Calculate intron length from gtf

calculate_intron_length_gtf

#!/bin/awk -f

BEGIN{OFS="\t"}
{ start[NR]=$4; 
  end[NR]=$5; 
  strand[NR]=$7; 
  ID[NR]=$11; 
  chr[NR]=$1; 
  ens[NR]=$9; 
  symb[NR]=$10} 

END { 
    for (i=1; i<=NR; i++){
        if(ID[i]==ID[i+1]){ 
            if(strand[i]=="+"){
                intron_start=start[i+1]-1;
                intron_end=end[i]+1;
                print chr[i], 
                      intron_end, 
                      intron_start,
                      "intron",
                      strand[i], 
                      ens[i],
                      symb[i], 
                      ID[i]

            }   
            else{
                intron_start=end[i]+1;
                intron_end=start[i+1]-1;
                print chr[i], 
                      intron_start, 
                      intron_end,
                      "intron",
                      strand[i], 
                      ens[i], 
                      symb[i], ID[i]
            }   
        }   
    }   
}

# Example input 
==> mod_ucsc_mm10_ensembl_genes_exons.gtf <==
chr1    mm10_ensGene    exon    134199223       134203590       0.000000        -       .       ENSMUSG00000042429      Adora1  ENSMUST00000086465
chr1    mm10_ensGene    exon    134234015       134234412       0.000000        -       .       ENSMUSG00000042429      Adora1  ENSMUST00000086465
chr1    mm10_ensGene    exon    134235228       134235431       0.000000        -       .       ENSMUSG00000042429      Adora1  ENSMUST00000086465
chr1    mm10_ensGene    exon    134199223       134203590       0.000000        -       .       ENSMUSG00000042429      Adora1  ENSMUST00000038191
chr1    mm10_ensGene    exon    134234015       134235427       0.000000        -       .       ENSMUSG00000042429      Adora1  ENSMUST00000038191
chr1    mm10_ensGene    exon    134199223       134201713       0.000000        -       .       ENSMUSG00000042429      Adora1  ENSMUST00000169927
chr1    mm10_ensGene    exon    134202065       134203590       0.000000        -       .       ENSMUSG00000042429      Adora1  ENSMUST00000169927
chr1    mm10_ensGene    exon    134234015       134234578       0.000000        -       .       ENSMUSG00000042429      Adora1  ENSMUST00000169927
chr1    mm10_ensGene    exon    8361475 8363633 0.000000        -       .       ENSMUSG00000025909      Sntg1   ENSMUST00000140295
chr1    mm10_ensGene    exon    8414203 8414313 0.000000        -       .       ENSMUSG00000025909      Sntg1   ENSMUST00000140295