How To

It’s very easy to check if a file exists with Powershell and take an action if so, here are some examples:

Check if a file exists

$fileToCheck = "C:\tmp\test.txt"
if (Test-Path $fileToCheck -PathType leaf)
{
    #do some stuff
}

Delete file if it exists

$fileToCheck = "C:\tmp\test.txt"
if (Test-Path $fileToCheck -PathType leaf)
{
    Remove-Item $fileToCheck
}

An even shorter method….

$fileToCheck = "c:\tmp\test.txt"
Remove-Item $fileToCheck -ErrorAction Ignore

Check if a file exists and get the content

$fileToCheck = "C:\tmp\test.txt"
if (Test-Path $fileToCheck -PathType leaf) {Get-Content $fileToCheck}

Check if a file exists and print a message if it does or does not exist

$fileToCheck = "C:\tmp\test.txt"
if (Test-Path $fileToCheck -PathType leaf) 
{"File does Exist"}
else
{"File does not exist"}

Check if a file exists and show the properties of the file

$fileToCheck = "C:\tmp\test.txt"
if (Test-Path $fileToCheck -PathType leaf)
{
    $file = Get-Item $fileToCheck
    $file.FullName
    $file.LastAccessTime
    $file.Length
    $file.Extension
    #etc...
}

Check if a file exists and move it to a new location

$fileToCheck = "C:\tmp\test.txt"
$newPath = "c:\tmp\newFolder"
if (Test-Path $fileToCheck -PathType leaf) 
{
    Move-Item -Path $fileToCheck -Destination $newPath
    "$fileToCheck moved to $newPath"
}

It’s obvious from the above examples that Test-Path simply returns a Boolean (i.e. True or False) and executing it on its own will produce exactly that:

The PathType parameter is not strictly required, but it is useful if you want to be sure the check you are performing is actually a file, not a directory.

You can check for a directory by setting PathType to “container”

Unix and Linux have had the incredibly powerful grep tool for decades but windows has always been lacking. PowerShell brings the functionality of grep with the Select-String cmdlet.

Use Select-String to Grep a Single File

To grep a simple text file is as easy as:
Select-String -Path "D:\script\Lorem-Ipsum.txt" -Pattern 'Tachytelic'

You can also use a wildcard:
Select-String -Path "D:\script\*.txt" -Pattern 'Tachytelic'

Grep Recursively with Get-Childitem

Unlike grep, Select-String does not have the ability to search recursively, but you can pipe output to it from Get-ChildItem, like this:
Get-ChildItem -Path "D:\Script\*.txt" -Recurse | Select-String -Pattern 'tachytelic'

Piping to Select-String

Just like grep, you can pipe to Select-String like this:
Get-Content "D:\Script\Lorem-Ipsum.txt" |Select-String "tachytelic"

If you want to make it more like Unix/Linux, add an alias to the Select-String cmdlet:
Set-Alias -Name grep -Value Select-String

Then you can simply pipe to Select-String like this:
cat "D:\Script\Lorem-Ipsum.txt" |grep "tachytelic"

Loop through results from Select-String

Here is an example that greps for a string and uses the results in a loop to determine if some action should be taken:

$pattern = "tachytelic"
$files = Select-String -Path "d:\script\*.txt" -Pattern $pattern
foreach ($file in $files) {
  $filename=$file.Filename
    $item = get-item $file.Path
    "File '{0}' matches the pattern '{1}'" -f $item.FullName, $pattern
    "It was last modified on {0}" -f $item.LastWriteTime
 
  $response = Read-Host -Prompt "Set the archive bit on this file?" 
  If ($response -eq 'Y') {
    $item.attributes="Archive"
    }
}

Which produces output like this:

grepping in Powershell seems to be incredibly fast, I have not conducted any testing against the performance of GNU Grep, but I don’t think you will be disappointed by the performance.