How to set a variable to a column with no header in a tab delimited text file - powershell

Question

Barcode1 Plate # 12/29/2017 07:35:56 EST
A 1 4 5 6
A 1 4 5 6
A 1 4 5 6
A 1 4 5 6
A 1 4 5 6
A 1 4 5 6
A 1 4 5 6
Above is an example of a tab delimited text file. I need to get the data from the column with no header; namely, the columns at the end and I don't know how to identify it. I am trying to swap columns and output a text file. The source data file format is the same every time.
This is part of what I have:
$swapColumns = #{
column1 = #{
name = "date-header"
instance = 1
}
column2 = #{
name = "Blank"
instance = 1
}
}
$formats = #(
'XR-{0:yyyyMMdd}-01.txt'
)
$date = [datetime]::now
$ErrorActionPreference = 'Stop'
function Get-HeaderIndex {
param(
[System.Collections.Generic.List[string]]$Source,
[string]$Header,
[uint16]$Instance
)
$index = 0;
for ($i = 0; $i -lt $Instance; $i++) {
$index = $Source.IndexOf($Header, $index, ($Source.Count - $index))
if (($index -eq -1) -or (($i + 1) -eq $Instance)) {
break
}
$index = $index + 1
}
if ($index -eq -1) { throw "index not found" }
return $index
}
#grabs the first item in folder matching UCX-*.txt
$fileDetails = Get-ChildItem $PSScriptRoot\UCX-*.txt | select -First 1
#gets the file contents
$file = Get-Content $fileDetails
#break up script in sections that look like '======section======'
#and store the section name and line number it starts on
$sections = #()
for ($i = 0; $i -lt $file.Count; $i++) {
if ($file[$i] -match '^=+(\w+)=+$') {
$section = $Matches[1]
$sections += [pscustomobject]#{line = $i; header = $section}
}
}
#get the data section
$dataSection = $sections | ? {$_.header -eq 'data'}
#get the section following data
$nextSection = $sections | ? {$_.line -gt $dataSection.line} | sort
-Property line | select -First 1
#get data column headers
$dataHeaders = New-Object System.Collections.Generic.List[string]
$file[$dataSection.line + 1].split("`t") | % {
[datetime]$headerDateValue = [datetime]::MinValue
$headerIsDate = [datetime]::TryParse($_.Replace('EST','').Trim(),
[ref] $headerDateValue)
if ($headerIsDate) {
$dataHeaders.Add('date-header')
}
else {
$dataHeaders.Add($_)
}
}
#get index of columns defined in $swapColumns
$column1 = Get-HeaderIndex -Source $dataHeaders -Header
$swapColumns.column1.name -Instance $swapColumns.column1.instance
$column2 = Get-HeaderIndex -Source $dataHeaders -Header
swapColumns.column2.name -Instance $swapColumns.column2.instance
#iterate over each row in data section, swap data from column1/column2
for ($i = $dataSection.line + 2; $i -lt $nextSection.line - 1; $i++) {
$line = $file[$i]
$parts = $line.split("`t")
$tmp1 = $parts[$column1]
$parts[$column1] = $parts[$column2]
$parts[$column2] = $tmp1
$file[$i] = $parts -join "`t"
}
#write new file contents to files with names defined in $formats
$formats | % {
$file | Out-File ($_ -f $date) -Force
}

Answer 1

If you know what your file format is going to be then forget whatever the current header is and assume when we convert the file to a CSV object.
It looks like you need to parse the date of out the header which should be trivial. Grab it from $fileheader however you would like.
$wholeFile = Get-Content C:\temp\test.txt
$fileHeader = $wholeFile[0] -split "`t"
$newHeader = "Barcode1", "Plate #", "Date", "Plumbus", "Dinglebop"
$wholeFile |Select-Object -Skip 1 | ConvertFrom-Csv -Delimiter "`t" -Header $newHeader

Answer 2

If the columns length is always the same, there's another option, specify manually the width of the columns, See example:
$content = Get-Content C:\temp.tsv
$columns = 13, 24, 35 | Sort -Descending
$Delimiter = ','
$Results = $content | % {
$line = $_
$columns | % {
$line = $line.Insert($_, $Delimiter)
}
$line
} |
ConvertFrom-Csv -Delimiter $Delimiter
Results:
Barcode1 Plate # H1 12/29/2017 07:35:56 EST
--------- ----------- -- -----------------------
A 1 4 5
A 1 4 5
A 1 4 5
A 1 4 5
A 1 4 5
A 1 4 5
A 1 4 5
Then you can easily get the data you need:
$Results[0].H1
4

Answer 3

[This answer doesn't solve the OP's problem after clarifying the exact requirements, but may be of general interest to some, given the question's generic title.]
If the file is really tab-delimited, you can use Import-Csv -Delimiter "`t" to read it, in which case PowerShell will autogenerate header names as H<n> if they're missing, where <n> is a sequence number starting with 1.
Caveat: This doesn't work if the unnamed column is the last one, because - inexplicably - Import-Csv then ignores the entire column (more generally, any run of trailing delimiters).
Import-Csv -Delimiter "`t" file.tsv | Select-Object -ExpandProperty H1