I need to transform some data into assignments. I'm pretty sure it looks like a pretty straightforward job for awk, but I am far from confortable with it.

Each data element (and columns) are tab-separated. Data elements may contain spaces and special characters, but no TABs.

example input :

column1 column2 column3
rowA1   rowA2   rowA3
rowB1   rowB2   rowB3

expected output :

column1 = rowA1
column2 = rowA2
column3 = rowA3

column1 = rowB1
column2 = rowB2
column3 = rowB3

(with arbitrary number of rows, not exceeding hundreds)

Any clue how to do this ? (with awk or any standard command-line tool on a linux)


For example:

    if (NR==1){
        for (i=1; i<=NF; ++i){
            arr[i] = $i
        for (i=1; i<=NF; ++i){
            print(arr[i]," = ",$i)

To run:

awk -f script.awk input
| improve this answer | |
  • I needed to insert this first line into your script: BEGIN { FS = "[\t]+" } ; , otherwise the fields containing spaces were shifted to wrong columns. It works nicely now. Thank you for helping me with my first awk task! – Pac0 Jul 25 '17 at 8:44
  • @Pac0 Right, I forgot you mentioned your file is separated by tabs. – pfnuesel Jul 25 '17 at 9:02
  • good script. i'd upvote if you took the time to explain how it works and turn it into a detailed answer. teaching is better than cargo-culting. Pac0 seems to understand it but anyone else who stumbles across this may not. Also, you seem to have a habit of writing awk script fragments and then saying "run with awk -f script.awk input" - that works, but why not just make it a #!/usr/bin/awk script? – cas Jul 25 '17 at 11:42
cat data |
while IFS=$'\t' read -r -a a; do
   case ${flag+'set'} in
      "set" )
         set -- "${a[@]}"
         for c in "${C[@]}"; do echo "$c = $1"; shift; done
         echo ;;

      * ) C=( "${a[@]}" ); flag= ;;

sed -Ee '
   s/^(\S+)\s*((\S.*)?)\n(\S+)\s*((\S.*)?)/\1 = \4\n\2\n\5/
' data

perl -F'\t+' -lane '
   @C or @C = @F,next;
   print "$C[$_] = $F[$_]" for 0 .. $#C;
   eof or print q[];
' data


column1 = rowA1
column2 = rowA2
column3 = rowA3

column1 = rowB1
column2 = rowB2
column3 = rowB3


  1. bash

    *) Store the first line in an array C during the time the flag is unset. Then promptly set it so that next time onwards we don't arrive here. *) The array a is split up into arguments using the set command. *) Then we cycle through the columns, accessed via, "${c[@]}" in a for loop and printed alongwith $1 ( which is then shifted out) *) Note IFS is set to tab via the $'\t' construct. Since it is one of special characters hence a run of these would be collapsed into one and so we won't be seeing empty fields.

  2. perl

    *) Set the FS to one or more TABs: -F'\t+' and turn on autosplit mode. *) Same logic as with bash based solution, wherein we store the columns data found in 1st line in the @C array. The arrays @C and current record fields data in @F are printed taking one from each.

  3. sed

    *) Here we first convert all TABs to spaces. *) Store the first line columns data in the hold space. *) For all the other lines, append the columns to the current row. *) Then we keep picking first elements from current row/column and shrinking the pattern space by taking away these printed stuff. *) Stop condition happens when no spaces are left.

| improve this answer | |
  • I prefer pfnuesel's simple awk answer, but I appreciate the try anyway. and +1 for detailed explanations. (Well, i would have given +1 but I haven't enough reputation to upvote yet, sorry!) – Pac0 Jul 25 '17 at 12:56

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