What are the PowerShell equivalents of Bash’s && and || operators?

Update: && and || have finally come to PowerShell (Core), namely in v7, termed pipeline-chain operators; see this answer for details.

Many years after the question was first asked, let me summarize the behavior of Windows PowerShell, whose latest and final version is v5.1:

• Bash’s / cmd‘s && and || control operators have NO PowerShell equivalents, and since you cannot define custom operators in PowerShell, there are no good workarounds:

  • Use separate commands (on separate lines or separated with ;), and explicitly test the success status of each command via automatic $? variable, e.g.:

    # Equivalent of &&
    command1 -arg1 -arg2; if ($?) { command2 -arg1 }
    
    # Equivalent of ||
    command1 -arg1 -arg2; if (-not $?) { command2 -arg1 } 
    

  • Better alternative for external programs, using the automatic $LASTEXITCODE variable; this is preferable, because $? in Windows PowerShell can yield false negatives (no longer in PowerShell (Core) 7.2+), if a 2> redirection is involved – see this answer:

    # Equivalent of &&
    command1 -arg1 -arg2; if ($LASTEXITCODE -eq 0) { command2 -arg1 }
    
    # Equivalent of ||
    command1 -arg1 -arg2; if ($LASTEXITCODE -ne 0) { command2 -arg1 } 
    

  • See below for why PowerShell’s -and and -or are generally not a solution.

• [Since implemented in PowerShell (Core) 7+] There was talk about adding them a while back, but it seemingly never made the top of the list.

  • Now that PowerShell has gone open-source, an issue has been opened on GitHub.
  • The tokens && and || are currently reserved for future use in PowerShell, so there’s hope that the same syntax as in Bash can be implemented.
    (As of PSv5.1, attempting something like 1 && 1 yields error message The token '&&' is not a valid statement separator in this version.)

Why PowerShell’s -and and -or are no substitute for && and ||:

Bash‘s control operators && (short-circuiting logical AND) and || (short-circuiting logical OR) implicitly check the success status of commands by their exit codes, without interfering with their output streams; e.g.:

ls / nosuchfile && echo 'ok'

Whatever ls outputs — both stdout output (the files in /) and stderr output (the error message from attempting to access non-existent file nosuchfile) — is passed through, but && checks the (invisible) exit code of the ls command to decide if the echo command – the RHS of the && control operator – should be executed.

ls reports exit code 1 in this case, signaling failure — because file nosuchfile doesn’t exist — so && decides that ls failed and, by applying short-circuiting, decides that the echo command need not be executed.
Note that it is exit code 0 that signals success in the world of cmd.exe and bash, whereas any nonzero exit code indicates failure.

In other words: Bash’s && and || operate completely independently of the commands’ output and only act on the success status of the commands.

PowerShell’s -and and -or, by contrast, act only on the commands’ standard (success) output, consume it and then output only the Boolean result of the operation; e.g.:

(Get-ChildItem \, nosuchfile) -and 'ok'

The above:

• uses and consumes the success (standard) output — the listing of \ — and interprets it as a Boolean; a non-empty input collection is considered $true in a Boolean context, so if there’s at least one entry, the expression evaluates to $true.

  • However, the error information resulting from nonexistent file nosuchfile is passed through, because errors are sent to a separate stream.

• Given that Get-ChildItem \, nosuchfile returns non-empty success output, the LHS evaluated to $true, so -and also evaluates the RHS, 'ok', but, again, consumes its output and interprets it as a Boolean, which, as a nonempty string, also evaluates to $true.

• Thus, the overall result of the -and expression is $true, which is (the only success) output.

The net effect is:

• The success output from both sides of the -and expression is consumed during evaluation and therefore effectively hidden.

• The expression’s only (success) output is its Boolean result, which is $true in this case (which renders as True in the terminal).