Run command line in PowerShell

Question

I know there are lots of posts regarding this, but nothing worked for me.

I am trying to run this command line in PowerShell:

C:/Program Files (x86)/ClamWin/bin/clamd.exe --install

I have this in PowerShell:

&"C:/Program Files (x86)/ClamWin/bin/clamd.exe --install"

But all this does is execute clamd.exe , ignoring the --install parameter

How can I get the full command line to run?

Answer 1

Josef Z's comment on the question provides the solution:

& "C:/Program Files (x86)/ClamWin/bin/clamd.exe" --install # double-quoted exe path

or, given that the executable path is a literal (contains no variable references or subexpressions):

& 'C:/Program Files (x86)/ClamWin/bin/clamd.exe' --install # single-quoted exe path

^{As for why your own solution attempt failed: The call operator & expects only a command name/path as an argument, not a full command line .
Invoke-Expression accepts an entire command line, but that complicates things further and can be a security risk .}

As for why this is the solution:

• The need for quoting stands to reason: you need to tell PowerShell that C:/Program Files (x86)/ClamWin/bin/clamd.exe is a single token (path), despite containing embedded spaces .

• & , the so-called call operator , is needed, because PowerShell has two fundamental parsing modes :

  • argument mode , which works like a traditional shell , where the first token is a command name, with subsequent tokens representing the arguments, which only require quoting if they contain shell metacharacters (chars. with special meaning to PowerShell, such as spaces to separate tokens);
    that is why --install need not , but can be quoted (PowerShell will simply remove the quotes for you before passing the argument to the target executable.)

  • expression mode , which works like expressions in programming languages .

PowerShell decides based on a statement's first token what parsing mode to apply:

If the first token is a quoted string - which we need here due to the embedded spaces in the executable path - or a variable reference (eg, $var ... ), PowerShell parses in expression mode by default .
A quoted string or a variable reference as an expression would simply output the string / variable value.

However, given that we want to execute the executable whose path is stored in a quoted string, we need to force argument mode , which is what the & operator ensures .

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Generally, it's important to understand that PowerShell performs nontrivial pre-processing of the command line before the target executable is invoked, so what the command line looks like in PowerShell code is generally not directly what the target executable sees.

• If you reference a PowerShell variable on the command line and that variable contains embedded spaces, PowerShell will implicitly enclose the variable's value in double quotes before passing it on - this is discussed in this answer to the linked question.

• PowerShell's metacharacters differ from that of cmd.exe and are more numerous (notably, , has special meaning in PowerShell (array constructor), but not cmd.exe - see this answer ).

• To simplify reuse of existing, cmd.exe -based command lines, PowerShell v3 introduced the special stop-parsing symbol , --% , which turns off PowerShell's normal parsing of the remainder of the command line and only interpolates cmd.exe -style environment-variable references (eg, %USERNAME% ).