Powershell 7: using ampersand (&) in string literals-CodePudding

I'm trying to execute following command in powershell but have no how to escape the ampersand character as this is part of the url

  az rest `
    --method GET `
    --uri ("https://graph.microsoft.com/v1.0/groups?`$count=true&`$filter=startsWith(displayName,'some filter text')&`$select=id,displayName") `
    --headers 'Content-Type=application/json'

As the & character is used to start a new command, it breaks the url and want to execute the remainder.

Is there a way to tell powershell not to do that?

CodePudding user response：

Olaf's answer provides an effective solution; let me add an explanation:

The source of the problem is a confluence of two behaviors:

When calling external programs, PowerShell performs on-demand double-quoting of each argument solely based on whether a given argument value contains spaces - otherwise, the argument is passed unquoted - irrespective of whether or not the value was originally quoted in the PowerShell command (e.g., cmd /c echo ab, cmd /c echo 'ab', and cmd /c echo "ab" all result in unquoted ab getting passed as the last token on the command line PowerShell rebuilds behind the scenes to ultimately use for execution).
The Azure az CLI is implemented as a batch file (az.cmd) and when a batch file is called, it is cmd.exe that parses the arguments given; surprisingly - and arguably inappropriately - it parses them as if the command had been submitted from inside a cmd.exe session.

As a result, if an argument is passed from PowerShell to a batch file that (a) contains no spaces, yet (b) contains cmd.exe metacharacters such as &, the call breaks.

A simple demonstration, using a cmd /c echo call as a stand-in for a call to a batch file:

# !! Breaks, because PowerShell (justifiably) passes *unquoted* a&b
# !! when it rebuilds the command line to invoke behind the scenes.
PS> cmd /c echo 'a&b'
a
'b' is not recognized as an internal or external command,
operable program or batch file.

There are three workarounds:

Use embedded "..." quoting:

# OK, but with a CAVEAT: 
#   Works as of PowerShell 7.2, but arguably *shouldn't*, because
#   PowerShell should automatically *escape* the embedded " chars. as ""
PS> cmd /c echo '"a&b"'
"a&b"

Use --%, the stop-parsing token - but see the bottom section of this answer for the limitations of --% and its associated pitfalls.

# OK, but with a CAVEAT:
#  Requires "..." quoting, but doesn't recognize *PowerShell* variables,
#  also doesn't support single-quoting and line continuation.
PS> cmd /c echo --% "a&b"
 "a&b"

Call via cmd /c and pass a single string encompassing the batch-file call and all its arguments, (ultimately) using cmd.exe's syntax.

# OK (remember, cmd /c echo stands for a call to a batch file, such as az.cmd)
# Inside the single string passed to the outer cmd /c call,
# be sure to use "...", as that is the only quoting cmd.exe understands.
PS> cmd /c 'cmd /c echo "a&b"'
"a&b"

Taking a step back:

Now, wouldn't it be nice if you didn't have to worry about all these things? Especially since you may not know or care if a given CLI - such as az - just so happens to be implemented as a batch file?

As a shell, PowerShell should do its best to relay arguments faithfully behind the scenes, and allow the caller to focus exclusively on satisfying only PowerShell's syntax rules:

Unfortunately, PowerShell has to date (PowerShell 7.2) generally done a very poor job in this regard, irrespective of cmd.exe's quirks - see this answer for a summary.
With respect to cmd.exe's (batch-file call) quirks, PowerShell could predictably compensate for them in a future version - but it looks like that isn't going to happen, unfortunately; see GitHub issue #15143.

CodePudding user response：

I don't have access to an Azure tennant right now to test and I actually don't have experiences with the Azure CLI in general but I'd expect this to work:

az rest `
    --method GET `
    --uri 'https://graph.microsoft.com/v1.0/groups?$count=true&$filter=startsWith(displayName,some filter text)&$select=id,displayName' `
    --headers 'Content-Type=application/json'

or this:

az rest --method GET --headers "Content-Type=application/json" `
    --% --uri "https://graph.microsoft.com/v1.0/groups?$count=true&$filter=startsWith(displayName,some filter text)&$select=id,displayName"

I only added the backticks for better readability - you may remove them in your actual code.