PowerShellのパイプ処理の考え方

前コマンドレットの出力オブジェクトが後続のコマンドレットのインプットになる。

インプットのオブジェクトが配列の場合、要素が一個づつ後続のコマンドレットにより処理される。

後続のコマンドは、パイプ対応コマンドもしくは、foreach-objectコマンドで受けることが可能。

パイプ対応コマンドで受ける例

クリックで動作メモ表示

> (1,2) | Get-Member


   TypeName: System.Int32

Name        MemberType Definition
----        ---------- ----------
CompareTo   Method     int CompareTo(System.Object value), int CompareTo(int value), int IComparable.CompareTo(Syst...
Equals      Method     bool Equals(System.Object obj), bool Equals(int obj), bool IEquatable[int].Equals(int other)
GetHashCode Method     int GetHashCode()
GetType     Method     type GetType()
GetTypeCode Method     System.TypeCode GetTypeCode(), System.TypeCode IConvertible.GetTypeCode()
ToBoolean   Method     bool IConvertible.ToBoolean(System.IFormatProvider provider)
ToByte      Method     byte IConvertible.ToByte(System.IFormatProvider provider)
ToChar      Method     char IConvertible.ToChar(System.IFormatProvider provider)
ToDateTime  Method     datetime IConvertible.ToDateTime(System.IFormatProvider provider)
ToDecimal   Method     decimal IConvertible.ToDecimal(System.IFormatProvider provider)
ToDouble    Method     double IConvertible.ToDouble(System.IFormatProvider provider)
ToInt16     Method     int16 IConvertible.ToInt16(System.IFormatProvider provider)
ToInt32     Method     int IConvertible.ToInt32(System.IFormatProvider provider)
ToInt64     Method     long IConvertible.ToInt64(System.IFormatProvider provider)
ToSByte     Method     sbyte IConvertible.ToSByte(System.IFormatProvider provider)
ToSingle    Method     float IConvertible.ToSingle(System.IFormatProvider provider)
ToString    Method     string ToString(), string ToString(string format), string ToString(System.IFormatProvider pr...
ToType      Method     System.Object IConvertible.ToType(type conversionType, System.IFormatProvider provider)
ToUInt16    Method     uint16 IConvertible.ToUInt16(System.IFormatProvider provider)
ToUInt32    Method     uint32 IConvertible.ToUInt32(System.IFormatProvider provider)
ToUInt64    Method     uint64 IConvertible.ToUInt64(System.IFormatProvider provider)

2個のオブジェクトに対して実行されたが、二つのオブジェクトのタイプが同じであるため、出力結果は一つになってる。

foreach-objectコマンドで受ける例

クリックで動作メモ表示

> (1,2) | ForEach-Object {$_ | Get-Member }


   TypeName: System.Int32

Name        MemberType Definition
----        ---------- ----------
CompareTo   Method     int CompareTo(System.Object value), int CompareTo(int value), int IComparable.CompareTo(Syst...
Equals      Method     bool Equals(System.Object obj), bool Equals(int obj), bool IEquatable[int].Equals(int other)
GetHashCode Method     int GetHashCode()
GetType     Method     type GetType()
GetTypeCode Method     System.TypeCode GetTypeCode(), System.TypeCode IConvertible.GetTypeCode()
ToBoolean   Method     bool IConvertible.ToBoolean(System.IFormatProvider provider)
ToByte      Method     byte IConvertible.ToByte(System.IFormatProvider provider)
ToChar      Method     char IConvertible.ToChar(System.IFormatProvider provider)
ToDateTime  Method     datetime IConvertible.ToDateTime(System.IFormatProvider provider)
ToDecimal   Method     decimal IConvertible.ToDecimal(System.IFormatProvider provider)
ToDouble    Method     double IConvertible.ToDouble(System.IFormatProvider provider)
ToInt16     Method     int16 IConvertible.ToInt16(System.IFormatProvider provider)
ToInt32     Method     int IConvertible.ToInt32(System.IFormatProvider provider)
ToInt64     Method     long IConvertible.ToInt64(System.IFormatProvider provider)
ToSByte     Method     sbyte IConvertible.ToSByte(System.IFormatProvider provider)
ToSingle    Method     float IConvertible.ToSingle(System.IFormatProvider provider)
ToString    Method     string ToString(), string ToString(string format), string ToString(System.IFormatProvider pr...
ToType      Method     System.Object IConvertible.ToType(type conversionType, System.IFormatProvider provider)
ToUInt16    Method     uint16 IConvertible.ToUInt16(System.IFormatProvider provider)
ToUInt32    Method     uint32 IConvertible.ToUInt32(System.IFormatProvider provider)
ToUInt64    Method     uint64 IConvertible.ToUInt64(System.IFormatProvider provider)
★ここから2個目
CompareTo   Method     int CompareTo(System.Object value), int CompareTo(int value), int IComparable.CompareTo(Syst...
Equals      Method     bool Equals(System.Object obj), bool Equals(int obj), bool IEquatable[int].Equals(int other)
GetHashCode Method     int GetHashCode()
GetType     Method     type GetType()
GetTypeCode Method     System.TypeCode GetTypeCode(), System.TypeCode IConvertible.GetTypeCode()
ToBoolean   Method     bool IConvertible.ToBoolean(System.IFormatProvider provider)
ToByte      Method     byte IConvertible.ToByte(System.IFormatProvider provider)
ToChar      Method     char IConvertible.ToChar(System.IFormatProvider provider)
ToDateTime  Method     datetime IConvertible.ToDateTime(System.IFormatProvider provider)
ToDecimal   Method     decimal IConvertible.ToDecimal(System.IFormatProvider provider)
ToDouble    Method     double IConvertible.ToDouble(System.IFormatProvider provider)
ToInt16     Method     int16 IConvertible.ToInt16(System.IFormatProvider provider)
ToInt32     Method     int IConvertible.ToInt32(System.IFormatProvider provider)
ToInt64     Method     long IConvertible.ToInt64(System.IFormatProvider provider)
ToSByte     Method     sbyte IConvertible.ToSByte(System.IFormatProvider provider)
ToSingle    Method     float IConvertible.ToSingle(System.IFormatProvider provider)
ToString    Method     string ToString(), string ToString(string format), string ToString(System.IFormatProvider pr...
ToType      Method     System.Object IConvertible.ToType(type conversionType, System.IFormatProvider provider)
ToUInt16    Method     uint16 IConvertible.ToUInt16(System.IFormatProvider provider)
ToUInt32    Method     uint32 IConvertible.ToUInt32(System.IFormatProvider provider)
ToUInt64    Method     uint64 IConvertible.ToUInt64(System.IFormatProvider provider)

2つのオブジェクト分の実行結果が含まれる。ただしヘッダは共有されている。

2つの実行結果が、同一ヘッダー内で表示されるのは、出力時にフォーマット処理されてるため。
以下のように実行すると、直感的に表示される。

> (1,2) | ForEach-Object {$_ | Get-Member | Out-String}


   TypeName: System.Int32

Name        MemberType Definition
----        ---------- ----------
CompareTo   Method     int CompareTo(System.Object value), int CompareTo(int value), int IComparable.CompareTo(Syst...
Equals      Method     bool Equals(System.Object obj), bool Equals(int obj), bool IEquatable[int].Equals(int other)
GetHashCode Method     int GetHashCode()
GetType     Method     type GetType()
GetTypeCode Method     System.TypeCode GetTypeCode(), System.TypeCode IConvertible.GetTypeCode()
ToBoolean   Method     bool IConvertible.ToBoolean(System.IFormatProvider provider)
ToByte      Method     byte IConvertible.ToByte(System.IFormatProvider provider)
ToChar      Method     char IConvertible.ToChar(System.IFormatProvider provider)
ToDateTime  Method     datetime IConvertible.ToDateTime(System.IFormatProvider provider)
ToDecimal   Method     decimal IConvertible.ToDecimal(System.IFormatProvider provider)
ToDouble    Method     double IConvertible.ToDouble(System.IFormatProvider provider)
ToInt16     Method     int16 IConvertible.ToInt16(System.IFormatProvider provider)
ToInt32     Method     int IConvertible.ToInt32(System.IFormatProvider provider)
ToInt64     Method     long IConvertible.ToInt64(System.IFormatProvider provider)
ToSByte     Method     sbyte IConvertible.ToSByte(System.IFormatProvider provider)
ToSingle    Method     float IConvertible.ToSingle(System.IFormatProvider provider)
ToString    Method     string ToString(), string ToString(string format), string ToString(System.IFormatProvider pr...
ToType      Method     System.Object IConvertible.ToType(type conversionType, System.IFormatProvider provider)
ToUInt16    Method     uint16 IConvertible.ToUInt16(System.IFormatProvider provider)
ToUInt32    Method     uint32 IConvertible.ToUInt32(System.IFormatProvider provider)
ToUInt64    Method     uint64 IConvertible.ToUInt64(System.IFormatProvider provider)





   TypeName: System.Int32

Name        MemberType Definition
----        ---------- ----------
CompareTo   Method     int CompareTo(System.Object value), int CompareTo(int value), int IComparable.CompareTo(Syst...
Equals      Method     bool Equals(System.Object obj), bool Equals(int obj), bool IEquatable[int].Equals(int other)
GetHashCode Method     int GetHashCode()
GetType     Method     type GetType()
GetTypeCode Method     System.TypeCode GetTypeCode(), System.TypeCode IConvertible.GetTypeCode()
ToBoolean   Method     bool IConvertible.ToBoolean(System.IFormatProvider provider)
ToByte      Method     byte IConvertible.ToByte(System.IFormatProvider provider)
ToChar      Method     char IConvertible.ToChar(System.IFormatProvider provider)
ToDateTime  Method     datetime IConvertible.ToDateTime(System.IFormatProvider provider)
ToDecimal   Method     decimal IConvertible.ToDecimal(System.IFormatProvider provider)
ToDouble    Method     double IConvertible.ToDouble(System.IFormatProvider provider)
ToInt16     Method     int16 IConvertible.ToInt16(System.IFormatProvider provider)
ToInt32     Method     int IConvertible.ToInt32(System.IFormatProvider provider)
ToInt64     Method     long IConvertible.ToInt64(System.IFormatProvider provider)
ToSByte     Method     sbyte IConvertible.ToSByte(System.IFormatProvider provider)
ToSingle    Method     float IConvertible.ToSingle(System.IFormatProvider provider)
ToString    Method     string ToString(), string ToString(string format), string ToString(System.IFormatProvider pr...
ToType      Method     System.Object IConvertible.ToType(type conversionType, System.IFormatProvider provider)
ToUInt16    Method     uint16 IConvertible.ToUInt16(System.IFormatProvider provider)
ToUInt32    Method     uint32 IConvertible.ToUInt32(System.IFormatProvider provider)
ToUInt64    Method     uint64 IConvertible.ToUInt64(System.IFormatProvider provider)

write-hostの出力はオブジェクトでないので、パイプで処理されない

クリックで動作メモ表示

> Write-Host "hoge" | Get-Member
hoge
Get-Member : Get-Member コマンドレットにオブジェクトを指定する必要があります。
発生場所 行:1 文字:21
+ Write-Host "hoge" | Get-Member
+                     ~~~~~~~~~~
    + CategoryInfo          : CloseError: (:) [Get-Member]、InvalidOperationException
    + FullyQualifiedErrorId : NoObjectInGetMember,Microsoft.PowerShell.Commands.GetMemberCommand

> Write-Host "hoge" | ForEach-Object {write-host "fuga"; $_.gettype()}
hoge

foreach-objectとforeachステートメントは実行方法が異なる。

foreach-objectは1エントリづつ、foreachはメモリに全エントリため込み後に一気に処理
PowerShellの落とし穴！ForEach-Objectとforeachは違う？ | チェシャわら