AWK - passing generated string as code for awk from command line

Question

I am trying to dynamically print selected fields of a file using awk.

Basically, the question is why this one works:

awk -F';' '{print $3 ";" $4 ";" }' file

but this does not:

awk -F';' '{print '`echo '$3 ";" $4 ";"'`' }' file

My final goal is to encapsulate the above in one command so that I would be able to do

my_cmd ';' 3 6 7 8 file(s)

which should display the fields #3,6,7,8 delimited by ; from file(s).

Editing my post: Found out myself that my problem was echo was inserting of course a new line caracter which was causing issue for awk :o) \c did the trick, also some \" escaping had to do (see below).

awk -F';' '{print '"`echo '$3 \";\" $4 \";\"\c'`"' }' file(s)

Now I'm only left to change it with command which will generate dinamically a string like $2 ";' $5 ";' $6 ";' $9 ";" (number and fields should be the intput) etc. which should go between '{print ' and ' }'

Thanks to cbuckley I found out my one line command: (Issue solved).

cut -d"$1" -f `shift; echo $* | sed 's/[^ 0-9]\{1,\}.*$//;s/[ ]$//;s/[ ]\{1,\}/,/g'` `shift; printf "%s\n" $(echo $*) | grep -v '^[0-9]$'`

here $* are the input parameters and if above would be as an alias or a function in your .rc file named say filterc then the synopsys would be:

filterc delimiter column1 [column2 [column3...]] file1 [file2 [file3...]]  

where:

delimiter - one char only

column1..n - a number representing the column

file1..n - files to be filtered, assumption here that files will not have names from numbers only and that all are of same format.

Answer 1

Your command sounds very similar to cut:

cut -d ';' -f 1,3 <<EOT
one;two;three
foo;bar;quux
EOT

one;three
foo;quux

cut -d '-' -f 2,4 <<EOT
one-two-three-four
five-six-seven-eight
EOT

two-four
six-eight

Answer 2

Is this what you are after?

#!/bin/bash

get_columns()
{
    local fs=$1; shift
    local _awk=
    local column

    for column; do
        _awk="${_awk}\$${column},"
    done
    awk -F"$fs" -v OFS="$fs" "{ print ${_awk%,} }"
}

get_columns ';' 1 3 <<EOT
one;two;three
foo;bar;quux
EOT

get_columns '-' 2 4 <<EOT
one-two-three-four
five-six-seven-eight
EOT

-

$ ./t.sh
one;three
foo;quux
two-four
six-eight