powershell file timestamp pipe system-administration

How to create an empty log or text file with Powershell using date or timestamp?

How to create an empty file with powershell, similar to "touch" on Linux, with a timestamp in the filename?

not too different from:

md5sum /etc/mtab > "$(date +"%Y_%m_%d_%I_%M_%p").log"

although that file isn't actually empty, but it does have the date incorporated into the filename itself.

Attempts on Powershell:

PS /home/nicholas/powershell/file_ops> New-Item -ItemType file  foo.txt

New-Item: The file '/home/nicholas/powershell/file_ops/foo.txt' already exists.

New-Item: The file '/home/nicholas/powershell/file_ops/foo.txt' already exists.
PS /home/nicholas/powershell/file_ops> New-Item -ItemType file  bar.txt

    Directory: /home/nicholas/powershell/file_ops

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
-----          12/20/2020 10:56 AM              0 bar.txt

PS /home/nicholas/powershell/file_ops> $logfile = "./"+$FN+"-LOG-AddUser_$(get-date -Format yyyymmdd_hhmmtt).txt"

ideally, to generate an arbitrary number of empty log or text files.

https://superuser.com/q/502374/977796

https://4sysops.com/archives/understanding-the-powershell-_-and-psitem-pipeline-variables/

https://unix.stackexchange.com/q/278939/101935

Solution

In the simplest case, if you want to unconditionally create a file, use New-Item -Force - but note that if the target file exists, its content is discarded:

# CAVEAT: Truncates an existing file. `-ItemType File` is implied.
#  * Outputs a [System.IO.FileInfo] instance describing the new file, which
# $null = ... discards here.
#  * `Get-Date -UFormat` allows you to perform Unix-style date formatting.
$null = New-Item -Force "$(Get-Date -UFormat "%Y_%m_%d_%I_%M_%p").log"

New-Item's (positionally implied) -Path parameter supports an array of paths, so you can pass multiple paths at once.
By default, an empty file is created, but you may optionally provide (initial) content via the -Value parameter.

More work is needed if you truly want to emulate the touch Unix utility's behavior, which by default means (note that touch supports a variety of options^[1]):

If a file doesn't exist yet, create it (as an empty file).
Otherwise, update the last-modified timestamp to the current point in time (and leave the existing content alone).

$file = "$(Get-Date -UFormat "%Y_%m_%d_%I_%M_%p").log"
# Trick: This dummy operation leaves an existing file alone,
#        but creates the file if it doesn't exist.
Add-Content -LiteralPath $file -Value $null
(Get-Item -LiteralPath $file).LastWriteTime = Get-Date

Note:

The above is limited to a single file specified by literal path, and doesn't include error handling.
See this answer for custom PowerShell function Touch-File, which implements most of the touch utility's functionality in PowerShell-idiomatic fashion, including the ability to handle wildcard patterns correctly.
- Said function is also available as an MIT-licensed Gist. Assuming you have looked at the linked code to ensure that it is safe (which I can personally assure you of, but you should always check), you can install it directly as follows:
```
irm https://gist.github.com/mklement0/82ed8e73bb1d17c5ff7b57d958db2872/raw/Touch-File.ps1 | iex
```

^{[1] The linked page is touch's POSIX spec, which mandates minimum functionality; concrete implementations may support more.}