"-----start-------Hello World------end-------"

Hello World

PS C:> $x = "----start----Hello World----end----"
PS C:> $x -match "----start----(?<content>.*)----end----"
True
PS C:> $matches['content']
Hello World

PS > "test_string".Substring(0,4)
Test
PS > "test_string".Substring(4)
_stringPS >

$s = 'Hello World is in here Hello World!'
 $p = 'Hello World'
 $s -match $p

dir -rec -filter *.txt | Select-String 'Hello World'

$String="----start----`nHello World`n----end----"
$SearchStart="----start----`n" #Will not be included in results
$SearchEnd="`n----end----" #Will not be included in results
$String -match "(?s)$SearchStart(?<content>.*)$SearchEnd"
$result=$matches['content']
$result

$String=[string]::join("`n", (Get-Content $Filename))

$line = "----start----Hello World----end----"
$line -match "Hello World"
$matches[0]
Hello World

$result = $matches[0]
$result
Hello World