Shell Programming and Scripting

pesky awk-s - don't flush output  unless you explicitly close the pipped cmd
awk 'NR % 2 {print;next}; {print | "rev";close("rev")}' myfile

# for every EVEN line
!(FNR%2) {
   # initialize a temp var t to an empty string
   t=""
   # temp var 'l' contains the length of the current record/line
   l=length
   # iterate through the current line assigning the reversed chars to 't'
   for(i=1;i<=l;i++) 
      t=substr($0,i,1) t
   # assign the final reversed record/line back to $0
   $0=t
}
# 1 in awk is default/shortcut to 'print' current/$0 record/line
1

awk '{if (NR % 2) {print} else {r="rev" ; print | r; close(r);}; }' input

awk '!(NR%2){for(i=2;i<=NF;i++) $1=$i $1; $0=$1}1' FS= file