Shell Programming and Scripting

nawk -F'|' '$1==f{c=0;next}{if(c)print r;c=1;r=$0;f=$1}END{if(c)print r}'

#!/usr/bin/ksh

c=false

while IFS='|' read -r f1 fr; do
  [[ $f1 = $f ]] && { c=false; continue; }
  $c && print -r -- $r
  c=true; f=$f1; r="$f1|$fr"
done

$c && print -r -- $r

awk -F\| 'NR==FNR{_[$1]++;next}_[$1]<2' infile infile

awk 'BEGIN { 
  ARGV[ARGC++] = ARGV[ARGC-1]
  FS = "|"
  }
NR == FNR {
  _[$1]++; next
  }
_[$1] < 2' infile

awk -F\| 'END { for (K in k) print r[K] }
k[$1]++ { delete k[$1] } { r[$1] = $0 }
' infile