windows PowerShell path so that it can access the data. The SessionState object for the runspace is used for access to the provider, while the InvokeProvider property of the cmdlet is used to open the provider. Access to content is provided by retrieval of the ProviderIntrinsics object for the provider opened.

This sample Select-Str cmdlet uses the Content property to expose the content to scan. It can then call the GetReader method, passing the required Windows PowerShell path.

The following code shows the implementation of this version of this Select-Str cmdlet. Note that this code includes the cmdlet class, private methods used by the cmdlet, and the Windows PowerShell snap-in code used to register the cmdlet. For more information about registering the cmdlet, see Building the Cmdlet.

//
// Copyright (c) 2006 Microsoft Corporation. All rights reserved.
// 
// THIS CODE AND INFORMATION IS PROVIDED "AS IS" WITHOUT WARRANTY OF 
// ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO
// THE IMPLIED WARRANTIES OF MERCHANTABILITY AND/OR FITNESS FOR A 
// PARTICULAR PURPOSE.
//
using System;
using System.Text.RegularExpressions;
using System.Collections;
using System.Collections.ObjectModel;
using System.Management.Automation;
using System.Management.Automation.Provider;
using System.ComponentModel;


namespace Microsoft.Samples.PowerShell.Commands
{
  #region SelectStringCommand
  /// <summary>
  /// This cmdlet searches through PSObjects for particular patterns.
  /// </summary>
  /// <remarks>
  /// This cmdlet can be used to search any object, such as a file or a 
  /// variable, whose provider exposes methods for reading and writing
  /// content.
  /// </remarks>
  [Cmdlet(VerbsCommon.Select, "Str", DefaultParameterSetName="PatternParameterSet")]
  public class SelectStringCommand : PSCmdlet
  {
    #region Parameters
    /// <summary>
    /// Declare a Path parameter that specifies where the data is stored.
    /// This parameter must specify a PowerShell that indicates the 
    /// PowerShell provider that is used to access the objects to be 
    /// searched for matching patterns. This parameter should also have 
    /// a PSPath alias to provide consistancy with other cmdlets that use 
    /// PowerShell providers. 
    /// </summary>
    /// <value>Path of the object(s) to search.</value>
    [Parameter(
               Position = 0,
               ParameterSetName = "ScriptParameterSet",
               Mandatory = true)]                  
    [Parameter(
               Position = 0,
               ParameterSetName = "PatternParameterSet",
               ValueFromPipeline = true,
               Mandatory = true)]
               [Alias("PSPath")]
    public string[] Path
    {
      get { return paths; }
      set { paths = value; }
    }
    private string[] paths;

    /// <summary>
    /// Declare a Pattern parameter that specifies the pattern(s) 
    /// used to find matching patterns in the string representation 
    /// of the objects. A positive result will be returned
    /// if any of the patterns are found in the objects.
    /// </summary>
    /// <remarks>
    /// The patterns will be compiled into an array of wildcard
    /// patterns for a simple match (literal string matching),
    /// or the patterns will be converted into an array of compiled
    /// regular expressions.
    /// </remarks>
    /// <value>Array of patterns to search.</value>
    [Parameter(
               Position = 1,
               ParameterSetName = "PatternParameterSet",
               Mandatory = true)]
    public string[] Pattern
    {
      get { return patterns; }
      set { patterns = value; }
    }
    private string[] patterns;
    private Regex[] regexPattern;
    private WildcardPattern[] wildcardPattern;

    /// <summary>
    /// Declare a Script parameter that specifies a script block 
    /// that is called to perform the matching operations
    /// instead of the matching performed by the cmdlet.
    /// </summary>
    /// <value>Script block that will be called for matching</value>
    [Parameter(
               Position = 1,
               ParameterSetName = "ScriptParameterSet",
               Mandatory = true)]
    public ScriptBlock Script
    {
      set { script = value; }
      get { return script; }
    }
    ScriptBlock script;

    /// <summary> 
    /// Declare a switch parameter that specifies if the pattern(s) are used 
    /// literally. If not (default), searching is 
    /// done using regular expressions.
    /// </summary>
    /// <value>If True, a literal pattern is used.</value> 
    [Parameter]
    public SwitchParameter SimpleMatch
    {
      get { return simpleMatch; }
      set { simpleMatch = value; }
    }
    private bool simpleMatch;

    /// <summary> 
    /// Declare a switch parameter that specifies if a case-sensitive 
    /// search is performed.  If not (default), a case-insensitive search
    /// is perfored.
    /// </summary>
    /// <value>If True, a case-sensitive search is made.</value>
    [Parameter]
    public SwitchParameter CaseSensitive
    {
      get { return caseSensitive; }
      set { caseSensitive = value; }
    }
    private bool caseSensitive;

    /// <summary>
    /// Declare an Include parameter that species which 
    /// specific items are searched.  When this parameter
    /// is used, items that are not listed here are omitted 
    /// from the search.
    /// </summary>
    [Parameter]
    [ValidateNotNullOrEmpty]
    public string[] Include
    {
      get
      {
        return includeStrings;
      }
      set
      {
        includeStrings = value;

        this.include = new WildcardPattern[includeStrings.Length];
        for (int i = 0; i < includeStrings.Length; i++)
        {
          this.include[i] = new WildcardPattern(includeStrings[i], WildcardOptions.IgnoreCase);
        }
      }
    }

    internal string[] includeStrings = null;
    internal WildcardPattern[] include = null;

    /// <summary>
    /// Declare an Exclude parameter that species which 
    /// specific items are omitted from the search.  
    /// </summary> 
    /// 
    [Parameter]
    [ValidateNotNullOrEmpty]
    public string[] Exclude
    {
      get
      {
        return excludeStrings;
      }
      set
      {
        excludeStrings = value;

        this.exclude = new WildcardPattern[excludeStrings.Length];
        for (int i = 0; i < excludeStrings.Length; i++)
        {
          this.exclude[i] = new WildcardPattern(excludeStrings[i], WildcardOptions.IgnoreCase);
        }
      }
    }
    internal string[] excludeStrings;
    internal WildcardPattern[] exclude;

    #endregion Parameters

    #region Overrides
    /// <summary>
    /// If regular expressions are used for pattern matching,
    /// then build an array of compiled regular expressions 
    /// at startup. This increases performance during scanning 
    /// operations when simple matching is not used.
    /// </summary>
    protected override void BeginProcessing()
    {
      WriteDebug("Validating patterns.");
      if (patterns != null)
      {
        foreach(string pattern in patterns)
        {
          if (pattern == null)
          ThrowTerminatingError(new ErrorRecord(
                                new ArgumentNullException(
                                "Search pattern cannot be null."),
                                "NullSearchPattern",
                                ErrorCategory.InvalidArgument,
                                pattern)
                                );
        }

        WriteVerbose("Search pattern(s) are valid.");

        // If a simple match is not specified, then
        // compile the regular expressions once.
        if (!simpleMatch)
        {
          WriteDebug("Compiling search regular expressions.");

          RegexOptions regexOptions = RegexOptions.Compiled;
          if (!caseSensitive)
             regexOptions |= RegexOptions.Compiled;
          regexPattern = new Regex[patterns.Length];

          for (int i = 0; i < patterns.Length; i++)
          {
            try
            {
              regexPattern[i] = new Regex(patterns[i], regexOptions);
            }
            catch (ArgumentException ex)
            {
              ThrowTerminatingError(new ErrorRecord(
                            ex,
                            "InvalidRegularExpression",
                            ErrorCategory.InvalidArgument,
                            patterns[i]
                         ));
            }
          } //Loop through patterns to create RegEx objects.

          WriteVerbose("Pattern(s) compiled into regular expressions.");
        }// If not a simple match.

        // If a simple match is specified, then compile the 
        // wildcard patterns once.
        else
        {
          WriteDebug("Compiling search wildcards.");

          WildcardOptions wildcardOptions = WildcardOptions.Compiled;

          if (!caseSensitive)
          {
            wildcardOptions |= WildcardOptions.IgnoreCase;
          }

          wildcardPattern = new WildcardPattern[patterns.Length];
          for (int i = 0; i < patterns.Length; i++)
          {
            wildcardPattern[i] =
                         new WildcardPattern(patterns[i], wildcardOptions);
          }

          WriteVerbose("Pattern(s) compiled into wildcard expressions.");
        }// If match is a simple match.
      }// If valid patterns are available.
    }// End of function BeginProcessing().


    /// <summary>
    /// Process the input and search for the specified patterns.
    /// </summary> 
    protected override void ProcessRecord()
    {
      UInt64 lineNumber = 0;
      MatchInfo result;
      ArrayList nonMatches = new ArrayList();

      // Walk the list of paths and search the contents for
      // any of the specified patterns.
      foreach (string psPath in paths)
      {
        // Once the filepaths are expanded, we may have more than one
        // path, so process all referenced paths.
        foreach(PathInfo path in 
                SessionState.Path.GetResolvedPSPathFromPSPath(psPath)
               )
        {
          WriteVerbose("Processing path " + path.Path);

          // Check if the path represens one of the items to be 
          // excluded. If so, continue to next path.
          if (!MeetsIncludeExcludeCriteria(path.ProviderPath))
             continue;

          // Get the content reader for the item(s) at the
          // specified path.
          Collection<IContentReader> readerCollection = null;
          try
          {
            readerCollection =
                        this.InvokeProvider.Content.GetReader(path.Path);
          }
          catch (PSNotSupportedException ex)
          {
            WriteError(new ErrorRecord(ex,
                       "ContentAccessNotSupported",
                        ErrorCategory.NotImplemented,
                        path.Path)
                       );
            return;
          }

          foreach(IContentReader reader in readerCollection)
          {
            // Reset the line number for this path.
            lineNumber = 0;

            // Read in a single block (line in case of a file) 
            // from the object.
            IList items = reader.Read(1);

            // Read and process one block(line) at a time until
            // no more blocks(lines) exist.
            while (items != null && items.Count == 1) 
            {
              // Increment the line number each time a line is
              // processed.
              lineNumber++;

              String message = String.Format("Testing line {0} : {1}",
                                            lineNumber, items[0]);

              WriteDebug(message);

              result = SelectString(items[0]);

              if (result != null)
              {
                result.Path = path.Path;
                result.LineNumber = lineNumber;

                WriteObject(result);
              }
              else
              {
                // Add the block(line) that did notmatch to the 
                // collection of non matches , which will be stored 
                // in the SessionState variable $NonMatches
                nonMatches.Add(items[0]);
              }

              // Get the next line from the object.
              items = reader.Read(1);                  

            }// While loop for reading one line at a time.
          }// Foreach loop for reader collection.
        }// Foreach loop for processing referenced paths.
      }// Foreach loop for walking of path list.

      // Store the list of non-matches in the
      // session state variable $NonMatches.
      try
      {
        this.SessionState.PSVariable.Set("NonMatches", nonMatches);
      }
      catch (SessionStateUnauthorizedAccessException ex)
      {
        WriteError(new ErrorRecord(ex,
                   "CannotWriteVariableNonMatches",
                   ErrorCategory.InvalidOperation,
                   nonMatches)
                  );
      }

    }// End of protected override void ProcessRecord().
    #endregion Overrides

    #region PrivateMethods
    /// <summary>
    /// Check for a match using the input string and the pattern(s)
    /// specified.
    /// </summary>
    /// <param name="input">The string to test.</param>
    /// <returns>MatchInfo object containing information about 
    /// result of a match</returns>
    private MatchInfo SelectString(object input)
    {
      string line = null;

      try
      {
        // Convert the object to a string type
        // safely using language support methods
        line = (string)LanguagePrimitives.ConvertTo(
                                                    input,
                                                    typeof(string)
                                                    );
        line = line.Trim(' ','\t');
      }
      catch (PSInvalidCastException ex)
      {
        WriteError(new ErrorRecord(
                   ex,
                   "CannotCastObjectToString",
                   ErrorCategory.InvalidOperation,
                   input)
                   );

        return null;
      }

      MatchInfo result = null;

      // If a scriptblock has been specified, call it 
      // with the path for processing.  It will return
      // one object.
      if (script != null)
      {
        WriteDebug("Executing script block.");

        Collection<PSObject> psObjects =
                             script.Invoke(
                                           line,
                                           simpleMatch,
                                           caseSensitive
                                          );

        foreach (PSObject psObject in psObjects)
        {
          if (LanguagePrimitives.IsTrue(psObject))
          {
            result = new MatchInfo();
            result.Line = line;
            result.IgnoreCase = !caseSensitive;

            break;
          } //End of If.
        } //End ForEach loop.
      } // End of If if script exists.

      // If script block exists, see if this line matches any 
      // of the match patterns.
      else
      {
        int patternIndex = 0;

        while (patternIndex < patterns.Length)
        {
          if ((simpleMatch && 
              wildcardPattern[patternIndex].IsMatch(line))
              || (regexPattern != null 
              && regexPattern[patternIndex].IsMatch(line))
             )
          {
            result = new MatchInfo();
            result.IgnoreCase = !caseSensitive;
            result.Line = line;
            result.Pattern = patterns[patternIndex];

            break;
          }

          patternIndex++;

        }// While loop through patterns.
      }// Else for no script block specified.

      return result;

    }// End of SelectString        

    /// <summary>
    /// Check whether the supplied name meets the include/exclude criteria.
    /// That is - it's on the include list if the include list was 
    /// specified, and not on the exclude list if the explude list was specified.
    /// </summary>
    /// <param name="path">path to validate</param>
    /// <returns>True if the path is acceptable.</returns>
    private bool MeetsIncludeExcludeCriteria(string path)
    {
      bool ok = false;

      // See if the file is on the include list.
      if (this.include != null)
      {
        foreach (WildcardPattern patternItem in this.include)
        {
          if (patternItem.IsMatch(path))
          {
            ok = true;
            break;
          }
        }
      }
      else
      {
        ok = true;
      }

      if (!ok)
         return false;

      // See if the file is on the exclude list.
      if (this.exclude != null)
      {
        foreach (WildcardPattern patternItem in this.exclude)
        {
          if (patternItem.IsMatch(path))
          {
            ok = false;
            break;
          }
        }
      }

      return ok;
    } //MeetsIncludeExcludeCriteria
    #endregion Private Methods

  }// class SelectStringCommand

  #endregion SelectStringCommand

  #region MatchInfo

  /// <summary>
  /// Class representing the result of a pattern/literal match
  /// that is passed through the pipeline by the Select-Str cmdlet.
  /// </summary>
  public class MatchInfo
  {
    /// <summary>
    /// Indicates if the match was done ignoring case.
    /// </summary>
    /// <value>True if case was ignored.</value>
    public bool IgnoreCase
    {
      get { return ignoreCase; }
      set { ignoreCase = value; }
    }
    private bool ignoreCase;

    /// <summary>
    /// Specifies the number of the matching line.
    /// </summary>
    /// <value>The number of the matching line.</value>
    public UInt64 LineNumber
    {
      get { return lineNumber; }
      set { lineNumber = value; }
    }
    private UInt64 lineNumber;

    /// <summary>
    /// Specifies the text of the matching line.
    /// </summary>
    /// <value>The text of the matching line.</value>
    public string Line
    {
      get { return line; }
      set { line = value; }
    }
    private string line;

    /// <summary>
    /// Specifies the full path of the object(file) containing the 
    /// matching line.
    /// </summary>
    /// <remarks>
    /// It will be "inputStream" if the object came from the input 
    /// stream.
    /// </remarks>
    /// <value>The path name</value>
    public string Path
    {
      get { return path; }
      set
      {
        pathSet = true;
        path = value;
      }
    }
    private string path;
    private bool pathSet;

    /// <summary>
    /// Specifies the pattern that was used in the match.
    /// </summary>
    /// <value>The pattern string</value>
    public string Pattern
    {
      get { return pattern; }
      set { pattern = value; }
    }
    private string pattern;

    private const string MatchFormat = "{0}:{1}:{2}";

    /// <summary>
    /// Returns the string representation of this object. The format
    /// depends on whether a path has been set for this object or 
    /// not.
    /// </summary>
    /// <remarks>
    /// If the path component is set, as would be the case when 
    /// matching in a file, ToString() returns the path, line 
    /// number and line text.  If path is not set, then just the 
    /// line text is presented.
    /// </remarks>
    /// <returns>The string representation of the match object.</returns>
    public override string ToString()
    {
      if (pathSet)
         return String.Format(
         System.Threading.Thread.CurrentThread.CurrentCulture,
         MatchFormat,
         this.path,
         this.lineNumber,
         this.line
         );
      else
         return this.line;
    }
  }// End class MatchInfo

  #endregion

  #region PowerShell snap-in

  /// <summary>
  /// Create a PowerShell snap-in for the Select-Str cmdlet.
  /// </summary>
  [RunInstaller(true)]
  public class SelectStringPSSnapIn : PSSnapIn
  {
    /// <summary>
    /// Create an instance of the SelectStrPSSnapin class.
    /// </summary>
    public SelectStringPSSnapIn()
           : base()
    {
    }

    /// <summary>
    /// Specify the name of the PowerShell snap-in.
    /// </summary>
    public override string Name
    {
      get
      {
        return "SelectStrPSSnapIn";
      }
    }

    /// <summary>
    /// Specify the vendor of the PowerShell snap-in.
    /// </summary>
    public override string Vendor
    {
      get
      {
        return "Microsoft";
      }
    }

    /// <summary>
    /// Specify the localization resource information for the vendor. 
    /// Use the format: SnapinName,VendorName.
    /// </summary>
    public override string VendorResource
    {
      get
      {
        return "SelectStrSnapIn,Microsoft";
      }
    }

    /// <summary>
    /// Specifiy the description of the PowerShell snap-in.
    /// </summary>
    public override string Description
    {
      get
        {
          return "This is a PowerShell snap-in for the Select-Str cmdlet.";
        }
    }

    /// <summary>
    /// Specify the localization resource information for the description. 
    /// Use the format: SnapinName,Description. 

    /// </summary>
    public override string DescriptionResource
    {
      get
      {
          return "SelectStrSnapIn,This is a PowerShell snap-in for the Select-Str cmdlet.";
      }
    }
  }
  #endregion PowerShell snap-in


} //namespace Microsoft.Samples.PowerShell.Commands;

After implementing a cmdlet, you must register it with Windows PowerShell through a Windows PowerShell snap-in. For more information about registering cmdlets, see How to Register Cmdlets, Providers, and Host Applications [ps].

When your cmdlet has been registered with Windows PowerShell, you can test it by running it on the command line. The following procedure can be used to test the sample Select-Str cmdlet.

  1. Start Windows PowerShell, and search the Notes file for occurrences of lines with the expression ".NET". Note that the quotation marks around the name of the path are required only if the path consists of more than one word.

    PS> select-str -Path "notes" -Pattern ".NET" -SimpleMatch=$false
    

    The following output appears.

    IgnoreCase   : True
    LineNumber   : 8
    Line         : Because Windows PowerShell works directly with .NET objects, there is often a .NET object
    Path         : C:\PowerShell-Progs\workspace\Samples\SelectStr\notes
    Pattern      : .NET
    IgnoreCase   : True
    LineNumber   : 21
    Line         : You should normally define the class for a cmdlet in a .NET namespace
    Path         : C:\PowerShell-Progs\workspace\Samples\SelectStr\notes
    Pattern      : .NET
    
  2. Search the Notes file for occurrences of lines with the word "over", followed by any other text. The SimpleMatch parameter is using the default value of false. The search is case-insensitive because the CaseSensitive parameter is set to false.

    PS> select-str -Path notes -Pattern "over*" -SimpleMatch -CaseSensitive:$false
    

    The following output appears.

    IgnoreCase   : True
    LineNumber   : 45
    Line         : Override StopProcessing
    Path         : C:\PowerShell-Progs\workspace\Samples\SelectStr\notes
    Pattern      : over*
    IgnoreCase   : True
    LineNumber   : 49
    Line         : overriding the StopProcessing method
    Path         : C:\PowerShell-Progs\workspace\Samples\SelectStr\notes
    Pattern      : over*
    
  3. Search the Notes file using a regular expression as the pattern. The cmdlet searches for alphabetical characters and blank spaces enclosed in parentheses.

    PS> select-str -Path notes -Pattern "\([A-Za-z:blank:]" -SimpleMatch:$false
    

    The following output appears.

    IgnoreCase   : True
    LineNumber   : 1
    Line         : Advisory Guidelines (Consider Following)
    Path         : C:\PowerShell-Progs\workspace\Samples\SelectStr\notes
    Pattern      : \([A-Za-z:blank:]
    IgnoreCase   : True
    LineNumber   : 53
    Line         : If your cmdlet has objects that are not disposed of (written to the pipeline)
    Path         : C:\PowerShell-Progs\workspace\Samples\SelectStr\notes
    Pattern      : \([A-Za-z:blank:]
    
  4. Perform a case-sensitive search of the Notes file for occurrences of the word "Parameter".

    PS> select-str -Path notes -Pattern Parameter -CaseSensitive
    

    The following output appears.

    IgnoreCase   : False
    LineNumber   : 6
    Line         : Support an InputObject Parameter
    Path         : C:\PowerShell-Progs\workspace\Samples\SelectStr\notes
    Pattern      : Parameter
    IgnoreCase   : False
    LineNumber   : 30
    Line         : Support Force Parameter
    Path         : C:\PowerShell-Progs\workspace\Samples\SelectStr\notes
    Pattern      : Parameter
    
  5. Search the variable provider shipped with Windows PowerShell for variables that have numerical values from 0 through 9.

    PS Variable:\> select-str -Path * -Pattern "[0-9]"
    

    The following output appears.

    IgnoreCase   : True
    LineNumber   : 1
    Line         : 64
    Path         : Variable:\MaximumHistoryCount
    Pattern      : [0-9]
    
  6. Use a script block to search the file SelectStrCommandSample.cs for the string "Pos". The cmatch function for the script performs a case-insensitive pattern match.

    PS> select-str -Path "SelectStrCommandSample.cs" -Script { if ($args[0] -cmatch "Pos"){ return $true } return $false }
    

    The following output appears.

    IgnoreCase   : True
    LineNumber   : 37
    Line         :    Position = 0.
    Path         : C:\PowerShell-Progs\workspace\Samples\SelectStr\SelectStrCommandSample.cs
    Pattern      :
    
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