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Powershell Notes

Tools

Package Repo and Management

PowerShell office (managed by MS) package repo: PowerShell Gallery.

Package manager: PowerShellGet Install it with Install-Module -Name PowerShellGet -Force.

Install package with Install-Module -Name ... like the following ZLocation.

PowerShell directory auto jump

Install ZLocation with Install-Module -Name ZLocation. Like autojump (j) in shell, jump with z command.

Development

Comment

# for line; <# ... #> for block

Ref: https://stackoverflow.com/questions/7342597/how-do-you-comment-out-code-in-powershell

Test object type

write-host $res.GetType().fullname   # write-host = println
if ($res -is [string]) {write-host "this is a string"}
if ($res -is [array]) {write-host "this is a array"}

Ref:

  • http://thephuck.com/scripts/easy-way-to-check-if-your-powershell-variable-is-an-array-or-not/

List properties and methods of an object

Use Get-Member:

$curTime = Get-Date                  # DateTime object
$timeStr = $curTime.ToString()       # String
$dt = [datetime]::Parse($timeStr)    # DateTime object
$dt | Get-Member                     # list props and methods

Convert result to array

Use @().

Ref: Powershell Test if array in one line

map array

Or list comprehension. For example, map a string array to an object array: $fileNameArr | % { Get-Item $_ }. Here % means foreach, $_ denote each element of the array.

Load variables from another powershell script

Use ./fileToLoad.ps1.

Ref:

  • https://stackoverflow.com/questions/1864128/load-variables-from-another-powershell-script

  • https://stackoverflow.com/questions/27138483/how-can-i-re-use-import-script-code-in-powershell-scripts

File IO

Write to file

Write string $res to file path $lastResult: $res | out-file -encoding UTI8 $lastResult

Here -encoding is mandatory, or the english characters will be written as full-width characters.

Write string $timeStr to file path $lastSync: [System.IO.File]::WriteAllLines($lastSync, $timeStr)

But why files created by these 2 methods are all have 'x' attributes?

Ref:

  • https://stackoverflow.com/questions/19122755/output-echo-a-variable-to-a-text-file

  • https://stackoverflow.com/questions/5596982/using-powershell-to-write-a-file-in-utf-8-without-the-bom

  • Out- File API

Head/tail of an array

Empty array: @()

All except first 3 items: 1..10 | Select-Object -skip 3

First 3 items: 1..10 | Select-Object -first 3

Last 3 items: 1..10 | Select-Object -last 3

Middle 4 items: 1..10 | Select-Object -skip 3 -first 4

Ref: https://stackoverflow.com/questions/10079572/powershell-equivalent-for-head-n-3

Get file attributes

$updated = Get-Date (Get-Item $fullname).LastWriteTime

Ref: https://stackoverflow.com/questions/19774097/finding-modified-date-of-a-file-folder

Print a certain line of a file with PowerShell

Or get a selected item from an index: (Get-Content file.txt)[4]

Ref: https://stackoverflow.com/questions/14759649/how-to-print-a-certain-line-of-a-file-with-powershell

Parse and format Time

default format

Get current time: $timeStr = Get-Date

Custom format

Get time from file and print as string: $updated = Get-Date (Get-Item $fullname).LastWriteTime -format "yy.M.d H:m"

String -> DateTime -> String: 

$y = [datetime]::ParseExact($createdStr, "yyyy-MM-dd HH:mm:ss", [Globalization.CultureInfo]::InvariantCulture)
$created = $y.ToString("yy.M.d H:m")

Ref:

  • https://technet.microsoft.com/en-us/library/ee692801.aspx

  • https://stackoverflow.com/questions/27741810/string-to-datetime-conversion-in-powershell

  • https://stackoverflow.com/questions/2249619/how-to-format-a-datetime-in-powershell

Run Powershell script in Winodws console

You have to add -file flag for a non-command PS script: powershell -file donshell.ps1 s reduce

Ref: https://stackoverflow.com/questions/13724940/how-to-run-a-powershell-script-from-the-command-line-and-pass-a-directory-as-a-p

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