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Get specific output from grep

I am trying to get a specific output using grep but I am unable to do so. Here is my grep command :

crictl inspect 47aaecb541688accf37840108cc0d19b39b84f8337740edf2ca7e5e81a24328e | grep "io.kubernetes.pod.namespace"

The output of the above command is "io.kubernetes.pod.namespace": "kube-system",

I even tried crictl inspect 47aaecb541688accf37840108cc0d19b39b84f8337740edf2ca7e5e81a24328e | grep -Po '(?<="io.kubernetes.pod.namespace": ").*' but the output i got is kube-system",

I just want the value i.e just kube-system

How do I modify my grep command. Thanks for the help

Solution

  • Using grep

    We need to make just one small change to the grep -P command. Your command was:

    $ echo '"io.kubernetes.pod.namespace": "kube-system",' | grep  -Po '(?<="io.kubernetes.pod.namespace": ").*'
kube-system",

    We just need to replace .* (which matches everything to the end of the line) with [^"]* with matches everything up to but not including the first ":

    $ echo '"io.kubernetes.pod.namespace": "kube-system",' | grep  -Po '(?<="io.kubernetes.pod.namespace": ")[^"]*'
kube-system

    Or, using your crictl command:

    crictl inspect 47aaecb541688accf37840108cc0d19b39b84f8337740edf2ca7e5e81a24328e | grep  -Po '(?<="io.kubernetes.pod.namespace": ")[^"]*'

    Using sed

    $ echo '"io.kubernetes.pod.namespace": "kube-system",' | sed -n '/"io.kubernetes.pod.namespace"/{s/.*": "//; s/".*//p}'
kube-system

    How it works:

    • -n tells sed not to print unless we explicitly ask it to.

    • /"io.kubernetes.pod.namespace"/{...} selects only those lines that contain "io.kubernetes.pod.namespace" and performs the commands in braces on them.

    • s/.*": "// removes everything from the beginning of the line to the last occurrence of ": ".

    • s/".*//p removes everything from the first remaining " to the end of the line and prints the result.