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Add `chr` to first column of specific rows?

I have a .gtf file as below I would like to add "chr" to the first column of the file but not in first 5 rows?

#!genome-build GRCh37.p13
#!genome-version GRCh37
#!genome-date 2009-02
#!genome-build-accession NCBI:GCA_000001405.14
#!genebuild-last-updated 2013-09
1       ensembl chromosome      1       300239041       .       .       .       ID=1;Name=chromosome:AGPv1:1:1:300239041:1
1       ensembl exon    3       104     .       +       .       Parent=GRMZM2G060082_T01;Name=GRMZM2G060082_E07

output:

#!genome-build GRCh37.p13
#!genome-version GRCh37
#!genome-date 2009-02
#!genome-build-accession NCBI:GCA_000001405.14
#!genebuild-last-updated 2013-09
chr1       ensembl chromosome      1       300239041       .       .       .       ID=1;Name=chromosome:AGPv1:1:1:300239041:1
chr1       ensembl exon    3       104     .       +       .       Parent=GRMZM2G060082_T01;Name=GRMZM2G060082_E07

I used the foloww cods but it add "chr" to the first 5 lines, as well.

cat Homo_sapiens.GRCh37.gtf | sed 's/^/chr/' > chr.gtf
rna-seq r alignment
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updated by Chirag Parsania Chirag Parsania • written by star star

Check if a line starts with a number (and X/Y/MT) and only then add chr using sed.

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written by GenoMax GenoMax

Could be done using R, but this is more suitable to command line, sed, awk,...

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written by zx8754 zx8754

3 answers 

awk 'OFS="\t" {if (NR > 5) $1="chr"$1; print}' in.gtf

Could have been found on google easily...

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written by ATpoint ATpoint

I would have gone with:

cat <(grep '^#' file.txt) <(grep -v '^#' file.txt  | sed 's/^/chr/g')

In order to be more dynamical.

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written by Kairos Kairos

~ R way.

dd <- tibble::tribble(
  ~V1,       ~V2,          ~V3, ~V4,       ~V5, ~V6, ~V7, ~V8,                                               ~V9,
    1, "ensembl", "chromosome",   1, 300239041, ".", ".", ".",      "ID=1;Name=chromosome:AGPv1:1:1:300239041:1",
    1, "ensembl",       "exon",   3,       104, ".", "+", ".", "Parent=GRMZM2G060082_T01;Name=GRMZM2G060082_E07"
  )

dd2 <- dd %>% dplyr::mutate(V1 = paste("Chr" , V1 , sep=""))

# A tibble: 2 x 9
  V1    V2      V3            V4        V5 V6    V7    V8    V9                                             
  <chr> <chr>   <chr>      <dbl>     <dbl> <chr> <chr> <chr> <chr>                                          
1 Chr1  ensembl chromosome     1 300239041 .     .     .     ID=1;Name=chromosome:AGPv1:1:1:300239041:1     
2 Chr1  ensembl exon           3       104 .     +     .     Parent=GRMZM2G060082_T01;Name=GRMZM2G060082_E07
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written by Chirag Parsania Chirag Parsania

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