lonely_integer.sh

 #!/usr/bin/env bash
 
 #this is the Lonely Integer challenge from HackerRank
 
 declare -a numbers;
 control_string="%d\\n";
 
 read count || [ -n "$count" ];
 
 while read number || [ -n "$number" ]; do
     numbers=( "${numbers[@]}" "$number" );
 done
 
 let "count--";
 while [ "$count" -gt 0 ]; do
     let "count--";
     control_string="${control_string}%d\\n";
 done
 
 var=$( echo "${numbers[@]}" )
 
 printf $control_string $var | uniq -c | sed 's/^ *//;s/ *$//' | grep -P ^1 | awk '{print $2}' | sort | uniq -c | sed 's/^ *//;s/ *$//' | awk '{if($1==1) print $2}'