I recently was handed responsibility for a script which has array references that are new to me and I could use some help understanding them.
Parts of the config file and script are included. This script collects backups from a jail server of the jails running on that host. Several jail servers are backed up.
In the first config file the collect0_backup_host="host.xxx.net" refers to the jail host.
It is the syntax of collect0_backup_host that throws me. collect0 is translated to
$collect${N} in the script -- this part I understand -- but the _backup-host (variable?)
that is appended to collect0 is confusing me. I've never seen an array defined this way before and could use some useful links or explaination of how this works.
Thanks
thumper
Code:
config file
collect0_backup_host="host.xxx.net"
collect0_jails="host9.xxx.net host1.xxx.net host2.xxx.net host4.xxx.net"
collect0_backups_dir="/backups/"
collect0_remote_user="host_backups"
collect0_private_key_file="/etc/ssh/jail_backups/host_backups"
#
collect1_backup_host="alt-host.xxx.net"
collect1_jails="dumbo.xxx.net mickey.xxx.net"
collect1_backups_dir="/backups/"
collect1_remote_user="snark_backups"
collect1_private_key_file="/etc/ssh/jail_backups/snark_backups"
#
script
backup_host=`eval echo \\$collect${N}_backup_host`
while backup_host do
do-something
done
jails=`eval echo \\$collect${N}_jails`
remote_user=`eval echo \\$collect${N}_remote_user`
if [ ! ${remote_user} ]; then
echo
echo "ERROR: no remote user defined for collecting backups from ${backup_host}"
echo
ERROR_JAILS="${ERROR_JAILS} ${jails}"
# iterate to the set of jail variables
N=$(expr ${N} + 1)
backup_host=`eval echo \\$collect${N}_backup_host`
continue
Last edited by Scott; 09-16-2010 at 05:20 PM..
Reason: Replaced ICODE tags with CODE tags
This is construction that is used if a shell in question does not know arrays. The way it is used in the script that you were handed, is a bit cumbersome. Instead of
eval works like this: first everything after eval is passed as parameter to eval. The shell processes the variable ${N}. The first $ is escaped ( \$ ), so that it is not treated as a special character. So after processing the command eval gets the following string (suppose N=1):
Code:
backup_host=$collect1_backup_host
end then executes this. As a result you would get:
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