can't print array values in bash

Question

I need to generate ipset rules dynamically. so i created following script and having error try to get the urls from array.

#!/bin/bash

# urlList
allow_SMTP_OUT_URLS=(mtp.sendgrid.net)
allow_HTTP_OUT_URLS=(archive.mariadb.org)
allow_HTTPS_OUT_URLS=(ppa.launchpad.net repo.mongodb.org www.google.com)
allow_SSH_OUT_URLS=(bitbucket.org)

ipsetNames=(allow_HTTP_OUT allow_HTTPS_OUT allow_SMTP_OUT allow_SSH_OUT)

for ipSET in "${ipsetNames[@]}"
do

   ipset create -exist $ipSET hash:ip timeout 86400 comment family inet

   chkIPSETexsit="$(ipset list -n | grep $ipSET)"

# Check / Adding IPSET rules
   if [ -z "$chkIPSETexsit" ]; then
       echo "$ipSET is empty"
       exit 1
   else
       echo "$ipSET is present. Adding URLs to ipset"

       urlList=$ipSET
       urlList+="_URLS"

       echo "urlList: $urlList"

       echo URLs:   ${(echo $urlList)[@]}
   fi
done

its gives error as bad substitution

allow_HTTP_OUT is present. Adding URLs to ipset
urlList: allow_HTTP_OUT_URLS
/root/salt-cron-scripts/test2.sh: line 30: ${(echo $urlList)[@]}: bad substitution

Any suggestions to correct this please

You've reached the level of data manipulation where bash is no longer appropriate to use. Choose a language with proper data structures. — chepner
– chepner, Commented Nov 28, 2017 at 0:28

PesaThe · Accepted Answer · 2017-11-28 00:57:25Z

2

You can use a nameref declared with declare -n. This gives you a slightly better and more intuitive manipulation than using indirect parameter expansion, such as using: ${urls[@]}, ${urls[0]}, ${urls[5]//a/b} etc.

#!/bin/bash

# urlList
allow_SMTP_OUT_URLS=(mtp.sendgrid.net)
allow_HTTP_OUT_URLS=(archive.mariadb.org)
allow_HTTPS_OUT_URLS=(ppa.launchpad.net repo.mongodb.org www.google.com)
allow_SSH_OUT_URLS=(bitbucket.org)

ipsetNames=(allow_HTTP_OUT allow_HTTPS_OUT allow_SMTP_OUT allow_SSH_OUT)

for ipSET in "${ipsetNames[@]}"
do

   ipset create -exist $ipSET hash:ip timeout 86400 comment family inet

   chkIPSETexsit="$(ipset list -n | grep $ipSET)"

# Check / Adding IPSET rules
   if [ -z "$chkIPSETexsit" ]; then
       echo "$ipSET is empty"
       exit 1
   else
       echo "$ipSET is present. Adding URLs to ipset"

       urlList=${ipSET}_URLS
       echo "urlList: $urlList"
       declare -n urls=$urlList
       echo "URLs: ${urls[@]}"

   fi
done

answered Nov 28, 2017 at 0:57

PesaThe

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1 Comment

Sha Over a year ago

Thank you very much for the explanation it's really helpful.

chepner · Accepted Answer · 2017-11-28 00:31:42Z

You need to use indirect parameter expansion to expand the array named by urlList.

allow_SMTP_OUT_URLS=(mtp.sendgrid.net)
allow_HTTP_OUT_URLS=(archive.mariadb.org)
allow_HTTPS_OUT_URLS=(ppa.launchpad.net repo.mongodb.org www.google.com)
allow_SSH_OUT_URLS=(bitbucket.org)

ipsetNames=(allow_HTTP_OUT allow_HTTPS_OUT allow_SMTP_OUT allow_SSH_OUT)

for ipSET in "${ipsetNames[@]}"
do

   ipset create -exist "$ipSET" hash:ip timeout 86400 comment family inet

   chkIPSETexsit="$(ipset list -n | grep $ipSET)"

   # Check / Adding IPSET rules
   if [ -z "$chkIPSETexsit" ]; then
       echo "$ipSET is empty"
       exit 1
   fi

   echo "$ipSET is present. Adding URLs to ipset"

   urlList=${ipSET}_URLS
   echo "urlList: $urlList"
   urlList=$urlList[@]

   echo "URLs: ${!urlList}"
done

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