'kubectl patch' works on Linux Bash but no

Question

The following command works fine on Ubuntu bash:

kubectl patch deployment wapi-backend-d1 --patch '{"spec": {"template": {"metadata": {"labels": {"date": "test"}}}}}'

The same command does not work in Windows Powershell Console (ISE).

The error is:

kubectl : Error from server (BadRequest): invalid character 's' looking for beginning of object key string
At line:1 char:1
+ kubectl patch deployment wapi-backend-d1 --patch '{"spec": {"template ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (Error from serv...ject key string:String) [], RemoteException
    + FullyQualifiedErrorId : NativeCommandError

The powershell console version is:

PS > $PSVersionTable

Name                           Value                                                                                                                                                                                                                             
----                           -----                                                                                                                                                                                                                             
PSVersion                      5.1.14409.1005                                                                                                                                                                                                                    
PSEdition                      Desktop                                                                                                                                                                                                                           
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}                                                                                                                                                                                                           
BuildVersion                   10.0.14409.1005                                                                                                                                                                                                                   
CLRVersion                     4.0.30319.42000                                                                                                                                                                                                                   
WSManStackVersion              3.0                                                                                                                                                                                                                               
PSRemotingProtocolVersion      2.3                                                                                                                                                                                                                               
SerializationVersion           1.1.0.1            

I have tried the command with a different patched value too as I saw somebody write that patch may fail if it is already applied.

The path /spec/template/metadata/labels/date indeed exists in the deployment's yaml, so that isn't a problem either.

I presume that it might have something to do with kubectl working differently in Powershell in relation to quotes, but could not find a way to make it work.

I have tried

kubectl patch deployment wapi-backend-d1 --patch "{\"spec\": {\"template\": {\"metadata\": {\"labels\": {\"date\": \"test123\"}}}}}"

But that results in

Error from server (NotFound): deployments.extensions "spec\\: {\\template\\: {\\metadata\\: {\\labels\\: {\\date\\: \\test123\\}}}}}" not found

What should be the command on Powershell?

Answer 1

For detailed and very useful background, see the answer by mklement0

After much frustration, I have decided to list all variants of quote escaping that I've tried, and came up with one more, which suddenly worked! So, sharing it here:

kubectl patch deployment wapi-backend-d1 --patch '{\"spec\": {\"template\": {\"metadata\": {\"labels\": {\"date\": \"test123\"}}}}}'

This is how to use kubectl patch with Powershell

Also, of note: I was actually trying to patch it with a timestamp to trigger a rolling update without changing tags of container images (so set image would not help me).

When you try to put your JSON into a variable and then call kubectl patch with a variable, you get into trouble with escaping again. This is what I ended up with:

$patchRequest = @{
    spec = @{
        template = @{
            metadata = @{
                labels = @{
                    date = ((((Get-Date -Format o)).replace(':','-').replace('+','_')))
                }
            }
        }
    }
}
$patchJson = ((ConvertTo-Json -InputObject $patchRequest -Compress -Depth 10))
$patchJson = $patchJson.replace('"','\"')
kubectl patch deployment wapi-backend-d1 --patch $patchJson

Answer 2

You've found the right solution in your own answer, but let me try to break it down conceptually:

Embedding " (double quotes) in string arguments passed to external programs:

• (a) First - sensibly and unavoidably - you need to satisfy PowerShell's syntax requirements with respect to embedding " chars. in quoted strings.

• (b) Then - and this step shouldn't be necessary - you need to \-escape embedded " chars. that you want external programs to see.

  • This is a longstanding, irksome bug that is unlikely to be fixed, however, as long as backward compatibility must be maintained; see this GitHub issue.

Re (a), you have the following options:

• '...'-quoting (single-quoting), inside of which you can use " as-is:

  • '{ "spec": "none" }'
  • Everything inside '...' is taken literally - no expansion (interpolation) takes place.

• "..."-quoting (double-quoting), inside of which you can use `" or "" to embed " chars:

  • "{ `"spec`": `"none`" }" - ` is PowerShell's general escape char.
  • "{ ""spec"": ""none"" }" - "-specific escaping (doubling)
  • The content of "..." is subject to expansion (interpolation), meaning that you can reference variables ($var) or subexpressions ($(1 + 2)) inside such strings, which PowerShell replaces with their values - see this answer for more about PowerShell's expandable strings.

If you're passing such a string to other PowerShell commands (cmdlets, functions, or scripts), no further action is needed; e.g.:

PS> Write-Output '3" of rain'
3" of rain

Re (b) - i.e. to pass such strings to external programs - you additionally need to \-escape the embedded " chars.:

• Applying manual escaping to the examples above:

  • '{ \"spec\": \"none\" }'
  • "{ \`"spec\`": \`"none\`" }"
  • "{ \""spec\"": \""none\"" }"

• Applying the escaping programmatically to a preexisting string:

  • $str = '3" of rain'; $escapedStr = $str -replace '"', '\"'

• That is, for an external program to ultimately see literal value 3" of rain, you must pass literal value 3\" of rain from PowerShell. This \-escaping is something that PowerShell, as a shell, should do automatically behind the scenes, but currently doesn't.

• There's an additional bug in Windows PowerShell - since fixed in PowerShell Core - that mishandles strings with unbalanced embedded " chars. if a " is part of the first word:

  • E.g., the above techniques do NOT work with literal values such as 3" of rain; that is, escaping this as '3\" of rain' does not work as expected - instead, you must use the following monstrosity: `"3\`" of rain`", which is technically a series of separate, unquoted arguments, which means that (a) multiple spaces between the words of the strings aren't supported (they are collapsed to a single space) and (b) PowerShell metacharacters such as & < > $ & | @ { must be individually `-escaped.
  • Note that the bug surfaces only if the " is part of the first word in the value, and only if that first word is not preceded by whitespace (though arguments with leading whitespace are rarely useful); e.g., '3 \" of rain' would again work, because the unbalanced " is not part of the first word.

E.g.:

# Using choice.exe as a sample external program to pass a string to.
# choice.exe echoes the string it receives via /m as the prompt message.
PS> choice /m '{ \"spec\": \"none\" }' /d Y /t 0
{ "spec": "none" } [Y,N]?Y