extract chromosome names from blast output

Question

[Ric]

HI, I ran blastn with blastall and I just wondering how could I extract each chromosome alignment to a separate file i.e. I have 10 chromosomes and I would like to get 10 files?

Here is my blastn output file example:
BLASTN 2.2.22 [Sep-27-2009]


Reference: Altschul, Stephen F., Thomas L. Madden, Alejandro A. Schaffer, 
Jinghui Zhang, Zheng Zhang, Webb Miller, and David J. Lipman (1997), 
"Gapped BLAST and PSI-BLAST: a new generation of protein database search
programs",  Nucleic Acids Res. 25:3389-3402.

Query= tig00022194
         (464,128 letters)

Database: musa_acuminata_v2_pseudochromosome-1-11.fasta.clean 
           11 sequences; 397,008,016 total letters

Searching..................................................done



                                                                 Score    E
Sequences producing significant alignments:                      (bits) Value

chr08                                                                8.185e+04   0.0  
chr05                                                                1.171e+04   0.0  
chr11                                                                1.080e+04   0.0  
chr02                                                                1.077e+04   0.0  
chr09                                                                1.037e+04   0.0  
chr03                                                                1.028e+04   0.0  
chr07                                                                1.002e+04   0.0  
chr06                                                                9932   0.0  
chr10                                                                9874   0.0  
chr01                                                                9846   0.0  
chr04                                                                9787   0.0  

>chr08
          Length = 44889171

 Score = 8.185e+04 bits (41289), Expect = 0.0
 Identities = 41909/42103 (99%), Gaps = 57/42103 (0%)
 Strand = Plus / Minus


Query: 376639   ctctccctctccacctcagagcaggcctggagttttgaggagcgtcgtcgcaaccctgct 376698
                |||| |||||||||||||||||||||||||||||| ||||||||||||||||||||||||
Sbjct: 21232377 ctcttcctctccacctcagagcaggcctggagttt-gaggagcgtcgtcgcaaccctgct 21232319


Query: 376699   gtgtggatcattgctagagaggaggacgcttgacctccttcaccttctcctaaggatctg 376758
                ||||||||||| ||||||||||||||||||||||||||||||||||||||||||||||||
Sbjct: 21232318 gtgtggatcatcgctagagaggaggacgcttgacctccttcaccttctcctaaggatctg 21232259


Query: 376759   caaggaaacagggatatacgatctccctaggtaacacaatatactctatacgcagttttg 376818
                ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Sbjct: 21232258 caaggaaacagggatatacgatctccctaggtaacacaatatactctatacgcagttttg 21232199

Thank you in advance

Answer 1

[Pierre Lindenbaum]

 seq 1 11 |while read L; do  awk -v C="$L" 'BEGIN{ok=0;s=sprintf(">chr%02d",int(C));} /^>chr/ {ok=$0==s;} { if(ok) print ;} ' input.blast > input_${L}.blast ; done