PowerShell - How to achieve this logic as in bash command line { A ; { B && C ;} ;}

Question

I am trying to achieve a specific logic in PowerShell 1-liner that is similar to the following bash command:

{ $another_command_group ;} && { A ; { B && C ;} ;} && { $another_command_group ;}

{ A ; { B && C ;} ;}

The logic of this command is as follows:

1. A=0, B=0, C=0, then it will execute nothing, and this Command Group will return a 0
2. A=0, B=0, C=1, then it will execute nothing, and this Command Group will return a 0
3. A=0, B=1, C=0, then it will execute Command B only, and this Command Group will return a 0
4. A=0, B=1, C=1, then it will execute Command B and Command C, and this Command Group will return a 1
5. A=1, B=0, C=0, then it will execute Command A only, and this Command Group will return a 0
6. A=1, B=0, C=1, then it will execute Command A only, and this Command Group will return a 0
7. A=1, B=1, C=0, then it will execute Command A and Command B, and this Command Group will return a 0
8. A=1, B=1, C=1, then it will execute All Command A, B, C, and this Command Group will return a 1

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PowerShell version: 7.26

OS: Windows

What I already tried:

• ( A ; ( B && C ) )

  Not Working.

| Missing closing ')' in expression.

• A ; ( B && C )

  Worked though, but apparently this is not good enough, because I need the Parentheses () to make them a (group) to stick with other (group)s with AND &&

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I am having trouble finding a one-liner Command to replicate this logic in PowerShell. I would greatly appreciate any suggestions or solutions.

Answer 1

• A single pipeline chain, i.e. two or more possibly pipeline-connected commands connected via && or ||, the pipeline-chain operators needs no enclosure - except situationally in (...), the grouping operator if clarifying precedence is necessary.

  • For instance, { B && C ;} in your Bash code can be represented as B && C, or, if needed for precedence clarification, (B && C) (note that, unlike in Bash, (...) does not create a subshell in PowerShell).

• To execute multiple statements (a pipeline chain being one example of a statement) as a group, enclose them in a script block, { ... } and also call that block with &, the call operator or, if needed, for PowerShell code, with ., the dot-sourcing operator.

  • That is, { ... } alone does not result in execution - it just defines a reusable piece of PowerShell code that must be called on demand.

  • Also, unlike in Bash, the last statement inside { ... } need not be ;-terminated; ; need only be placed between statements.

  • Unfortunately, unlike in Bash, a script-block call does not preserve the success status of the last command executed inside of it, which in turn means that script-block calls can not meaningfully participate in a pipeline chain, because they invariably signal success.

  • This applies analogously to script files (*.ps1) as well, which, however, can signal success vs. failure via an explicit exit statement, whose use is not an option in a script block (it would exit the script / session as a whole). While return can be used to exit a script block, its purpose - unlike in Bash - is to output data, not to report an exit code.

Therefore, unfortunately, a hypothetical pipeline chain involving script-block calls (the analog of a group command in Bash (POSIX-compatible shells)) must be broken up into multiple statements involving tests of the automatic $LASTEXITCODE variable, which does reflect the exit code of the most recent external-program / script-file call:

& { $another_command_group }
if ($LASTEXITCODE -eq 0) { & { A ; B && C } }
if ($LASTEXITCODE -eq 0) { & { $another_command_group } }

However, as you've discovered yourself - if practical - you can reformulate a script-block call to a logically equivalent single pipeline chain, whose success status does work as expected.

The example you provided is that & { A ; (B && C) } (which itself is the loose analog of command group { A ; { B && C ;} ;} from your Bash command) can be reformulated as a single pipeline chain as follows:

( ( A && B && C ) || ( B && C ) )

The above preserves the success status of whatever program executes last, and can therefore be used as-is in a larger pipeline chain.