Running sh shell in Busybox

user_14758064 0
Viewed 934

Hope all is well. I am stuck with this Pod executing a shell script, using the BusyBox image. The one below works,

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: loop
  name: busybox-loop
spec:
  containers:
  - args:
    - /bin/sh
    - -c
    - |-
      for i in 1 2 3 4 5 6 7 8 9 10; \
      do echo "Welcome $i times"; done
    image: busybox
    name: loop
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Never
status: {}

But this one doesn't works as I am using "- >" as the operator,

apiVersion: v1
kind: Pod
metadata:
  labels:
    run: busybox-loop
  name: busybox-loop
spec:
  containers:
  - image: busybox
    name: busybox-loop
    args:
    - /bin/sh
    - -c
    - >
    - for i in {1..10};
    - do
    - echo ("Welcome $i times");
    - done
  restartPolicy: Never

Is it because the for syntax "for i in {1..10};" will not work on sh shell. As we know we don't have any other shells in Busybox or the "- >" operator is incorrect, I don't think so because it works for other shell scripts.

Also when can use "- |" multiline operator(I hope the term is correct) and "- >" operator. I know this syntax below is easy to use, but the problem is when we use double quotes in the script, the escape sequence confuses and never works.

args: ["-c", "while true; do echo hello; sleep 10;done"]

Appreciate your support.

kubernetes
3 Answers

...But this one doesn't works as I am using "- >" as the operator...

You don't need '-' after '>' in this case, try:

apiVersion: v1
kind: Pod
metadata:
  name: busybox
  labels:
    run: busybox
spec:
  containers:
  - name: busybox
    image: busybox
    args:
    - ash
    - -c
    - >
      for i in 1 2 3 4 5 6 7 8 9 10;
      do
      echo "hello";
      done

kubectl logs pod busybox will print hello 10 times.

user_147047990

I think you can use this command to create the pod:

$ kubectl run busybox --image=busybox --dry-run=client -o yaml --command -- /bin/sh -c "for i in {1..10}; do echo 'Welcome $i times'; done" | kubectl apply -f -
  pod/busybox created

$ kubectl logs busybox                                                                                                                                          
  Welcome 10 times

Note that you can take a look into YAML created by the dry run command as well.

apiVersion: v1
kind: Pod
metadata:
  labels:
    run: busybox
  name: busybox
spec:
  containers:
  - image: busybox
    command:
      - /bin/sh
      - -c
      - for i in {1..10}; do echo 'Welcome $i times'; done
user_43343760

Brace expansion in for loop is not supported by ash shell. One more solution here can be replacing it with seq command and update formatting like this:

spec:
  containers:
  - image: busybox
    name: busybox-loop
    args:
    - /bin/sh 
    - -c
    - >
      for i in `seq 1 10`;
      do echo "Welcome $i times";
      done
  restartPolicy: Never

It doesn't matter in this case which operator to use - - | or - >, both will work fine.

user_177950060
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