Get All Site Collections in a Web Applications using PowerShell

To get all site collections in web application, from SharePoint central Admin, follow these steps:

• Go to SharePoint Central Admin Site >> Application Management 
• Click on "View all site collections" link under Site Collections Group. Select your web application. This page lists all site collections in the selected web application.

Get all site collections in web application using PowerShell:
Here is the PowerShell to list all site collections in web application.

Add-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue

#Set the Web application URL
$WebAppURL="http://intranet.crescent.com"

#Get the Web Application        
$WebApp = Get-SPWebApplication $WebAppURL

#Get all Site collections from the web application
$SitesCollection  = $WebApp.Sites

#Enumerate all site collections in the web application
Foreach($Site in $SitesCollection)
{
    #Get Site Collection URL, Owner, Content Database Details
    Write-host $Site.URL
}

While the above code written in classic manner, you can use PowerShell one-liner to get list of all site collections in web application:

Get-SPWebApplication "http://intranet.crescent.com" | Get-SPSite | Select URL

PowerShell to get all site collections in a web application:
This time, lets use PowerShell expressions to dig into site collection properties, say: Site Name, content database, etc.

Get-SPWebApplication "http://intranet.crescent.com" | Get-SPSite | Select URL,@{Name="Site Name"; Expression={$_.RootWeb.Title}},Owner 

How to get all site collections in a web application and Export to CSV
How about get all site collections in a web application using PowerShell and Export to CSV?

Add-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue

#Web application URL and CSV File location Variables
$WebAppURL="http://intranet.crescent.com"
$CSVFile="C:\SitesList.csv"

#Get list of site collections in a web application powershell
 Get-SPWebApplication $WebAppURL | Get-SPSite | ForEach-Object {
 New-Object -TypeName PSObject -Property @{
             SiteName = $_.RootWeb.Title
             Url = $_.Url
             DatabaseName = $_.ContentDatabase.Name }
} | Export-CSV $CSVFile -NoTypeInformation

This Script gets all site collections from the given web application and exports the site collection data to CSV