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Dev. PowerShell random solutions‚Äč

Mathias R. Jessen: Normally you would use $? to inspect the status of the last statement executed:

PS C:\> Write-Output 123 | Out-Null; $?
True
PS C:\> Non-ExistingCmdlet 123 | Out-Null; $?
False

However, this won't work with Invoke-Expression, because even though a statement inside the expression passed to Invoke-Expression may fail, the Invoke-Expression call it self will have succeeded (ie. the expression, although invalid/non-functional was invoked none the less)


With Invoke-Expression you'll have to use try:

try {
Invoke-Expression "Do-ErrorProneAction -Parameter $argument"
} catch {
# error handling go here, $_ contains the error record
}

or a trap:

trap {
# error handling goes here, $_ contains the error record
}
Invoke-Expression "More-ErrorProneActions"


The alternative is the append ";$?" to the expression you want to invoke:

$Expr  = "Write-Host $SomeValue"
$Expr += ';$?'

$Success = Invoke-Expression $Expr
if(-not $Success){
# seems to have failed
}

but relies on there not being any pipeline output

  • 2022-04-12 How to Use PowerShell's Grep Select-String

    One of the first Linux commands that many system administrators learn is grep. This venerable tool has been around for decades and is crucial to any administrator’s toolbelt. Grep’s core is simply the ability to search plain text for a RegEx pattern. Grep can search files in a given directory or streamed input to output matches. Did you know PowerShell has grep? Well..almost.

Select-String -Path "Users\*.csv" -Pattern "Joe","Marti","Jerry"

Encoder Script‚Äč

function Base64Encode($s) {
$i = 0
$base64 = $ending = ''
$base64chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'

# Add padding if string is not dividable by 3
$pad = 3 - ($s.length % 3)
if ($pad -ne 3) {
$s += "A" * $pad
$ending = "=" * $pad
}
# Iterate though the whole input string
while ($i -lt $s.length) {
# Take 3 characters at a time, convert them to 4 base64 chars
$b = 0
for ($j=0; $j -lt 3; $j++) {

# get ASCII code of the next character in line
$ascii = [int][char]$s[$i]
$i++

# Concatenate the three characters together
$b += $ascii -shl 8 * (2-$j)
}

# Convert the 3 chars to four Base64 chars
$base64 += $base64chars[ ($b -shr 18) -band 63 ]
$base64 += $base64chars[ ($b -shr 12) -band 63 ]
$base64 += $base64chars[ ($b -shr 6) -band 63 ]
$base64 += $base64chars[ $b -band 63 ]
}
# Add the actual padding to the end after removing the same number of characters
if ($pad -ne 3) {
$base64 = $base64.SubString(0, $base64.length - $pad)
$base64 += $ending
}
# Return the Base64 encoded result
return $base64
}

Decoder Script‚Äč

function Base64Decode($s) {
$i = 0
$base64 = $decoded = ''
$base64chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
# Replace padding with "A" characters for the decoder to work and save the length of the padding to be dropped from the end later
if ($s.substring($s.length - 2,2) -like "==") {
$s = $s.substring(0, $s.length - 2) + "AA"
$padd = 2
}
elseif ($s.substring($s.length - 1,1) -like "=") {
$s = $s.substring(0, $s.length - 1) + "A"
$padd = 1
}
# Take 4 characters at a time
while ($i -lt $s.length) {
$d = 0

for ($j=0; $j -lt 4; $j++) {
$d += $base64chars.indexof($s[$i]) -shl (18 - $j * 6)
$i++
}
# Convert the 4 chars back to ASCII
$decoded += [char](($d -shr 16) -band 255)
$decoded += [char](($d -shr 8) -band 255)
$decoded += [char]($d -band 255)
}
# Remove padding
$decoded = $decoded.substring(0, $decoded.length - $padd)
# Return the Base64 encoded result
return $decoded
}

Aliases‚Äč

From 2022-04-11 PowerShell - Aliases

aliascmdlet
%, foreachFor-EachObject
?, whereWhere-Object
cat, gc, typeGet-Content
cd, chdir, slSet-Location
cls, clearClear-Host
cp, copy, cpiCopy-Item
dir/ls/gciGet-ChildItem
echo, writeWrite-Output
flFormat-List
ftFormat-Table
fwFormat-Wide
gc, pwdGet-Location
gmGet-Member
iexInvoke-Expression
iiInvoke-Item
mv, moveMove-Item
rm, rmdir, del, erase, rd, riRemove-Item
sleepStart-Sleep
start, sapsStart-Process