count repeated id numbers in a file with passwd format

countpswd.sh

#!/bin/bash
# check parameters
if [ $# -eq 1 ]; then

	linecount=$(cat $1 | wc -l)

	echo "the file contains" $linecount "lines"

	x=1
	#fist loop over every line for part A of the comparison
	while [ $x -le $linecount ]; do
	  
	  	line=$(tail -n $x $1  | head -n 1)
		name=$(echo $line | cut -d : -f 1)
		uid=$(echo $line | cut -d : -f 3)
		y=1
		count=0
		
		#second loop over every line for part B of the comparison
		while [ $y -le $linecount ]; do
	  		
		  	line1=$(tail -n $y $1  | head -n 1)
			uid1=$(echo $line1 | cut -d : -f 3)
			
			#compares uids, if they are equal, it ++, since the count starts at 0,
			#even if it appears only once it will not oversum. 
			if [ $uid -eq $uid1 ]; then
				count=$(($count + 1))
			fi

		  	y=$(( $y + 1 ))

		done
		#outputs the line into exit.txt, take into consideration that it will not
		#rewrite the file, only append to it.
		echo $name $count >> exit.txt

	  	x=$(( $x + 1 ))
	done

else
	echo "wrong parameters"
fi