Format Leading Zeros in PowerShell

I've been working on a question in the forums at ScriptingAnswers.com and the need arose to create a folder name with a 4 digit number. But the number needed to have enough leading zeros so that the number was always 4 digits. For example, Test_0005 or Test_0456. The solution is to use the -f Format operator.

To use this operator on the left side of the statement is a formatting directive and on the right side of the -f operator is the value to be formatted. To get the leading zeros I'm going to use a formatting string like this:

 "{0:0000}"

This basically says, "take a value and make pad it with 4 0s. Here are some examples:

PS C:\> "{0:0000}" -f 4
0004
PS C:\> "{0:0000}" -f 45
0045
PS C:\> "{0:0000}" -f 456
0456
PS C:\> "{0:0000}" -f 4567
4567

Technically, these are string objects, but that's ok. Let's see how we might use this.

PS C:\> 1..10 | foreach {
>>  $i="{0:0000}" -f $_
>>  $dir="c:\test\Target_$i"
>>  $file="file_$i.txt"
>>  $target=Join-Path -Path $dir -ChildPath $file
>>  Write-Host "Updating $target"
>>
>>  }
>>
Updating c:\test\Target_0001\file_0001.txt
Updating c:\test\Target_0002\file_0002.txt
Updating c:\test\Target_0003\file_0003.txt
Updating c:\test\Target_0004\file_0004.txt
Updating c:\test\Target_0005\file_0005.txt
Updating c:\test\Target_0006\file_0006.txt
Updating c:\test\Target_0007\file_0007.txt
Updating c:\test\Target_0008\file_0008.txt
Updating c:\test\Target_0009\file_0009.txt
Updating c:\test\Target_0010\file_0010.txt
PS C:\>

Within the Foreach loop I'm taking the piped in number and formatting to 4 places with leading zeros. This value is then inserted into variables for paths and files, using Join-Path to combine them. This is a much better technique than trying to concatenate.

I hope you find this useful.

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