{"id":8221,"date":"2014-12-01T06:00:00","date_gmt":"2014-12-01T14:00:00","guid":{"rendered":"http:\/\/www.sapien.com\/blog\/?p=8221"},"modified":"2014-11-25T19:01:16","modified_gmt":"2014-11-26T03:01:16","slug":"get-languagekeywords-using-convertfrom-string-on-about-topics","status":"publish","type":"post","link":"https:\/\/dev.sapien.com\/blog\/2014\/12\/01\/get-languagekeywords-using-convertfrom-string-on-about-topics\/","title":{"rendered":"Get-LanguageKeywords: Using ConvertFrom-String on About Topics"},"content":{"rendered":"

There have been some great blog posts about the new ConvertFrom-String<\/strong><\/a> cmdlet in the Windows PowerShell 5.0 preview. My favorite learning tool is an excellent talk by Windows PowerShell MVP Tobias Weltner<\/a> about the full range of text parsing options available in Windows PowerShell 3.0 \u2013 5.0. While learning, I had some fun converting my electric bill and phone bill to PowerShell objects so that I could track them, but I really wasn’t using it for work.<\/p>\n

Until today. <\/p>\n

I wanted to find out whether the new enum<\/strong> keyword in the Windows PowerShell 5.0 preview had been added to the about_language_keywords<\/a> help topic. I ran Update-Help<\/strong><\/a> and then used the Select-String<\/strong><\/a> cmdlet to search for enum<\/strong> keyword. I used the Quiet<\/strong> parameter of Select-String<\/strong>, because I wanted a $True\/$False response.<\/p>\n

Get-Help about_language_keywords | Out-String -Stream | Select-String \"enum\" \u2013Quiet<\/pre>\n
You can use the same Select-String<\/strong> command on the help topic file.<\/p>\n
dir $pshome\\en-us\\about_language_keywords.help.txt | Select-String \u201cenum\u201d -Quiet<\/pre>\n
Both of the commands returned $False<\/strong>, but that’s to be expected, since Windows PowerShell 5.0 is still in preview.<\/p>\n
But, I’d really like to be able to manage those keywords in the same way that I manage type accelerators.<\/p>\n
[PSObject].Assembly.GetType(\u201cSystem.Management.Automation.TypeAccelerators\u201d)::get<\/pre>\n
Or,\u00a0 check for approved verbs:<\/p>\n
Get-Verb<\/pre>\n
In short, I wanted to create a keyword object that I could use in Windows PowerShell. There’s a table in the about_language_keywords help file, but I couldn’t find the contents of that table anywhere else. The About topics are just text files and the table is just a series of text strings, so I looked in my handy toolkit and pulled out ConvertFrom-String<\/strong>.<\/p>\n
Isolate the Keyword Table<\/h2>\n
The brand-new ConvertFrom-String<\/strong> cmdlet takes text strings and returns custom objects (PSCustomObject<\/a>) in which the text strings are values of object properties.<\/p>\n
I tried to create a custom object for each row of the Keyword-Reference table. But when I ran ConvertFrom-String<\/strong> on the entire help topic, I got a very pleasant error message saying that it was too complex and offering to help me with it. In the meantime, I set about isolating the Keyword-Reference table in the help topic.<\/p>\n
\"image\"<\/a><\/p><\/blockquote>\n
I saved the entire about_language_keywords<\/strong> help topic content in the $help<\/span> variable.<\/p>\n
$help = Get-Content $pshome\\en-us\\about_language_keywords.help.txt<\/pre>\n
My first task was to find the line number of the first table entry (Begin…) in the Keyword-Reference table. I could have counted the number of lines from the top of the file or searched for “Begin”, but wanted to make the technique durable \u2013 not dependent on the current version of the file. I decided to search for the Keyword-Reference header.<\/p>\n
I used the Select-String<\/strong> cmdlet and a regular expression to find the Keyword-Reference table header. To get its line number, I used the LineNumber<\/strong> property of the MatchInfo<\/a>object that Select-String returns. The first table entry is two lines after the header, so I added 2 and saved the line number of the first table entry in the $start<\/span> variable.<\/p>\n
$start = (($help | Select-String -Pattern 'Keyword\\s{7,}Reference').LineNumber) + 2<\/pre>\n
Next, I needed the line number of the last table entry, so I looked for the first blank line after the table. (The ^\\s*$<\/strong> is the regular expression for a blank line.) The last table entry is just before the blank line, so I subtracted 1 from the line number, then added the result to the $start<\/span> value to get the line number of the last table entry from the beginning of the file.<\/p>\n
$end = $start + (($help[($start - 1) .. 999] | \r\n    Select-string -Pattern '^\\s*$').LineNumber | \r\n    Select-Object -First 1) - 1<\/pre>\n
With the $start<\/span> and $end<\/span> values, I’ve captured the table in the $table<\/span> variable. (Remember to subtract 1 to convert each line number to an array index.)<\/p>\n
$table = $help[($start \u2013 1)..($end \u2013 1)]<\/pre>\n
\"image\"<\/a><\/p><\/blockquote>\n
Now, the fun begins.<\/p>\n
 <\/p>\n
Create a template<\/h2>\n
The ConvertFrom-String<\/strong> cmdlet takes text strings and returns custom objects (PSCustomObject<\/a>) in which the text strings are values of object properties. I wanted each custom object to have Keyword <\/strong>and Reference<\/strong> properties. The values of those properties are the keyword and reference strings in the table.<\/p>\n
(Remember that Keyword <\/strong>and Reference<\/strong> are just names that I chose. You can use any names for the properties.)<\/p>\n
\r\n        Keyword            Reference\r\n        -----------        -------------------------------------------\r\n\tBegin              about_Functions, about_Functions_Advanced        \r\n        Break              about_Break, about_Trap                          \r\n        Catch              about_Try_Catch_Finally                          \r\n        Continue           about_Continue, about_Trap                       \r\n        Data               about_Data_Sections                              \r\n        Do                 about_Do, about_While<\/pre>\n
 <\/p>\n
The $help<\/span> variables contains text strings, so I needed to tell ConvertFrom-String<\/strong> which parts of each text string go with the Name <\/strong>property, which parts go with the Reference<\/strong> property, and which parts to ignore. To do that, you use a template<\/em><\/strong>, which is a model for the custom objects that you create. The template consists of series of labeled examples that say, in essence, I want it my objects to look like this.<\/p>\n
Let’s begin with the first row of the table.<\/p>\n