read in bash on whitespace-delimited file without empty fields collapsing

Question

I\'m trying to read a multi-line tab-separated file in bash. The format is such that empty fields are expected. Unfortunately, the shell is collapsing together field separat

Answer 1

Here's an approach with some niceties:

• input data from wherever becomes a pseudo-2D array in the main code (avoiding a common problem where the data is only available within one stage of a pipeline).
• no use of awk, tr, or other external progs
• a get/put accessor pair to hide the hairier syntax
• works on tab-delimited lines by using param matching instead of IFS=

The code. file_data and file_input are just for generating input as though from a external command called from the script. data and cols could be parameterized for the get and put calls, etc, but this script doesn't go that far.

#!/bin/bash

file_data=( $'\t\t'       $'\t\tbC'     $'\tcB\t'     $'\tdB\tdC'   \
            $'eA\t\t'     $'fA\t\tfC'   $'gA\tgB\t'   $'hA\thB\thC' )
file_input () { printf '%s\n' "${file_data[@]}" ; }  # simulated input file
delim=$'\t'

# the IFS=$'\n' has a side-effect of skipping blank lines; acceptable:
OIFS="$IFS" ; IFS=$'\n' ; oset="$-" ; set -f
lines=($(file_input))                    # read the "file"
set -"$oset" ; IFS="$OIFS" ; unset oset  # cleanup the environment mods.

# the read-in data has (rows * cols) fields, with cols as the stride:
data=()
cols=0
get () { local r=$1 c=$2 i ; (( i = cols * r + c )) ; echo "${data[$i]}" ; }
put () { local r=$1 c=$2 i ; (( i = cols * r + c )) ; data[$i]="$3" ; }

# convert the lines from input into the pseudo-2D data array:
i=0 ; row=0 ; col=0
for line in "${lines[@]}" ; do
    line="$line$delim"
    while [ -n "$line" ] ; do
        case "$line" in
            *${delim}*) data[$i]="${line%%${delim}*}" ; line="${line#*${delim}}" ;;
            *)          data[$i]="${line}"            ; line=                     ;;
        esac
        (( ++i ))
    done
    [ 0 = "$cols" ] && (( cols = i )) 
done
rows=${#lines[@]}

# output the data array as a matrix, using the get accessor
for    (( row=0 ; row < rows ; ++row )) ; do
   printf 'row %2d: ' $row
   for (( col=0 ; col < cols ; ++col )) ; do
       printf '%5s ' "$(get $row $col)"
   done
   printf '\n'
done

Output:

$ ./tabtest 
row  0:                   
row  1:                bC 
row  2:          cB       
row  3:          dB    dC 
row  4:    eA             
row  5:    fA          fC 
row  6:    gA    gB       
row  7:    hA    hB    hC