{"id":4251,"date":"2009-04-06T14:56:00","date_gmt":"2009-04-06T14:56:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/powershell\/2009\/04\/06\/checking-for-bound-parameters\/"},"modified":"2019-02-18T13:12:43","modified_gmt":"2019-02-18T20:12:43","slug":"checking-for-bound-parameters","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/powershell\/checking-for-bound-parameters\/","title":{"rendered":"Checking for bound parameters"},"content":{"rendered":"

I recently read an email where someone was asking how they could check in their function if a value had been provided to one of the parameters.  <\/span>Consider for example,<\/font><\/font><\/p>\n

 <\/font><\/p>\n\n\n\n
\n

001
002
003
004
005
006
007
008<\/span><\/p>\n<\/td>\n

\n

function<\/span> <\/span>foo<\/span>
{<\/span>
  <\/span>param<\/span>(<\/span>
    <\/span>$x<\/span>
  )<\/span>
    <\/span>
  <\/span>#If $x was given a value do something, else do something else.<\/span>
}<\/span> <\/span><\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/font><\/p>\n

The usual way I\u2019ve seen people deal this problem is by providing a default value which gets assigned to $x in the case that a value wasn\u2019t provided by the caller and then checking for that value.  <\/span><\/font><\/font><\/p>\n

 <\/font><\/p>\n\n\n\n
\n

001
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005
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007
008<\/span><\/p>\n<\/td>\n

\n

function<\/span> <\/span>foo<\/span>
{<\/span>
  <\/span>param<\/span>(<\/span>
    <\/span>$x<\/span> <\/span>=<\/span> <\/span>$null<\/span>
  )<\/span>
  <\/span>
  <\/span># Check for $x being null.<\/span>
}<\/span> <\/span><\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/font><\/p>\n

That works in the majority of cases, but let\u2019s say that you wanted to differentiate between a default $null value and $null being passed by the caller.  <\/span>What would you do?<\/font><\/font><\/p>\n

If you\u2019re on v2, a simple solution is to look at $PSBoundParameters.  <\/span>It\u2019s a hashtable containing the parameters that were bound and what values were bound to them.  <\/span>Try this:<\/font><\/font><\/p>\n

 <\/font><\/p>\n

 <\/font><\/p>\n\n\n\n
\n

001
002
003
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005
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007
008
009<\/span><\/p>\n<\/td>\n

\n

function<\/span> <\/span>foo<\/span>
{<\/span>
  <\/span>param<\/span>(<\/span>
    <\/span>$x<\/span>,<\/span>
    <\/span>$y<\/span>
  )<\/span>
  <\/span>
  <\/span>$PSBoundParameters<\/span>
}<\/span> <\/span><\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/span><\/p>\n

PS >foo 1<\/span><\/p>\n

 <\/span><\/p>\n

Key                                                                       <\/span>Value<\/span><\/p>\n

—                                                                       <\/span>—–<\/span><\/p>\n

x                                      <\/span>                                       <\/span>1<\/span><\/p>\n

 <\/span><\/p>\n

 <\/span><\/p>\n

PS >foo 1 ‘foo’<\/span><\/p>\n

 <\/span><\/p>\n

Key                                                                       <\/span>Value<\/span><\/p>\n

—                                   <\/span>                                    <\/span>—–<\/span><\/p>\n

x                                                                             <\/span>1<\/span><\/p>\n

y                                                                           <\/span>foo<\/span><\/p>\n

 <\/span><\/p>\n

 <\/span><\/p>\n

 <\/span><\/p>\n

With $PSBoundParameters containing all the bound parameters, to check if a parameter was given a value, it\u2019s a simple matter of checking if $PSBoundParameters contains a key for it.<\/font><\/font><\/p>\n

 <\/font><\/p>\n\n\n\n
\n

001
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\n

<\/p>\n

function<\/span> <\/span>foo<\/span>
{<\/span>
  <\/span>param<\/span>(<\/span>
    <\/span>$x<\/span>
  )<\/span>
  <\/span>
  <\/span>if<\/span> (<\/span>$PSBoundParameters<\/span>.<\/span>ContainsKey(<\/span>‘x’<\/span>))<\/span>
  {<\/span>
    <\/span>write-host<\/span> <\/span>‘X Bound!’<\/span>
  }<\/span>
}<\/span><\/span><\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/span><\/p>\n

 <\/span><\/p>\n

– Marcel Ortiz Soto [MSFT]<\/span><\/font><\/font><\/p>\n

 <\/span><\/p>\n

 <\/span><\/p>\n","protected":false},"excerpt":{"rendered":"

I recently read an email where someone was asking how they could check in their function if a value had been provided to one of the parameters.  Consider for example,   001002003004005006007008 function foo{  param(    $x  )      #If $x was given a value do something, else do something else.}   The usual way I\u2019ve seen people deal this problem is […]<\/p>\n","protected":false},"author":600,"featured_media":13641,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[],"class_list":["post-4251","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-powershell"],"acf":[],"blog_post_summary":"

I recently read an email where someone was asking how they could check in their function if a value had been provided to one of the parameters.  Consider for example,   001002003004005006007008 function foo{  param(    $x  )      #If $x was given a value do something, else do something else.}   The usual way I\u2019ve seen people deal this problem is […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/posts\/4251","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/users\/600"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/comments?post=4251"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/posts\/4251\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/media\/13641"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/media?parent=4251"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/categories?post=4251"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/powershell\/wp-json\/wp\/v2\/tags?post=4251"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}