I have a file like this with tab delimiter:

Chr1    mak   gene    120221  120946  .       +       .       ID=spa-h0003.02;Name=spa-h0003.02
Chr1    mak   mRNA    120221  120946  .       +       .       ID=spa-cap_Chr1_00M;Parent=spa-h0003.02;Name=spa-cap_Chr1_00M
Chr1    mak   exon    120221  120946  .       +       .       Parent=spa-cap_Chr1_00M
Chr1    mak   gene    18546165        18546939        .       +       .       ID=spa-h0004.02;Name=spa-h0004.02
Chr1    mak   mRNA    18546165        18546939        .       +       .       ID=spa-cap_Chr1_18;Parent=spa-h0004.02;Name=spa-cap_Chr1_18
Chr1    mak   exon    18546165        18546504        .       +       .       Parent=spa-cap_Chr1_18
Chr1    mak   exon    18546791        18546939        .       +       .       Parent=spa-cap_Chr1_18

I want to replace different strings only if the third column has "gene". But strings on the ninth column should be replaced according to information present in a second file like this one (with tabs):

spa-h0003.02  spa-cap_Chr1_00M
spa-h0004.02  spa-cap_Chr1_18

I am not sure how to do it. I was thinking something like (XX should be the info from the second file?):

cat file | awk '$3 == "gene" && $9 == "spa-" {$9 = "XX"} {print}' 

But how I can use the information from the second file? Maybe:

while read n k; do sed -i 's/$n/$k/g' file1; done < fileA
  • With the awk answers, you'll see NR == FNR which is a very common awk idiom meaning "when the line number of all lines seen equals the line number of this file" which can only be true for the first file given. – glenn jackman Oct 18 '18 at 15:57

Assuming file1 contains the text to be replaced, file2 contains the replacement text, and you can rely on the ID= to perform the lookup between both, you can use this (more popular i guess) awk script:

awk -F'\t' '
    a[$1]=$2                                   # fills the array a with the replacement text
  $3=="gene"{                                  # check only lines with 'gene'
    id=gensub("ID=([^;]*);.*","\\1",1,$9);     # extract the id string
    if(id in a)                                # if the id is part of the array a
       gsub(id,a[id])                          # replace it
  1                                            # print the line
' file2 file1
  • thanks, Oliv. Great explanation, I can understand step by step and learn from that. – Alex Oct 18 '18 at 16:09
  • @oliv: shouldn't you limit the gsub to $9? – RudiC Oct 18 '18 at 22:02
  • @RudiC You could but this has no influence on the given example. – oliv Oct 19 '18 at 6:16

An unpopular choice: Tcl. Tcl has a nice string map command that accomplishes exactly this. Unfortunately, Tcl is not really built for perl-ish one-liners.

echo '
    # read the mapping file into a list
    set fh [open "mapping" r]
    set content [read $fh]
    close $fh
    set mapping [regexp -all -inline {\S+} $content]

    # read the contents of the data file
    # and apply mapping to field 9 when field 3 is "gene"
    set fh [open "file" r]
    while {[gets $fh line] != -1} {
        set fields [split $line \t]
        if {[lindex $fields 2] eq "gene"} {
            lset fields 8 [string map $mapping [lindex $fields 8]]
        puts [join $fields \t]
    close $fh
' | tclsh

With awk, I'd write:

awk -F'\t' -v OFS='\t' '
    NR == FNR {repl[$1]= $2; next}
    $3 == "gene" {
        for (seek in repl) 
            while ((idx = index($9, seek)) > 0) 
                $9 = substr($9, 1, idx-1) repl[seek] substr($9, idx + length(seek))
' mapping file

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