Kubernetes POD Command and argument

Question

I am learning kubernetes and have the following question related to command and argument syntax for POD.

Are there any specific syntax that we need to follow to write a shell script kind of code in the arguments of a POD? For example

In the following code, how will I know that the while true need to end with a semicolon ; why there is no semi colon after do but after If etc

   while true;
  do
  echo $i;
  if [ $i -eq 5 ];
  then
    echo "Exiting out";
    break;
  fi;
      i=$((i+1));
      sleep "1";
  done

We don't write shell script in the similar way from semicolon prespective so why do we have to do this in POD.

I tried the command in /bin/bash format as well

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: bash
  name: bash
spec:
  containers:
  - image: nginx
    name: nginx
    args:
    - /bin/bash
    - -c
    - >
       for i in 1 2 3 4 5
       do
         echo "Welcome $i times"
       done
    resources: {}
  dnsPolicy: ClusterFirst
  restartPolicy: Always
status: {}

Error with new code

/bin/bash: -c: line 2: syntax error near unexpected token `echo'
/bin/bash: -c: line 2: `  echo "Welcome $i times"'

This has nothing to do with Kubernetes and its commands or argument. Its is the way bash script is written, Eg: while true; do date; sleep 1; done . Notice there is no semicolon after do. — P....
– P...., Commented Apr 14, 2022 at 16:00
Also, IMO it's best to supply any multi-line script via config-maps not directly through the pod's command. — P....
– P...., Commented Apr 14, 2022 at 16:02
@P.... my reference to kube was because of pod where I am writing the script. So what I understood from your explanation is the syntax that I am using is because of the type of shell I am using like /bash Vs /sh ? — James Stan
– James Stan, Commented Apr 14, 2022 at 17:55
yes, the syntax of shell script is defined by type of shell used. — P....
– P...., Commented Apr 14, 2022 at 17:58
@P.... Following is the bash syntax I have now but it still error out args: - /bin/bash - -c - > for i in 1 2 3 4 5 do echo "Welcome $i times" done /bin/bash: -c: line 2: syntax error near unexpected token echo' /bin/bash: -c: line 2: echo "Welcome $i times"' — James Stan
– James Stan, Commented Apr 14, 2022 at 19:26

gohm'c · Accepted Answer · 2022-04-15 04:07:35Z

Are there any specific syntax that we need to follow to write a shell script kind of code in the arguments of a POD?

No, shell syntax is the same across.

...how will I know that the while true need to end with a semicolon

Used | for your text block to be treated like an ordinary shell script:

...
args:
- /bin/bash
- -c
- |
  for i in 1 2 3 4 5
  do
    echo "Welcome $i times"
  done

When you use > your text block is merge into a single line where newline is replaced with white space. Your command become invalid in such case. If you want your command to be a single line, then write them with ; like you would in ordinary terminal. This is shell scripting standard and is not K8s specific.

If you must use >, you need to either add empty line or indented the next line correctly:

apiVersion: v1
kind: Pod
metadata:
  labels:
    run: bash
  name: bash
spec:
  containers:
  - image: nginx
    name: nginx
    args:
    - /bin/bash
    - -c
    - >
      for i in 1 2 3 4 5
        do
          echo "Welcome $i times"
        done
  restartPolicy: Never

kubectl logs bash to see the 5 echos and kubectl delete pod bash to clean-up.

Collectives™ on Stack Overflow

Kubernetes POD Command and argument

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related