awk: sort file based on user input

Question

I have this simple awk code:

awk -F, 'BEGIN{OFS=FS} {print $2,$1,$3}' $1

Works great, except I've hardcoded how I want to sort the comma-delimited fields of my plaintext file. I want to be able to specify at run time in which order I'd like to sort my fields.

One hacky way I thought about doing this was this:

read first
read second
read third

TOTAL=$first","$second","$third

awk -F, 'BEGIN{OFS=FS} {print $TOTAL}' $1

But this doesn't actually work:

awk: illegal field $(), name "TOTAL"

Also, I know a bit about awk's ability to accept user input:

BEGIN {
    getline first < "-"
}

$1 == first {
}

But I wonder whether the variables created can in turn be used as variables in the original print command? Is there a better way?

chepner · Accepted Answer · 2016-03-31 18:23:20Z

3

You have to let bash expand $TOTAL before awk is called, so that awk sees the value of $TOTAL, not the literal string $TOTAL. This means using double, not single, quotes.

read first
read second
read third

# Dynamically construct the awk script to run
TOTAL="\$$first,\$$second,\$$third"
SCRIPT="BEGIN{OFS=FS} {print $TOTAL}"

awk -F, "$SCRIPT" "$1"

A safer method is to pass the field numbers as awk variables.

awk -F, -v c1="$first" -v c2="$second" -v c3="$third" 'BEGIN{OFS=FS} {print $c1, $c2, $c3}' "$1"

edited Mar 31, 2016 at 18:23

answered Mar 31, 2016 at 17:53

chepner

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2 Comments

chepner Over a year ago

I forgot to use -v for the other two variables.

dispepsi Over a year ago

Thanks, this is great!

Ed Morton · Accepted Answer · 2016-03-31 23:52:41Z

0

All you need is:

awk -v order='3 1 2' 'BEGIN{split(order,o)} {for (i=1;i<=NF;i++) printf "%s%s", $(o[i]), (i<NF?OFS:ORS)}'

e.g.:

$ echo 'a b c' | awk -v order='3 1 2' 'BEGIN{split(order,o)} {for (i=1;i<=NF;i++) printf "%s%s", $(o[i]), (i<NF?OFS:ORS)}'
c a b

$ echo 'a b c' | awk -v order='2 3 1' 'BEGIN{split(order,o)} {for (i=1;i<=NF;i++) printf "%s%s", $(o[i]), (i<NF?OFS:ORS)}'
b c a

answered Mar 31, 2016 at 23:52

Ed Morton

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