Shell Programming and Scripting

#!/bin/ksh

columns=""
heading_line=`head -1 file.txt`
selection="$*"                     # Read command line argments for the columns wanted.
separator="\t"

i=1
for heading in $heading_line
do
   for item in $selection
   do
      if [ "$heading" = "$item" ]
      then
         columns="$columns,"
      fi
   done
   ((i=$i+1))
done

columns="${columns%,}"             # Trim off trailing comma

cut -f $columns -d "$separator" file.txt

#!/bin/sh

file="$1"; shift

awk -v cols="$*" '
BEGIN{
	split(cols,C)
	OFS=FS="\t"
	getline
	split($0,H)
	for(c in C){
		for(h in H){
			if(C[c]==H[h])F[i++]=h
		}
	}
}
{ l="";for(f in F){l=l $F[f] OFS}print l }

' "$file"

#!/usr/bin/perl

  use strict;
  use warnings;

  use Getopt::Std;

  our $opt_c = '';

  getopt('c');

  die "Error: must specify a comma-separated list of columns with -c"
    unless $opt_c;

  my @wantedcols = split(/,/, $opt_c);

  my $collist = <>;
  die "Error: input file must have a first line with column names"
    unless $collist;
  chomp $collist;
  my @cols = split(' ', $collist);
  my @colindices;

  foreach my $col_index (0 .. $#cols) {
    push @colindices, $col_index if grep {/$cols[$col_index]/} @wantedcols;
  }

  while (my $line = <>) {
    chomp $line;
    my @colsin = split(' ', $line);
    print join ' ', @colsin[@colindices];
    print "\n";
  }

#!/bin/sh

file="$1"; shift

awk -v cols="$*" '
BEGIN{
	split(cols,C)
	OFS=FS="\t"
	getline
	split($0,H)
	for(c in C){
		for(h in H){
			if(C[c]==H[h])F[i++]=h
		}
		l=l C[c] OFS
	}
	print l
}
{ l="";for(f in F){l=l $F[f] OFS}print l }

' "$file"

#!/bin/sh

file="$1"; shift

awk -v c="$*" '
BEGIN{split(c,C);OFS=FS="\t"}
NR==1{
  for(c in C){
    f=0;while(f++<NF){
      if(C[c]==$f)F[i++]=f
}}}
{l="";for(f in F)l=l $F[f] OFS}
$0=l' "$file"

exit 0