Powershell concatenate two files

Question

I have a file 1.txt with content:

Package1
Package2
Package3
Package4

And another file 2.txt

Version
VersionExtend
Version
VersionExtend

I just want to concatenate these strings with a delimiter, which will be like below:

Package1:Version
Package2:VersionExtend
Package3:Version
Package4:VersionExtend

I tried

Get-Content 1.txt, 2.txt | Set-Content joinedFile.txt

But got this result:

Package1
Package2
Package3
Package4
Version
VersionExtend
Version
VersionExtend

Can you give me ideas on how to do it?

For some time now, I [purposed a `Join-Object`](https://github.com/PowerShell/PowerShell/issues/14994) cmdlet to be put in the standard PowerShell equipment which the main goal to get an easier *PowerShell* syntax for joining object lists (including scalar list as in [a few other questions](https://stackoverflow.com/a/68070763/1701026)). For the [purposed `Join-Object`](https://stackoverflow.com/a/45483110/1701026) cmdlet, the command for this question would be something like `Get-Content .\FileA.txt |Join-Object (Get-Content .\FileB.txt) |ForEach-Object { $_ -Join ';' }` — iRon, Jul 10 '22 at 08:37

mklement0 · Accepted Answer · 2022-07-10T12:08:07.743

You're simply writing the content of the two files one after the other instead of processing corresponding lines.

PowerShell has no built-in way for enumerating collections by positionally corresponding elements,^[1] but you can use .NET APIs:

# IMPORTANT:
# Since .NET's working dir. usually differs from PowerShell's, it
# is important to always use FULL PATHS when calling .NET methods.
# The calls to Convert-Path ensure that.

# Get enumerators for the lines of both files.
$fileA = [System.IO.File]::ReadLines((Convert-Path 1.txt))
$fileB = [System.IO.File]::ReadLines((Convert-Path 2.txt))

# Iterate over the files' lines in tandem, and write each pair
# to the output file.
& {
  while ($fileA.MoveNext(), $fileB.MoveNext() -contains $true) {
    '{0}:{1}' -f $fileA.Current, $fileB.Current
  }
} | Set-Content joinedFile.txt

This solution is memory-friendly, as it reads the lines lazily, i.e., on demand, using the System.IO.File.ReadLines method, obviating the need to read the files into memory as a whole.
If one of the files "runs out lines", an empty string is used in lieu of a value.
- If you want to limit processing to only as many lines as the two files have in common, replace the while condition with:
```
while ($fileA.MoveNext(), $fileB.MoveNext() -notcontains $false)
```
- Alternatively, use a LINQ-based solution, as shown next.

LINQ-based solutions:

Important: The solutions below use the System.Linq.Enumerable.Zip method, which assumes that the the input collections have the same number of elements. If they differ in element count, processing is invariably limited to as many elements as the smaller collection has, i.e. to how many elements they have in common.

Memory-friendly too:

# Get enumerators for the lines of both files.
$fileA = [System.IO.File]::ReadLines((Convert-Path 1.txt))
$fileB = [System.IO.File]::ReadLines((Convert-Path 2.txt))

[Linq.Enumerable]::Zip(
  $fileA,
  $fileB,
  [Func[string, string, string]] { '{0}:{1}' -f $args[0], $args[1] }
) | Set-Content joinedFile.txt

Simpler alternative that reads both files in full first:

[Linq.Enumerable]::Zip(
  (Get-Content -ReadCount 0 1.txt),
  (Get-Content -ReadCount 0 2.txt),
  [Func[object, object, string]] { '{0}:{1}' -f $args[0], $args[1] }
) | Set-Content joinedFile.txt

^{[1] A proposal to introduce such a feature, in the form of foreach ($elementFromA, $elementFromB in $collectionA, $collectionB) { ... }, was rejected, unfortunately - see GitHub issue #14732.}

Powershell concatenate two files

1 Answers1