Você pode ter problemas para armazenar arquivos grandes na memória, isso é um pouco melhor, pois armazena apenas linhas correspondentes, depois que o sort fez o trabalho pesado de colocar as linhas em ordem.
# Input must be sorted first, then we only need to keep matching lines in memory
# Once we reach a non-matching line we print the lines in memory, prefixed by count
# with awk, variables are unset to begin with so, we can get away without explicitly initializing
{ # S2, S3, S4 are saved field values
if($2 == S2 && $3 == S3 && $4 == S4) {
# if fields 2,3,4 are same as last, save line in array, increment count
line[count++] = $0;
} else {
# new line with fields 2, 3, 4 different
# print stored lines, prefixed by the count
for(i in line) {
print count, line[i];
}
# reset counter and array
count=0;
delete line;
# save this line in array, increment count
line[count++] = $0;
}
# store field values to compare with next line read
S2 = $2; S3 = $3; S4 = $4;
}
END{ # on EOF we still have saved lines in array, print last lines
for(i in line) {
print count, line[i];
}
}
É costume salvar awk
scripts em um arquivo.
Você poderia usar isso ao longo das linhas de sort -k2,4 file | awk -f script
3 ID-fred 4.0 6.0 42.0
3 ID-jacob 4.0 6.0 42.0
3 ID-tessa 4.0 6.0 42.0
2 ID-elsa 5.0 8.0 45.0
2 ID-trudy 5.0 8.0 45.0
1 ID-gerard 6.0 8.0 20.0