WhileReadLineWend.vbs<\/B><\/P>Set objFSO = CreateObject(“Scripting.FileSystemObject”)\nSet objFile = objFSO.OpenTextFile(“C:\\fso\\testfile.txt”)<\/p>\nWhile Not objFile.AtEndOfStream\n WScript.Echo objFile.ReadLine\nWend\n<\/PRE>\n
As you probably have already guessed, we have the same kind of construction available to us in Windows PowerShell. Incidentally, the While<\/B> statement in Windows PowerShell works in a very similar manner to the one that you use in VBScript. In the DemoWhileLessThan.ps1<\/B> script, we first initialize the variable $i<\/B> to be equal to 0. We then use the While<\/B> keyword to begin the While<\/B> loop. In Windows PowerShell, we must include the condition that will be evaluated inside a set of parentheses. For this example, we determine the value of the $i<\/B> variable with each pass through the loop. If the value of $i<\/B> is less than the number 5, we will perform the action that is specified inside the braces (curly brackets) that set off the script block. <\/P>\n
In VBScript the condition that is evaluated is positioned on the same line with the While<\/B> statement, but no parentheses are required. Although this is convenient from a typing perspective, it actually makes the code a bit confusing to read. In Windows PowerShell, the statement is outside the parentheses and the condition is clearly delimited by the parentheses. In VBScript the action that is performed is added between two words: while<\/B> and wend<\/B>. In Windows PowerShell, there is no wend<\/B> statement, and the action to be performed is positioned inside a pair of braces. Although shocking at first to users coming from a VBScript background, the braces are always used to contain code. This is what is called a script block, and they are used everywhere. As soon as you are used to seeing them here, you will find them with other language statements too. The good thing is you do not have to look for items such as the keyword Wend<\/B> or the keyword Loop<\/B> (from Do\u2026Loop<\/B> fame).<\/P>\n
In Windows PowerShell, there are two kinds of strings: literal strings and expanding strings. In the DemoWhileLessThan.ps1<\/B> script, we use the expanding string (signified by using the double quotation mark, \u201c<\/B> [the literal string uses the single quotation mark, \u2018<\/B>]). We want to display the name of the variable, and we want to display the value that is contained in the variable. This is a perfect place to showcase the expanding string. In an expanding string, the value that is contained in a variable is displayed on the screen when a line is evaluated. As an example, consider the following code. We assign the value 12 to the variable $i<\/B>. We then put $i<\/B> inside a pair of double quotation marks to make an expanding string. When the line \u201c$i is equal to $i\u201d<\/B> is evaluated, we get \u201c12 is equal to 12\u201d which while true is barely illuminating. This is shown here:<\/P>PS C:\\> $i = 12\nPS C:\\> “$i is equal to $i”\n12 is equal to 12\nPS C:\\>\n<\/PRE>\nWhat we wanted to do is display both the name of the variable and the value that is contained inside it. In VBScript we would have to use concatenation. For this example to work, we have to use the literal string as seenhere: <\/P>
PS C:\\> $i = 12\nPS C:\\> ‘$i is equal to ‘ + $i\n$i is equal to 12\nPS C:\\>\n<\/PRE>\nIf we want to use the advantage of the expanding string, we have to suppress the expanding nature of the expanding string for the first variable. To do this, we use the escape character which is the backtick character. This is seen here:<\/P>
PS C:\\> $i = 12\nPS C:\\> “`$i is equal to $i”\n$i is equal to 12\nPS C:\\>\n<\/PRE>\nIn the DemoWhileLessThan.ps1<\/B> script, we use the expanding string to display our status message of the value of the $i<\/B> variable during each trip through the While<\/B> loop. We suppress the expanding nature of the expanding string for the first $i<\/B> variable so that we can see which variable we are talking about. As soon as we have done this, we increment the value of the $i<\/B> variable by one. To do this, we use the $i++<\/B> syntax. This is identical to saying the following:<\/P>$i = $i + 1<\/PRE>\nThe advantage is that the $i++<\/B> syntax is less typing. The DemoWhileLessThan.ps1<\/B> script is seen here:<\/P>\n
DemoWhileLessThan.ps1<\/B><\/P>$i = 0\nWhile ($i -lt 5)\n {\n “`$i equals $i. This is less than 5”\n $i++ \n } #end while $i lt 5\n<\/PRE>\nWhen you run the DemoWhileLessThan.ps1<\/B> script, you receive the following output:<\/P>$i equals 0. This is less than 5\n$i equals 1. This is less than 5\n$i equals 2. This is less than 5\n$i equals 3. This is less than 5\n$i equals 4. This is less than 5\nPS C:\\>\n<\/PRE>\nNow that you know how to use the While<\/B> loop, let\u2019s examine the WhileReadLine.ps1<\/B> script. The first thing we do is initialize the $i<\/B> variable and set it equal to 0<\/B>. We then use the b cmdlet to read the contents of the T<\/B>estfile.txt<\/B> and to store the contents into the $fileContents<\/B> variable. The Testfile.txt<\/B> file is shown here:<\/P>![\"Image](\"http:\/\/img.microsoft.com\/library\/media\/1033\/technet\/images\/scriptcenter\/qanda\/hsg\/2009\/april\/hey0428\/hsg-04-28-01.jpg\")
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Now we use the While<\/B> statement to loop through the contents of the text file. We do this as long as the value of the $i<\/B> variable is less than or equal to the number of lines in the text file. The number of lines in the text file is represented by the length<\/B> property. Inside the script block, we treat the contents of the $fileContents<\/B> variable as if it is an array (which it is), and we use the $i<\/B> variable to index into the array to print the value of each line in the $fileContents<\/B> variable. We then increment the value of the $i<\/B> variable by one. The WhileReadLine.ps1<\/B> script is shown here:<\/P>\n
WhileReadLine.ps1<\/B><\/P>$i = 0\n$fileContents = Get-Content -path C:\\fso\\testfile.txt\nWhile ( $i -le $fileContents.length )\n {\n $fileContents[$i]\n $i++\n }\n<\/PRE>\nIf you are thinking the WriteReadLine.ps1<\/B> script is a bit difficult, in reality it is about the same difficulty level as the VBScript version. The difference is we resorted to using arrays to work with the content we received from the Get-Content<\/B> cmdlet. The VBScript version uses a FileSystemObject<\/B> and a TextStreamObject<\/B> to work with the data. In reality, we would not have to use a script exactly like the WhileReadLine.ps1<\/B> script to read the contents of the text file. This is because the Get-Content<\/B> cmdlet does this for us automatically. All we really have to do to display the contents of the TestFile.txt<\/B> is use Get-Content<\/B>. This is shown here:<\/P>Get-Content \u2013path c:\\fso\\TestFile.txt<\/PRE>\nThe results of the command are shown here:<\/P>![\"Image](\"http:\/\/img.microsoft.com\/library\/media\/1033\/technet\/images\/scriptcenter\/qanda\/hsg\/2009\/april\/hey0428\/hsg-04-28-02.jpg\")
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By not storing the results of the command in a variable, the contents are automatically displayed. The Get-Content<\/B> command can be further shortened by using the gc<\/B> alias (short name for the Get-Content<\/B> cmdlet) and by omitting the name of the \u2013path<\/B> parameter (which is the default parameter). When we do this, we create a command that resembles the following:<\/P>GC c:\\fso\\TestFile.txt<\/PRE>\nTo find the available aliases for the Get-Content<\/B> cmdlet, I used the Get-Alias<\/B> cmdlet to produce a listing of all the aliases that are defined in the current session. I then pipelined the results of the command to the Where-Object<\/B> and looked for definitions that match Get-Content<\/B>. Here is the command and the output Ireceived:<\/P>PS C:\\> Get-Alias | where-object { $_.definition -eq ‘get-content’}<\/p>\nCommandType Name Definition\n———– —- ———-\nAlias cat Get-Content\nAlias gc Get-Content\nAlias type Get-Content\n<\/PRE>\n
We have shown you that you can use the While<\/B> statement in Windows PowerShell. We have also shown that occasionally you do not have to use the looping behavior because some cmdlets will automatically display information. Finally, we showed you how you can find aliases for cmdlets you frequently use. Join us tomorrow as we continue with Introduction to Windows PowerShell Scripting Week. Until then, take care.<\/P>\n
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Ed Wilson and Craig Liebendorfer, Scripting Guys<\/B><\/P><\/p>\n","protected":false},"excerpt":{"rendered":"
Hey, Scripting Guy! I have been using VBScript for a long time. One of my favorite language statements in VBScript is the While\u2026Wend loop. It is easy to use and easy to understand. Is there an equivalent command in Windows PowerShell?– HS Hi HS, WE never did use the While\u2026Wend loop very much. WE generally […]<\/p>\n","protected":false},"author":595,"featured_media":87096,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[51,3,4,45],"class_list":["post-53873","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-scripting","tag-getting-started","tag-scripting-guy","tag-scripting-techniques","tag-windows-powershell"],"acf":[],"blog_post_summary":"
Hey, Scripting Guy! I have been using VBScript for a long time. One of my favorite language statements in VBScript is the While\u2026Wend loop. It is easy to use and easy to understand. Is there an equivalent command in Windows PowerShell?– HS Hi HS, WE never did use the While\u2026Wend loop very much. WE generally […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/scripting\/wp-json\/wp\/v2\/posts\/53873","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/scripting\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/scripting\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/scripting\/wp-json\/wp\/v2\/users\/595"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/scripting\/wp-json\/wp\/v2\/comments?post=53873"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/scripting\/wp-json\/wp\/v2\/posts\/53873\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/scripting\/wp-json\/wp\/v2\/media\/87096"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/scripting\/wp-json\/wp\/v2\/media?parent=53873"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/scripting\/wp-json\/wp\/v2\/categories?post=53873"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/scripting\/wp-json\/wp\/v2\/tags?post=53873"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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