Bash Function return values in if ...; then statement

Question

I'm in the process to enable the firewall on a VM. Initially the firewall is in a masked state. I use two functions

function status_firewall() {
  RET_VAL=" "
  STATUS=$(systemctl status firewalld)
  MASKED=$(grep -e "masked" <<< $STATUS)
  M_RET=$?

  DEAD=$(grep -e "dead" <<< $STATUS)
  D_RET=$?
  logging "M_RET and D_RET: $M_RET, $D_RET"
  if [ "${M_RET}" -eq "0" ]; then
    RET_VAL=1
  elif [ "${D_RET}" -eq "0" ]; then
    RET_VAL=2
  else
    RET_VAL=0
  fi
  echo ${RET_VAL}
}

echo statement prints value "1" if firewall is masked

function check_firewall() {
  FIREWALL=$(status_firewall)
  logging "Firewall status in check_firewall: ${FIREWALL}"
  if [ "$(status_firewall)" -eq "0" ]; then
    logging "Firewalld service already running"
    RET_VAL=0
  elif [ "$(status_firewall)" -eq "1" ]; then
     ...
  elif
     ...
  fi

I get the correct MASKED and DEAD status value (0, 0) status_firewall() { ... } However, when checking for the return values in check_firewall() { .. } I get the following integer error: integer expression expected

When checking the return value in: check_firewall() it lists: Firewall status: ● firewalld.service Loaded: masked (/dev/null) Active: inactive (dead)

How come the first function supposedly returns value "1" but in the second function it lists the return value as the output of the command: systemctl status firewalld

None of your functions use return values. They just write to stdout. — melpomene
– melpomene, Commented Apr 24, 2019 at 15:32
Change the script to use return codes. return 0 on success and then just if status_firewall; then ... — that other guy
– that other guy, Commented Apr 24, 2019 at 15:39

Gordon Davisson · Accepted Answer · 2019-04-24 17:28:47Z

6

First, simplify status_firewall by using return values instead of writing to standard output, and use pattern matching in a case statement instead of calling grep.

status_firewall() {
    status=$(systemctl status firewalld)
    case $status in
        *masked*) rv=1 ;;
        *dead*)   rv=2 ;;
        *) rv=0 ;;
    esac
    return $rv
}

Then check_firewall is just a matter of examining the exit status of status_firewall.

check_firewall() {
  status_firewall
  case $? in
    0) logging "Firewalld service already running" ;;
    1) ... ;;
    2) ... ;;
  esac
}

In fact, you can do away with status_firewall altogether:

check_firewall() {
  case $(systemctl status firewalld) in
    *masked*) ... ;;
    *dead*) ... ;;
    *) logging "Firewalld service already running" ;;
  esac
}

edited Apr 24, 2019 at 17:28

Gordon Davisson

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answered Apr 24, 2019 at 17:18

chepner

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1 Comment

user2872898 Over a year ago

Thank you for the detailed info. That is some very nice code. Shows me I have a long way to go

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