Utils/tail.ps1
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Register-GnuUtil @{ Name = 'tail' Category = 'Viewing file contents' Synopsis = 'Output the last part of files.' Usage = @('tail [OPTION]... [FILE]...') Description = @( 'Print the last 10 lines of each FILE to standard output.', 'With more than one FILE, precede each with a header giving the file name.', '', 'With no FILE, or when FILE is -, read standard input.' ) FileOperands = $true NumericOption = 'n' OpenErrorFormat = "cannot open '{0}' for reading: {1}" ReadErrorFormat = "error reading '{0}': {1}" Options = @( @{ Short = 'f'; Key = 'follow'; Value = 'descriptor'; Help = 'output appended data as the file grows' } @{ Long = 'follow'; Arg = 'HOW'; OptionalArg = $true; Help = 'like -f; --follow=name follows the file name (re-opening it), --follow=descriptor (the default) the open file' } @{ Short = 'F'; Key = 'follow'; Value = 'name'; Sets = @{ retry = 1 }; Help = 'same as --follow=name --retry' } @{ Long = 'max-unchanged-stats'; Arg = 'N'; Help = 'accepted for compatibility (files are always checked by size)' } @{ Long = 'pid'; Arg = 'PID'; Help = 'with -f, terminate after process ID, PID dies' } @{ Long = 'retry'; Help = 'keep trying to open a file if it is inaccessible' } @{ Short = 's'; Long = 'sleep-interval'; Arg = 'N'; Help = 'with -f, sleep for approximately N seconds (default 1.0) between iterations' } @{ Short = 'c'; Long = 'bytes'; Key = 'count'; Arg = '[+]NUM'; Sets = @{ unit = 'bytes' }; Help = 'output the last NUM bytes; or use -c +NUM to output starting with byte NUM of each file' } @{ Short = 'n'; Long = 'lines'; Key = 'count'; Arg = '[+]NUM'; Sets = @{ unit = 'lines' }; Help = 'output the last NUM lines, instead of the last 10; or use -n +NUM to skip NUM-1 lines at the start' } @{ Short = 'q'; Long = 'quiet'; Key = 'headers'; Value = 'never'; Help = 'never output headers giving file names' } @{ Long = 'silent'; Key = 'headers'; Value = 'never'; Help = 'same as --quiet' } @{ Short = 'v'; Long = 'verbose'; Key = 'headers'; Value = 'always'; Help = 'always output headers giving file names' } @{ Short = 'z'; Long = 'zero-terminated'; Help = 'line delimiter is NUL, not newline' } ) Notes = @( 'NUM may have a multiplier suffix:', 'b 512, kB 1000, K 1024, MB 1000*1000, M 1024*1024,', 'GB 1000*1000*1000, G 1024*1024*1024, and so on for T, P, E, Z, Y, R, Q.', 'Binary prefixes can be used, too: KiB=K, MiB=M, and so on.', '', 'With --follow (-f), tail defaults to following the file descriptor, which', 'means that even if a tail''ed file is renamed, tail will continue to track', 'its end. This default behavior is not desirable when you really want to', 'track the actual name of the file, not the file descriptor (e.g., log', 'rotation). Use --follow=name in that case.', '', 'PowerShell note: following stops with Ctrl+C, when --pid dies, or when a later', 'command stops the pipeline (Select-Object -First). Files are polled; an', 'unfinished last line is printed once the file stops growing.' ) } function script:Wait-GnuTailInterval { <# .SYNOPSIS Sleeps between polls of tail -f (mockable in tests). #> param([Parameter(Mandatory)][double]$Seconds) Start-Sleep -Milliseconds ([int][Math]::Max(1, $Seconds * 1000)) } function script:Test-GnuProcessAlive { <# .SYNOPSIS $true while the process with this ID exists (tail --pid). #> param([Parameter(Mandatory)][int]$Id) $null -ne (Get-Process -Id $Id -ErrorAction SilentlyContinue) } function script:Read-GnuTailAppended { <# .SYNOPSIS Reads the bytes of a followed file between its last position and its current end. .OUTPUTS The new text, or $null if nothing changed. Sets Truncated when the file got shorter. #> param([Parameter(Mandatory)][hashtable]$File) $stream = $File.Stream $ownStream = $false if ($null -eq $stream) { try { $stream = New-Object System.IO.FileStream -ArgumentList $File.Path, 'Open', 'Read', 'ReadWrite, Delete' } catch { return $null } $ownStream = $true } try { $length = $stream.Length if ($length -lt $File.Position) { $File.Truncated = $true $File.Position = 0 } if ($length -eq $File.Position) { return $null } $stream.Position = $File.Position $buffer = New-Object byte[] ($length - $File.Position) $read = 0 $count = 1 while ($read -lt $buffer.Length -and $count -gt 0) { $count = $stream.Read($buffer, $read, $buffer.Length - $read) $read += $count } $File.Position += $read $script:GnuUtf8.GetString($buffer, 0, $read) } finally { if ($ownStream) { $stream.Dispose() } } } function script:Invoke-GnuTailFollow { <# .SYNOPSIS tail -f / -F: polls the files and prints what is appended, until --pid dies or the pipeline stops. #> param([Parameter(Mandatory)][hashtable]$Context) $how = [string](Get-GnuOptionValue -Context $Context -Key 'follow') if ([string]::IsNullOrEmpty($how)) { $how = 'descriptor' } if (@('name', 'descriptor') -notcontains $how) { Write-GnuUsageError -Context $Context -Message "invalid argument '$how' for '--follow'`nValid arguments are:`n - 'name'`n - 'descriptor'" return } $interval = 1.0 if (Test-GnuOption -Context $Context -Key 'sleep-interval') { $text = [string](Get-GnuOptionValue -Context $Context -Key 'sleep-interval') if ($text -notmatch '^(\d+\.?\d*|\.\d+)$') { Write-GnuError -Context $Context -Message "invalid number of seconds: '$text'"; return } $interval = [double]::Parse($text, [System.Globalization.CultureInfo]::InvariantCulture) } $processId = $null if (Test-GnuOption -Context $Context -Key 'pid') { $text = [string](Get-GnuOptionValue -Context $Context -Key 'pid') $value = 0 if (-not [int]::TryParse($text, [ref]$value)) { Write-GnuError -Context $Context -Message "invalid PID: '$text'"; return } $processId = $value } $retry = Test-GnuOption -Context $Context -Key 'retry' $operands = @($Context.Operands) if ($operands.Count -eq 0) { $operands = @('-') } $headerMode = [string](Get-GnuOptionValue -Context $Context -Key 'headers' -Default 'auto') $showHeaders = $headerMode -eq 'always' -or ($headerMode -eq 'auto' -and $operands.Count -gt 1) $files = New-Object 'System.Collections.Generic.List[hashtable]' foreach ($operand in $operands) { if ($operand -eq '-') { Write-GnuWarning -Context $Context -Message 'following standard input indefinitely is ineffective' continue } $path = Resolve-GnuPath -Path $operand $file = @{ Name = $operand; Path = $path; Position = [long]0; Stream = $null; Missing = $true; Truncated = $false; Partial = '' } if ([System.IO.File]::Exists($path)) { $file.Missing = $false $file.Position = (New-Object System.IO.FileInfo -ArgumentList $path).Length if ($how -eq 'descriptor') { $file.Stream = New-Object System.IO.FileStream -ArgumentList $path, 'Open', 'Read', 'ReadWrite, Delete' } } elseif (-not $retry) { continue } $files.Add($file) } if ($files.Count -eq 0) { if (@($operands | Where-Object { $_ -ne '-' }).Count -gt 0) { Write-GnuError -Context $Context -Message 'no files remaining' } return } $lastShown = $files[$files.Count - 1].Name try { $finalPass = $false while ($true) { Wait-GnuTailInterval -Seconds $interval if ($null -ne $processId -and -not (Test-GnuProcessAlive -Id $processId)) { $finalPass = $true } foreach ($file in $files) { if ($null -eq $file.Stream) { if (-not [System.IO.File]::Exists($file.Path)) { if (-not $file.Missing) { Write-GnuWarning -Context $Context -Message "'$($file.Name)' has become inaccessible: No such file or directory"; $file.Missing = $true } continue } if ($file.Missing) { Write-GnuWarning -Context $Context -Message "'$($file.Name)' has appeared; following new file" $file.Missing = $false $file.Position = 0 } } $text = Read-GnuTailAppended -File $file if ($file.Truncated) { Write-GnuWarning -Context $Context -Message "$($file.Name): file truncated"; $file.Truncated = $false } if ($null -eq $text) { # The file stopped growing: print an unfinished last line now. if ($file.Partial.Length -gt 0) { $file.Partial; $file.Partial = '' } continue } if ($showHeaders -and $lastShown -ne $file.Name) { ''; "==> $($file.Name) <=="; $lastShown = $file.Name } $text = $file.Partial + $text.Replace("`r`n", "`n") $cut = $text.LastIndexOf("`n") $file.Partial = $text.Substring($cut + 1) if ($cut -ge 0) { ConvertTo-GnuOutputLine -Text $text.Substring(0, $cut + 1) } } if ($finalPass) { foreach ($file in $files) { if ($file.Partial.Length -gt 0) { $file.Partial } } break } } } finally { foreach ($file in $files) { if ($null -ne $file.Stream) { $file.Stream.Dispose() } } } } |