Select host names from log files - powershell

Question

I have an application that generates 100's of text log files which are like
DaemonReruns=2|
Phase=|
Log=false|
DS=LOG_4|
Schema=LOLYY|
DBMS=mssql|
Host=abc.XYz.com|
IDs=xxxxx,xxxx
I need to select Host from these
I tried
GC C:\log_5.txt |
Select-String -Pattern 'Host=\"([^\"]*)\"'
Gives no results, any help ?

Answer 1

There aren't any quotes in your example input. Try this regex:
get-content C:\log_5.txt | foreach {
if ($_ -match 'Host=([^|]+)') {
$Matches.1
}
}
Note: This actually returns the host names, not just the line.

Answer 2

marsze's helpful answer fixes the problem with your regex and uses a ForEach-Object (foreach) call to extract and return matches via the -match operator and the automatic $Matches variable.
Here's a concise (and better-performing) alternative using the switch statement:
PS> switch -Regex -File C:\log_5.txt { 'Host=([^|]+)' { $Matches[1] } }
abc.XYz.com
Note that -File doesn't accept wildcard-based paths, however, so in order to process multiple file, you'll have to loop over them via Get-ChildItem or Convert-Path.

Answer 3

((Get-Content -Path .\log_5.txt) -match 'Host=') -replace 'Host=',''
returns all the lines starting with Host=

Answer 4

Just for fun ... the super-fast solution:
$regex = [Regex]::new('Host=([^|]+)', 'Compiled, IgnoreCase, CultureInvariant')
& {foreach ($line in [IO.File]::ReadLines("C:\log_5.txt")) {
$m = $regex.Match($line)
if ($m.Success) {
$m.Groups[1].Value
}
}}

Answer 5

If your logs are huge, it could be worth the overhead of Add-Type, and the rest would be much faster:
Add-Type '
using System.IO;
using System.Collections.Generic;
using System.Text.RegularExpressions;
namespace PowerShell
{
public class Tools
{
static Regex regex = new Regex(#"Host=([^|]+)", RegexOptions.Compiled | RegexOptions.IgnoreCase | RegexOptions.CultureInvariant);
public static IEnumerable<string> GetHosts(string path)
{
foreach(var line in File.ReadLines(path))
{
var matches = regex.Match(line);
if (matches.Success)
{
yield return matches.Groups[1].Value;
}
}
}
}
}'
# call this for each log file (very fast)
[PowerShell.Tools]::GetHosts("C:\log_5.txt")

Answer 6

Other answers have the regex side covered well enough. Whenever I see little logs like this I always think about ConvertFrom-StringData which
converts a string that contains one or more key and value pairs into a hash table.
From: help ConvertFrom-StringData
In its basic form we just do something like this:
$pairs = Get-Content -Raw -File $pathtofile | ConvertFrom-StringData
[pscustomobject]$pairs
Which would give you a PowerShell object that you can interact with easily!
DS : LOG_4|
Schema : LOLYY|
IDs : xxxxx,xxxx
Log : false|
DBMS : mssql|
Host : abc.XYz.com|
Phase : |
DaemonReruns : 2|
Doubtful that you need the trailing pipes. You can remove those with some regex or simpler string methods.
[pscustomobject](Get-Content -File $pathToFile | ForEach-Object{$_.trimend("|")} | Out-string | ConvertFrom-StringData)
[pscustomobject]((Get-Content -Raw -File $pathToFile) -replace "(?m)\|$" | ConvertFrom-StringData)
In any case this gives you more options as to how you need to deal with your data.