How can I look up IP addresses for hundreds of hostnames in PowerShell?

For a list this large, PowerShell 7's parallel processing is worth considering. For example:

Get-Content "C:Temphostnames.txt" | ForEach-Object -Parallel {
Resolve-DnsName -Name $_ -Type A -ErrorAction SilentlyContinue
} -ThrottleLimit 50

You would still want to wrap the output in custom objects and export it to CSV, but limiting concurrency helps avoid overwhelming the DNS server.

You can also use the .NET DNS method if you want a simple alternative:

$hostnames = Get-Content "C:Temphostnames.txt"

$results = foreach ($hostname in $hostnames) {
$name = $hostname.Trim()
try {
$ips = [System.Net.Dns]::GetHostAddresses($name) |
ForEach-Object IPAddressToString

[PSCustomObject]@{
HostName = $name
IPAddress = $ips -join '; '
}
}
catch {
[PSCustomObject]@{
HostName = $name
IPAddress = 'Not Found'
}
}
}

$results | Export-Csv "C:Temphostnames_with_ips.csv" -NoTypeInformation

In PowerShell, Resolve-DnsName is usually cleaner than parsing nslookup output because it returns structured objects. Read the hostnames from a text file, resolve the A records, handle failures, and export everything to CSV:

$hostnames = Get-Content "C:Temphosts.txt"

$results = foreach ($hostname in $hostnames) {
$name = $hostname.Trim()
try {
$ips = Resolve-DnsName -Name $name -Type A -ErrorAction Stop |
Where-Object Type -eq 'A' |
Select-Object -ExpandProperty IPAddress

[PSCustomObject]@{
HostName = $name
IPAddress = $ips -join ', '
}
}
catch {
[PSCustomObject]@{
HostName = $name
IPAddress = 'Not Found'
}
}
}

$results | Export-Csv "C:TempHostIPs.csv" -NoTypeInformation