docs(core): improve run commands in parallel section (#21083)

Co-authored-by: Isaac Mann <isaacplmann@users.noreply.github.com>
Co-authored-by: Altan Stalker <stalkeraltan@gmail.com>

docs/shared/monorepo-ci-github-actions.md

@@ -163,22 +163,30 @@ jobs:
 
       - name: Run commands in parallel
         run: |
+          # initialize an array to store process IDs (PIDs)
           pids=()
+
+          # function to run commands and store the PID
+          function run_command() {
+            local command=$1
+            $command &  # run the command in the background
+            pids+=($!)  # store the PID of the background process
+          }
+
           # list of commands to be run on main has env flag NX_CLOUD_DISTRIBUTED_EXECUTION set to false
-          NX_CLOUD_DISTRIBUTED_EXECUTION=false npx nx-cloud record -- npx nx format:check & pids+=($!)
+          run_command "NX_CLOUD_DISTRIBUTED_EXECUTION=false npx nx-cloud record -- npx nx format:check"
 
           # list of commands to be run on agents
-          npx nx affected -t lint,test,build --parallel=3 & 
+          run_command "npx nx affected -t lint,test,build --parallel=3"
-          pids+=($!)
 
-          # run all commands in parallel and bail if one of them fails
+          # wait for all background processes to finish
           for pid in ${pids[*]}; do
             if ! wait $pid; then
-              exit 1
+              exit 1  # exit with an error status if any process fails
             fi
           done
 
-          exit 0
+          exit 0 # exits with success status if a all processes complete successfully
 
   agents:
     name: Agent ${{ matrix.agent }}