bash: combine five lines of input to each line of output

Question

I have a input file as follows:

MB1 00134141 
MB1 12415085 
MB1 13253590
MB1 10598105
MB1 01141484
...
...
MB1 10598105

I want to combine 5 lines and merge it into one line. I want my bash script to process the bash script to produce output as follows:

MB1 00134141 MB1 12415085 MB1 13253590 MB1 10598105 MB1 01141484
...
...
...                                                 

I have written following script and it works but it is slow for file of size 23051 lines. Can I write a better code to make it faster?

#!/bin/bash
file=timing.csv
x=0
while [ $x -lt $(cat $file | wc -l) ]
do
   line=`head -n $x $file | tail -n 1`
   echo -n $line " "
   let "remainder = $x % 5"
   if [ "$remainder" -eq 0 ] 
   then
        echo ""
   fi
   let x=x+1
done
exit 0

I tried to execute the following command but it messes up some numbers.

cat timing_deleted.csv | pr -at5

Answer 1

In pure bash, with no external processes (for speed):

while true; do
  out=()
  for (( i=0; i<5; i++ )); do
    read && out+=( "$REPLY" )
  done
  if (( ${#out[@]} > 0 )); then
    printf '%s ' "${out[@]}"
    echo
  fi
  if (( ${#out[@]} < 5 )); then break; fi
done <input-file >output-file

This correctly handles files where the number of lines is not a multiple of 5.