如何通过powershell将每一行文本文件保存为数组

Question

If I have a text file, C:\USER\Documents\Collections\collection.txt that has the following information:

collectionA.json
collectionB.json
collectionC.json
collectionD.json

I am wondering how, through Powershell, I am able to store each line in the text file as elements of an array such as..

array arrayFromFile = new Array;
foreach(line x in collection.txt)
{
    arrayFromFile.Add(x);
}

..with the end goal of doing the following:

foreach(string x in arrayFromFile)
{
    newman run x;
}

My apologies for the seemingly easy question - I have never dealt with Powershell before.

Answer 1

The Get-Content command returns each line from a text file as a separate string, so will give you an array (so long as you don't use the -Raw parameter; which causes all lines to be combined to a single string).

[string[]]$arrayFromFile = Get-Content -Path 'C:\USER\Documents\Collections\collection.txt'

In his excellent answer , mklement0 gives a lot more detail on what's really going on when you call this command, as well as alternate approaches if you're concerned about performance over convenience. Definitely worth a read if you're interested in learning more about the language rather than just solving this one off requirement.

Answer 2

To complement JohnLBevan's helpful answer :

Get-Content , as a cmdlet , outputs objects one by one to the pipeline , as they become available . (Note that a pipeline is involved even when invoking a cmdlet in the absence of the pipe symbol, | , the latter being required for chaining multiple commands).
In this case, the output objects are the individual lines of the input text file.

If you collect a pipeline's output objects , such as by assigning it to a variable such as $arrayFromFile or by using the pipeline in the context of a larger expression with (...) :

• PowerShell captures multiple output objects in an automatically created array , of type [object[]] ,
• but if there's only one output object, that object is captured as-is ( without an array wrapper)

However, it often isn't necessary to ensure that you always receive an array , because PowerShell treats scalars (single values that aren't collections) the same as arrays (collections) in many contexts, such as in foreach statements or when outputting a value to be enumerated to the pipeline, to be processed via the ForEach-Object cmdlet, for instance; therefore, the following commands work just fine, irrespective of how many lines the input file contains:

# OK - read all lines, then process them one by one in the loop.
# (No strict need to collect the Get-Content output in a variable first.)
foreach ($line in Get-Content C:\USER\Documents\Collections\collection.txt) {
  newman run $line
}

# Alternative, using the pipeline:
# Read line by line, and pass each through the pipeline, as it is being
# read, to the ForEach-Object cmdlet.
# Note the use of automatic variable $_ to refer to the line at hand.
Get-Content C:\USER\Documents\Collections\collection.txt |
  ForEach-Object { newman run $_ }

---

In order to ensure that a command's output is always an array, PowerShell offers @(...) , the array-subexpression operator , which wraps even single-object output in an array.

Therefore, the PowerShell-idiomatic solution is:

$arrayFromFile = @(Get-Content C:\USER\Documents\Collections\collection.txt)

TheMadTechnician points out that you can also use [array] to cast / type-constrain pipeline output as an alternative to @(...) , which also creates [object[]] arrays :

# Equivalent of the command above that additionally locks in the variable date type.
[array] $arrayFromFile = Get-Content C:\USER\Documents\Collections\collection.txt

By using [array] $arrayFromFile = ... rather than $arrayFromFile = [array] (...) , variable $arrayFromFile becomes type-constrained , which means that its data type is locked in (whereas by default PowerShell allows you to change the type of a variable anytime).

[array] is a command-independent alternative to the type-specific cast used in John's answer, [string[]] ; you may use the latter for enforcing use of a uniform type across the array's elements, but that is often not necessary in PowerShell ^[1] .

Regular PowerShell arrays are of type [object[]] , which allows mixing elements of different types, but any given element still has a specific type; eg, even though the type of $arrayFromFile after the command above is [object[]] , the type of $arrayFromFile[0] , ie the 1st element, for instance, is [string] (assuming that the file contained at least 1 line; verify the type with $arrayFromFile[0].GetType().Name ).

---

Faster alternative: direct use of the .NET framework

Cmdlets and the pipeline offer high-level, potentially memory-throttling features that are expressive and convenient, but they can be slow .

When performance matters, direct use of .NET framework types is necessary, such as [System.IO.File] in this case.

$arrayFromFile = [IO.File]::ReadAllLines('C:\USER\Documents\Collections\collection.txt')

^{Note how the System. prefix can be omitted from the type name.}

• As in John's answer, this will return a [string[]] array.

• Caveats :

  • Be careful with relative paths, as .NET typically has a different current directory than PowerShell; to work around this, always pass absolute paths , in the simplest case with, eg, "$PWD/collection.txt" and most robustly with
    "$((Get-Location -PSProvider FileSystem).ProviderPath)/collection.txt"

  • .NET's default encoding is UTF-8, whereas Windows PowerShell defaults to "ANSI" encoding , iethe system locale's legacy code page; PowerShell Core (v6+), by contrast, also defaults to UTF-8 . Use Get-Encoding 's -Encoding parameter or the .ReadAllLines() overload that accepts an encoding instance to specify the input file's character encoding explicitly.

---

^{[1] Generally, PowerShell's implicit, runtime type conversions cannot provide the same type safety you'd get in C#, for instance. Eg, [string[]] $a = 'one', 'two'; $a[0] = 42 [string[]] $a = 'one', 'two'; $a[0] = 42 does not cause an error: PowerShell simply quietly converts [int] 42 to a string.}

Answer 3

$array = Get-Content -Path @("C:\tmp\sample.txt")
foreach($item in $array)
{
 write-host $item 
}