filter specific string in php

[xalkar]

\[code\]$var="UseCountry=1UseCountryDefault=1UseState=1UseStateDefault=1UseLocality=1UseLocalityDefault=1cantidad_productos=5expireDays=5apikey=ABQIAAAAFHktBEXrHnX108wOdzd3aBTupK1kJuoJNBHuh0laPBvYXhjzZxR0qkeXcGC_0Dxf4UMhkR7ZNb04dQdistancia=15AutoCoord=1user_add_locality=0SaveContactForm=0ShowVoteRating=0Listlayout=0WidthThumbs=100HeightThumbs=75WidthImage=640HeightImage=480ShowImagesSystem=1ShowOrderBy=0ShowOrderByDefault=0ShowOrderDefault=DESCSimbolPrice=$PositionPrice=0FormatPrice=0ShowLogoAgent=1ShowReferenceInList=1ShowCategoryInList=1ShowTypeInList=1ShowAddressInList=1ShowContactLink=1ShowMapLink=1ShowAddShortListLink=1ShowViewPropertiesAgentLink=1ThumbsInAccordion=5WidthThumbsAccordion=100HeightThumbsAccordion=75ShowFeaturesInList=1ShowAllParentCategory=0AmountPanel=AmountForRegistered=5RegisteredAutoPublish=1AmountForAuthor=5AmountForEditor=5AmountForPublisher=5AmountForManager=5AmountForAdministrator=5AutoPublish=1MailAdminPublish=1DetailLayout=0ActivarTabs=0ActivarDescripcion=1ActivarDetails=1ActivarVideo=1ActivarPanoramica=1ActivarContactar=1ContactMailFormat=1ActivarReservas=1ActivarMapa=1ShowImagesSystemDetail=1WidthThumbsDetail=120HeightThumbsDetail=90idCountryDefault=1idStateDefault=1ms_country=1ms_state=1ms_locality=1ms_category=1ms_Subcategory=1ms_type=1ms_price=1ms_bedrooms=1ms_bathrooms=1ms_parking=1ShowTextSearch=1minprice=maxprice=ms_catradius=1idcatradius1=idcatradius2=ShowTotalResult=1md_country=1md_state=1md_locality=1md_category=1md_type=1showComments=0useComment2=0useComment3=0useComment4=0useComment5=0AmountMonthsCalendar=3StartYearCalendar=2009StartMonthCalendar=1PeriodOnlyWeeks=0PeriodAmount=3PeriodStartDay=1apikey=ABQIAAAAJ879Hg7OSEKVrRKc2YHjixSmyv5A3ewe40XW2YiIN-ybtu7KLRQiVUIEW3WsL8vOtIeTFIVUXDOAcQ";\[/code\]in that string only i want \[code\]"api==ABQIAAAAJ879Hg7OSEKVrRKc2YHjixSmyv5A3ewe40XW2YiIN-ybtu7KLRQiVUIEW3WsL8vOtIeTFIVUXDOAcQ";\[/code\] plz guide me correctly;