Bitten by double quotes while passing arguments to a bash function

So I wrote a script to setup some networks. The script is not that important for this article; in fact I do not like said script anymore and will replace it with some wholesome ansible playbooks. What matters in it is this bit of code:

So the script is called nething.sh and kinda looks like this:

#! /bin/bash
# Populate openstack networks

HEAD_NODE_IPADDRESS="10.0.0.30"
COMPUTE_NOTE=$HEAD_NODE_IP_ADDRESS
SEC_GROUP="custom-1"
NET_TYPE="flat"
PHYSICAL_NETWORK_DEFAULT="extnet"
NET_NAME="public"
SUBNET_NAME="subnet-${NET_NAME}"
CIDR="10.0.0.0/24"
DNS_NAMESERVER1="10.0.0.10"
GATEWAY_IP="10.0.0.2"
DHCP_ALLOCATION_START="10.0.0.249"
DHCP_ALLOCATION_END="10.0.0.254"

# Boring things here
function CreateNetwork
{
   net_name=$1
   net_id=$2          # vlan tag, segmentation ID
   net_type=$3
   subnet_name=$4
   subnet_range=$5    # Subnet is not necessarily as wide as its parent network
   gateway=$6
   subnet_dhcp_start=$7
   subnet_dhcp_end=$8
   nameserver=$9
   physical_net=$10

   if [[ ${net_id} == "EXT" ]]; then
      openstack network create --provider-network-type ${net_type} \
[...]
}

# Public Network
   CreateNetwork \
      $NET_NAME \
      "EXT" \
      $NET_TYPE \
      $SUBNET_NAME \
      $CIDR \
      $GATEWAY_IP \
      $DHCP_ALLOCATION_START \
      $DHCP_ALLOCATION_END \
      $DNS_NAMESERVER1 \
      $PHYSICAL_NETWORK_DEFAULT

which defines a few constants on the top and then pass them to a function in the end of the script.

Every time I ran the script, it kept crashing and burning, and I did not know why. So I ran the script as bash -x nething.sh so it would spit out each line/variable as it passed through them. Here is how the output looks like:

+ HEAD_NODE_IPADDRESS=10.0.0.30
+ COMPUTE_NOTE=
+ SEC_GROUP=custom-1
+ NET_TYPE=flat
+ PHYSICAL_NETWORK_DEFAULT=extnet
+ NET_NAME=public
+ SUBNET_NAME=public_subnet
+ CIDR=10.0.0.0/24
+ DNS_NAMESERVER1=10.0.0.10
+ GATEWAY_IP=10.0.0.2
+ DHCP_ALLOCATION_START=10.0.0.249
+ DHCP_ALLOCATION_END=10.0.0.254
+ CreateNetwork public BLANK flat public_subnet 10.0.0.0/24 ' '
+ net_name=public
+ net_id=BLANK
+ net_type=flat
+ subnet_name=public_subnet
+ subnet_range=10.0.0.0/24
+ gateway=' '
+ subnet_dhcp_start=
+ subnet_dhcp_end=
+ nameserver=
+ physical_net=public0
+ [[ BLANK == \E\X\T ]]
+ [[ BLANK == \B\L\A\N\K ]]

The line starting with CreateNetwork public BLANK means we are going to the function CreateNetwork(); what is come after is a list of the local variables inside the function which were populated by the function call. The [[ BLANK == \E\X\T ]] is how an if test looks like under the -x option, specifically

if [[ ${net_id} == "EXT" ]]; then

To save time I will spoil the fun: take a look at the gateway variable. Why is it blank? And why every other variable after it is blank? Note that the line

+ CreateNetwork public BLANK flat public_subnet 10.0.0.0/24 ' '

tells us that

• gateway is being passed as ' ' right from the function call.
• No other argument after gateway is being passed.

Why?

The problem is CIDR="10.0.0.0/24", specifically the double quotes. They are expanding the string 10.0.0.0/24 and interpreting the /24 as a character. The solution is to use single quotes, as in

HEAD_NODE_IPADDRESS="10.0.0.30"
COMPUTE_NOTE=$HEAD_NODE_IP_ADDRESS
SEC_GROUP="custom-1"
NET_TYPE="flat"
PHYSICAL_NETWORK_DEFAULT="extnet"
NET_NAME="public"
SUBNET_NAME="${NET_NAME}_subnet"
CIDR='10.0.0.0/24'
DNS_NAMESERVER1="10.0.0.10"
GATEWAY_IP="10.0.0.2"
DHCP_ALLOCATION_START="10.0.0.249"
DHCP_ALLOCATION_END="10.0.0.254"

If we then run that, the strings now behave as expected:

[root@stakola ~(keystone_admin)]# bash -x nething.sh
+ HEAD_NODE_IPADDRESS=10.0.0.30
+ COMPUTE_NOTE=
+ SEC_GROUP=custom-1
+ NET_TYPE=flat
+ PHYSICAL_NETWORK_DEFAULT=extnet
+ NET_NAME=public
+ SUBNET_NAME=public_subnet
+ CIDR=10.0.0.0/24
+ DNS_NAMESERVER1=10.0.0.10
+ GATEWAY_IP=10.0.0.2
+ DHCP_ALLOCATION_START=10.0.0.249
+ DHCP_ALLOCATION_END=10.0.0.254
+ CreateNetwork private 6855 vlan private_subnet 192.168.55.0/24 192.168.55.1 192.
168.55.100 192.168.55.200 10.0.0.10 physnet1
+ net_name=private
+ net_id=6855
+ net_type=vlan
+ subnet_name=private_subnet
+ subnet_range=192.168.55.0/24
+ gateway=192.168.55.1
+ subnet_dhcp_start=192.168.55.100
+ subnet_dhcp_end=192.168.55.200
+ nameserver=10.0.0.10
+ physical_net=private0
+ [[ 6855 == \E\X\T ]]
+ [[ 6855 == \B\L\A\N\K ]]
[...]

Moral of the story: know when to use single and double quotes!