ConvertPermission.ps1

# 八進表記から記号表記に変換
function ConvertPermissionNumberToString($target) {
  $res = $target
  
  # 特殊権限への対応（事前判定と除去）
  $sp = ""
  if($res.Length -eq 4){
    $sp = $res[0]
    $res = $res.Remove(0,1)
  }
  
  # 手っ取り早く総当りで変換
  $res = $res -replace 0,"---"
  $res = $res -replace 1,"--x"
  $res = $res -replace 2,"-w-"
  $res = $res -replace 3,"-wx"
  $res = $res -replace 4,"r--"
  $res = $res -replace 5,"r-x"
  $res = $res -replace 6,"rw-"
  $res = $res -replace 7,"rwx"
  
  # 特殊権限への対応（所定位置の特定の文字を入れ替える）
  function ConvertSUID($res){
    if($res[2] -eq "x"){
      $res = $res.Insert(3, "s")
    }else{
      $res = $res.Insert(3, "S")
    }
    $res = $res.Remove(2, 1)
    return $res
  }
  function ConvertSGID($res){
    if($res[5] -eq "x"){
      $res = $res.Insert(6, "s")
    }else{
      $res = $res.Insert(6, "S")
    }
    $res = $res.Remove(5, 1)
    return $res
  }
  function ConvertSticky($res){
    if($res[8] -eq "x"){
      $res = $res.Insert(9, "t")
    }else{
      $res = $res.Insert(9, "T")
    }
    $res = $res.Remove(8, 1)
    return $res
  }

  switch($sp){
    "1" {
      $res = ConvertSUID $res
    }
    "2" {
      $res = ConvertSGID $res
    }
    "3" {
      $res = ConvertSUID $res
      $res = ConvertSGID $res
    }
    "4" {
      $res = ConvertSticky $res
    }
    "5" {
      $res = ConvertSUID $res
      $res = ConvertSticky $res
    }
    "6" {
      $res = ConvertSGID $res
      $res = ConvertSticky $res
    }
    "7" {
      $res = ConvertSUID $res
      $res = ConvertSGID $res
      $res = ConvertSticky $res
    }
  }

  return ($res.ToString())
}


# 記号表記から八進表記に変換
function ConvertPermissionStringToNumber($target) {
  $res = $target

  # SELinux対策（最後尾が.だったら消す）
  if($res[-1] -eq "."){
    $res = $res -replace "\.",""
  }
  # ファイル種別まで指定されていたら（指定文字数が10文字だったら）先頭１文字を消す
  if($res.Length -eq 10){
    $res = $res.Remove(0, 1)
  }

  # 特殊権限への対応
  $sp = 0
  if($res[2] -eq "s"){ $sp += 1 }  # SUID
  if($res[5] -eq "s"){ $sp += 2 }  # SGID
  if($res[8] -eq "t"){ $sp += 4 }  # Sticky

  # 一時的に「,」で3文字ずつに分割（誤変換防止）
  $res = $res.Insert(3, ",")
  $res = $res.Insert(7, ",")
  
  # 手っ取り早く総当りで変換
  $res = $res -creplace "s","x"
  $res = $res -creplace "t","x"
  $res = $res -creplace "S","-"
  $res = $res -creplace "T","-"
  $res = $res -replace "---",0
  $res = $res -replace "--x",1
  $res = $res -replace "-w-",2
  $res = $res -replace "-wx",3
  $res = $res -replace "r--",4
  $res = $res -replace "r-x",5
  $res = $res -replace "rw-",6
  $res = $res -replace "rwx",7

  # 一時的に入れた「,」を消去
  $res = $res -replace ",",""

  return ($sp.ToString() + $res.ToString())
}

TestCode

# テスト
$arr = @(
"0777"
"0000"
"0123"
"0321"
"0755"
"1755"
"2755"
"3755"
"4755"
"5755"
"6755"
"7755"
"0644"
"7644"
"7777"
"7666"
)

echo ("Convert`tsource`tdestination")
$arr | %{
  echo ("-----")
  $res1 = ConvertPermissionNumberToString $_
  echo ("8進 → rwx:`t" + $_ + "`t" + $res1)
  $res2 = ConvertPermissionStringToNumber $res1
  echo ("rwx → 8進:`t" + $res1 + "`t" + $res2)

  # 再変換した結果が入力と一致していたらOK
  if($_ -eq $res2){echo "○"}else{echo "×"}
}


### 実行結果
Convert	source	destination
-----
8進 → rwx:	0777	rwxrwxrwx
rwx → 8進:	rwxrwxrwx	0777
○
-----
8進 → rwx:	0000	---------
rwx → 8進:	---------	0000
○
-----
8進 → rwx:	0123	--x-w--wx
rwx → 8進:	--x-w--wx	0123
○
-----
8進 → rwx:	0321	-wx-w---x
rwx → 8進:	-wx-w---x	0321
○
-----
8進 → rwx:	0755	rwxr-xr-x
rwx → 8進:	rwxr-xr-x	0755
○
-----
8進 → rwx:	1755	rwsr-xr-x
rwx → 8進:	rwsr-xr-x	1755
○
-----
8進 → rwx:	2755	rwxr-sr-x
rwx → 8進:	rwxr-sr-x	2755
○
-----
8進 → rwx:	3755	rwsr-sr-x
rwx → 8進:	rwsr-sr-x	3755
○
-----
8進 → rwx:	4755	rwxr-xr-t
rwx → 8進:	rwxr-xr-t	4755
○
-----
8進 → rwx:	5755	rwsr-xr-t
rwx → 8進:	rwsr-xr-t	5755
○
-----
8進 → rwx:	6755	rwxr-sr-t
rwx → 8進:	rwxr-sr-t	6755
○
-----
8進 → rwx:	7755	rwsr-sr-t
rwx → 8進:	rwsr-sr-t	7755
○
-----
8進 → rwx:	0644	rw-r--r--
rwx → 8進:	rw-r--r--	0644
○
-----
8進 → rwx:	7644	rwSr-Sr-T
rwx → 8進:	rwSr-Sr-T	7644
○
-----
8進 → rwx:	7777	rwsrwsrwt
rwx → 8進:	rwsrwsrwt	7777
○
-----
8進 → rwx:	7666	rwSrwSrwT
rwx → 8進:	rwSrwSrwT	7666
○