Backslash in Prometheus label value does not work with dashboard variable

[Mario-Hofstaetter]

What happened:
A prometheus label value containing a backlash \ causes an error when using the value via grafana dashboard variable. Example: logfile="C:\test\logfile.txt"

What you expected to happen:
There should be some way to make it work?

How to reproduce it (as minimally and precisely as possible):

• Have a prometheus metric, with some label with a value containing a backlash, e.g. backslashtest{logfile="C:\test\logfile.txt"} , easiest created by textfile collector.
• Create a dashboard variable Name=logfile, Type=Query, Datasource=Prometheus, Query=label_values(backslashtest, logfile), this gives:
  
• Try to query the metric using this variable, I got no working solution.

backslashtest{logfile="$logfile"}

or

backslashtest{logfile=~"$logfile"}

yields:

"1:23: parse error: unknown escape sequence U+006C 'l'"

I tried all the advanced-variable-format-options, neither worked.

backslashtest{logfile="${logfile:regex}"}

yields "1:23: parse error: unknown escape sequence U+002E '.'"

The only one that does not throw an error is backslashtest{logfile="${logfile:percentencode}"} but Prometheus returns no data for this.

Using the regex Operator =~ makes no difference:

backslashtest{logfile=~"${logfile:regex}"}
backslashtest{logfile=~"${logfile:raw}"}
[...]

Only this works: backslashtest{logfile="C:\\test\\logfile.txt"}

Is there a way to use the variable?

Anything else we need to know?:

Query-Inspector:

{
  "response": {
    "status": "error",
    "errorType": "bad_data",
    "error": "1:24: parse error: unknown escape sequence U+006C 'l'",
    "message": "1:24: parse error: unknown escape sequence U+006C 'l'"
  }
}

• This issues for example arises because Windows filepaths use backlash as seperator, the metric source in my case is grop_exporter
• The raw exporter text actually escapes the backlash backslashtest{logfile="C:\\test\\logfile.txt"}
• When querying in prometheus graph, it needs to be escaped as well

Related?: #10555 #20869

Environment:

• Grafana version: v6.7.3 and v7.0.0-beta3 (2169fc1a3f)
• Data source type & version: Prometheus 2.18.1
• OS Grafana is installed on: Windows 10 1909
• User OS & Browser: Windows 10 1909 , Firefox 75

[Mario-Hofstaetter]

Workaround

If anyone lands here via google, I was able to workaround this PAIN by substituting \ with / directly in grok_exporter using the gsub function like so:

  labels:
    logfile: '{{gsub .logfile "\\\\" "/"}}'

so backslashtest{logfile="C:/test/logfile.txt"} works just fine in grafana 🎉

I dunno if prometheus relabeling is able to do this, the docs there did not look that promising on first sight.

[torkelo]

backslashtest{logfile=~"${logfile}"}

Should work as it will use the prometheus specific regex escaping logic.

[Mario-Hofstaetter]

Are you able to reproduce?
Slightly extended original post, it is happening with v6.7.3 and v7.0.0-beta3

The issue does not appear when using Loki, if using promtail on Windows the logfile label also contains the backslash, it is working fine with the =~ operator.

[aocenas]

Seems like this may be a duplicate of #20869

[ivanahuckova]

Closed by #26205