More on Temporary Files

This is an expansion of my previous article about creating temporary files in PowerShell. What’s new here is I’ve wrapped the whole concept into a self-contained function complete with a proper parameter block and a (hopefully) adequate degree of error checking. This is a conceptual repeat of the previous article, but there a quite a few improvement and I am personally finding the function to be so useful that I’m loading into memory via my $profile script. Note: be aware that loading this function via the $profile script will cost  you in terms of portability if you create a script that expects the function to be predefined.

Function: NewTempFile

The function is called “NewTempFile” and works as follows: You call NewTempFile passing three optional parameters (explained below) that will result in the creation of a temporary filename (based on your parameters and the current date/time). The function has the ability to create the containing folder(s) if they do not already exist and (as a precaution) will abort in the unlikely event that the generated filename already exists.

The resulting format is DirectoryPath\FilePrefix_YYYYMMDD-hhmmss-mmmm.FileType

Where:

YYYYMMDD = Year Month day (e.g. “20100830″) August 30, 2010
hhmmss = Hour Minute Second (e.g. “100548″) 10:05:48 AM
mmmm = Miliseconds (e.g. “446721″)

Example Temp File Name:

“c:\temp\MyTempFile_20100830-102205-2134.log”

You have complete control over the DirectoryPath, FilePrefix, and FileType components.

Step 1:  Accept Parameters

The three optional Parameters can be specified by name or positionally qualified

<

function NewTempFile() {
Param
 (
 [parameter(Position=0)] [string] $folder="",
 [parameter(Position=1)] [string] $filePrefix="temp",
 [parameter(Position=2)] [string] $fileType="log"
 )

• $folder is the directory path to the location where you want to create your temporary file. If omitted, the file will be created in your current working directory
• $filePrefix is a string of your choosing to make the resulting file easy to recognize. If omitted, “temp” will be used.
• $fileType is a string of your choosing to be appended to the file. If omitted, “.log” will be appended. Note you do not include the period (“.”) when specifying the file type.

Step 2: Create the Folder

<

#create the folder (if needed) if it does not already exist
if ($folder -ne "") {
    if (!(test-path $folder)) {
        write-host "creating new folder `"$folder`"..." -back black -fore yellow
        new-item $folder -type directory | out-null
        }
    if (!($folder.endswith("\"))) {
        $folder += "\"
        }
    }

Not too much to explain here…

• If  $folder is not defined, don’t worry about it, the temp file will be created in the current working directory
• If $folder is defined, test to see if it exist and if not, go ahead and create the directory. Note, the new-item cmdlet will actually create multiple levels of directories in a single call; if you want to specify “c:\level1\level2″ and neither directory exists, the single new-item call will create both directory levels.
• Finally, if the $folder specification ends with a path separator (“\”) find; if not, we append it

Step 3: Generate A Unique filename using the current date/time

<

#generate a unique file name (with path included)
$x = get-date
$TempFile=[string]::format("{0}_{1}{2:d2}{3:d2}-{4:d2}{5:d2}{6:d2}-{7:d4}.{8}",
    $filePrefix,
    $x.year,$x.month,$x.day,$x.hour,$x.minute,$x.second,$x.millisecond,
    $fileType)
 $TempFilePath=[string]::format("{0}{1}",$folder,$TempFile)

Again, fairly straight forward – we’re just getting the current date/time using the get-date cmdlet and then using the [string]::format method to piece all of the filename components together

Step 4: Create the New Temporary File

    #create the new file
    if (!(test-path $TempFilePath)) {
         new-item -path $TempFilePath -type file | out-null
         }
     else {
        throw "File `"$TempFilePath`" Already Exists!"
        }
 return $TempFilePath

• Here we will do a quick check using the test-path cmdlet to make sure that our new temp file does not already exist. Since we’re creating the filename using a timestamp specification down to the milisecond, it’s unlikely to have an error here, but we’ll check anyway and abort with an exception if needed.
• Next we (finally) create the new temporary file
• Lastly, we will return the complete Temporary file path to the calling program so it can be used to write output

If you’ve read this far, I suppose chances are pretty good that you might want to use this function so here it is, ready for download or cut-and-paste from this BLOG to your computer. Once you have downloaded the function, call it like so:

$x = NewTempFile
write-host $x

As always, Enjoy and come back and visit us soon!

Complete “NewTempFile” function:

function NewTempFile() {
Param
    (
    [parameter(Position=0)] [string] $folder="",
    [parameter(Position=1)] [string] $filePrefix="temp",
    [parameter(Position=2)] [string] $fileType="log"
    )
 
    #create the folder (if needed) if it does not already exist
    if ($folder -ne "") {
        if (!(test-path $folder)) {
            write-host "creating new folder `"$folder`"..." -back black -fore yellow
            new-item $folder -type directory | out-null
            }
        if (!($folder.endswith("\"))) {
            $folder += "\"
            }
        }
 
    #generate a unique file name (with path included)
    $x = get-date
    $TempFile=[string]::format("{0}_{1}{2:d2}{3:d2}-{4:d2}{5:d2}{6:d2}-{7:d4}.{8}",
        $filePrefix,
        $x.year,$x.month,$x.day,$x.hour,$x.minute,$x.second,$x.millisecond,
        $fileType)
    $TempFilePath=[string]::format("{0}{1}",$folder,$TempFile)
 
    #create the new file
    if (!(test-path $TempFilePath)) {
        new-item -path $TempFilePath -type file | out-null
        }
    else {
        throw "File `"$TempFilePath`" Already Exists!"
        }
 
    return $TempFilePath
    }