CODEWITHSUNDEEP
bashshellawk
Rob
Rob

Reputation: 351

Bash retrieve column number from column name

Is there a better way (such as a one liner in AWK) where I can get the column number in a table with headings from a column name? I want to be able to process a column independent of what the column number actually is (such as when another column is added the script will not need to change).

For example, given the following table in "table.tsv":

ID  Value   Target  Not Used
1   5   9   11
2   4   8   12
3   6   7   10

I can do a sort on the "Target" column using:

#!/bin/bash
(IFS=$'\t'; read -r; printf "%s\n" "$REPLY"; i=0; for col in $REPLY; do
    ((++i))
    [ "$col" == "Target" ] && break
done; sort -t$'\t' "-k$i,${i}n") < table.tsv

Is there a way to do it without the for loop (or at least clean it up a little)?

The expected output of the given script is:

ID      Value   Target  Not Used
3       6       7       10
2       4       8       12
1       5       9       11

However, I was trying to give an example of what I was trying to do. I want to pass/filter my table through several programs so the headings and all columns should be preserved: just have processing occur at each step. In pseudo code, what I would like to do is:

print headings from stdin
i=$(magic to determine column position given "Target")
sort -t$'\t' "-k$i,${i}n"  # or whatever processing is required on that column

Upvotes: 7

Views: 13576

Answers (3)

karakfa
karakfa

Reputation: 67507

another alternative with a lot of pipes

$ head -1 table | tr -s ' ' '\n' | nl -nln |  grep "Target" | cut -f1

extract first row, transpose, number lines, find column name, extract number

Or, awk to the rescue!

$ awk -v RS='\t' '/Target/{print NR; exit}' file.tsv
3

Upvotes: 11

anubhava
anubhava

Reputation: 785581

Here is an awk alternative:

awk -F '\t' -v col='Target' 'NR==1{for (i=1; i<=NF; i++) if ($i == col){c=i; break}}
      {print $c}' file

EDIT: To print column number only:

awk -F '\t' -v col='Target' 'NR==1{for (i=1; i<=NF; i++) if ($i==col) {print i;exit}}' file
3

Upvotes: 6

Ed Morton
Ed Morton

Reputation: 204015

$ awk -v name='Target' '{for (i=1;i<=NF;i++) if ($i==name) print i; exit}' file
3

Upvotes: 3

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