Bash while read : output issue

If temp_ip contains the name of a file that you want to read, then use:

done<"$temp_ip"

In your case, it appears that temp_ip is not a file name but contains the actual data that you want. In that case, use:

done<<<"$temp_ip"

Take care that the variable is placed inside double-quotes. That protects the data against the shell's word splitting which would result in the replacement of new line characters with spaces.

More details

In bash, an expression like <"$temp_ip" is called redirection. In this case in means that the while loop will get its standard input from the file called $temp_ip.

The expression <<<"$temp_ip" is called a here string. In this case, it means that the while loop will get its standard input from the data in the variable $temp_ip.

More information on both redirection and here strings in man bash.

Or you can parse the output of your initial command directly:

$mysql --skip-column-names -h $db_address -u $db_user -p$db_passwd $db_name -e "select ip_routeur,code_site from $db_vtiger_table where $db_vtiger_table.ip_routeur NOT IN (select ip from $db_erreur_table) | \
while read ip codesite
do
...
done

If you want to improve the performance and run some of the 5,000 SNMPGETs in parallel, I would recommend using GNU Parallel (here) like this:

$mysql --skip-column-names -h $db_address -u $db_user -p$db_passwd $db_name -e "select ip_routeur,code_site from $db_vtiger_table where $db_vtiger_table.ip_routeur NOT IN (select ip from $db_erreur_table) | parallel -k -j 20 -N 2 sendSNMPGET {1} $snmp_community {2}

The -k will keep the parallel output in order. The -j 20 will run up to 20 SNMPGETs in parallel at a time. The -N 2 means take 2 parameters from the mysql output per job (i.e. ip and codesite). {1} and {2} are your ip and codesite parameters.

http://www.gnu.org/software/parallel/

I propose to not store the result value but use it directly:

while read ip codesite
do
    sendSNMPGET "$ip" "$snmp_community" "$code_site" &
done < <(
  "$mysql" --skip-column-names -h "$db_address" -u "$db_user" -p"$db_passwd" "$db_name" \
         -e "select ip_routeur,code_site from $db_vtiger_table where $db_vtiger_table.ip_routeur NOT IN (select ip from $db_erreur_table);")

This way you start the mysql command in a subshell and use its output as input to the while loop (similar to piping which here also is an option).

But I see some problems with that code: If you really start each sendSNMPGET command in the background, you very quickly will put a massive load on your computer. For each line you read another active background process is started. This can slow down your machine to the point where it is rendered useless.

I propose to not run more than 20 background processes at a time.