Convert a fixed-width file to a delimiter-separated file such as CSV and TSV.

fixed-width-format-cut-paste.sh

#!/bin/bash

#
# Convert a fixed-width file to a delimiter-separated file such as CSV and TSV.
#
# Positional parameters:
#
#     FIELD_WIDTHS: a space-separated list the numbers of characters of each field in order of occurence.
#     SEPARATOR: the character used to separate the fields in the output. The default separator is a tabulation.
#     INPUT_FILE: the optional input file or `/dev/stdin` if no input file is provided.
#     OUTPUT_FILE: the optional output file or `/dev/stdout` if no output file is provided.
#
# Usage:
#
#     cat <<EOF | ./fixed-width-format-cut-paste.sh "5 5 5 5 5" "," "/dev/stdin" "/dev/output"
#     1111122222333334444455555
#     1234512345123451234512345
#     EOF
#     11111,22222,33333,44444,55555
#     12345,12345,12345,12345,12345
#
# Read: https://en.wikipedia.org/wiki/Flat-file_database#Fixed-width_formats
#

field_widths="${1}";
separator=`printf "${2-\t}"`;
input_file="${3:-/dev/stdin}";
output_file="${4:-/dev/stdout}";
tempdir=`mktemp --directory`;

field=1;
position=1;

cat /dev/stdin >  "${tempdir}/input-file";

for i in $field_widths; do
    cut -c ${position}-$(( $position + $i - 1 )) "${tempdir}/input-file" > "${tempdir}/field-${field}";
    position=$(( $position + $i ));
    field=$(( field + 1 ));
done;

paste -d "$separator" "${tempdir}/field-"* > "${output_file}";

rm -rf "${tempdir}";

fixed-width-format.awk

#!/usr/bin/awk -f

#
# Convert a fixed-width file to a delimiter-separated file such as CSV and TSV.
#
# Parameters:
#
#     FIELD_WIDTHS: a space-separated list the numbers of characters of each field in order of occurence.
#     SEPARATOR: the character used to separate the fields in the output. The default separator is a tabulation.
#
# Usage:
#
#     cat <<EOF | awk -v FIELD_WIDTHS="5 5 5 5 5" -v SEPARATOR="," -f fixed-width-format.awk 
#     1111122222333334444455555
#     1234512345123451234512345
#     EOF
#     11111,22222,33333,44444,55555
#     12345,12345,12345,12345,12345
# 
# It may be useful for implementations of AWK other than GNU's AWK, which supports splitting fixed-width files into fields.
#
# Read: https://en.wikipedia.org/wiki/Flat-file_database#Fixed-width_formats
#

BEGIN {
    SEP = SEPARATOR ? SEPARATOR : "\t";
    split(FIELD_WIDTHS, FIELD_WIDTHS_ARRAY);
    NUMBER_OF_FIELDS = length(FIELD_WIDTHS_ARRAY);
}

function split_into_fields() {
    position = 0;
    for (i = 1; i <= NUMBER_OF_FIELDS; i++) {
        position = position + FIELD_WIDTHS_ARRAY[i] + 1;
        if (position <= length($0)) {
            $0 = substr($0, 1, position - 1) SEP substr($0, position);
        }
    }
}

{
    split_into_fields();
    print $0;
}

fixed-width-format.sh

#!/bin/bash

#
# Convert a fixed-width file to a delimiter-separated file such as CSV and TSV.
#
# Positional parameters:
#
#     FIELD_WIDTHS: a space-separated list the numbers of characters of each field in order of occurence.
#     SEPARATOR: the character used to separate the fields in the output. The default separator is a tabulation.
#     INPUT_FILE: the optional file to be converted or `/dev/stdin` if no input file is provided.
#
# Usage:
#
#     cat <<EOF | ./fixed-width-format.sh "5 5 5 5 5" "," "/dev/stdin"
#     1111122222333334444455555
#     1234512345123451234512345
#     EOF
#     11111,22222,33333,44444,55555
#     12345,12345,12345,12345,12345
#
# Read: https://en.wikipedia.org/wiki/Flat-file_database#Fixed-width_formats
#

field_widths="${1}";
separator=`printf "${2-\t}"`;
input_file="${3:-/dev/stdin}";

split_into_fields() {
    local line="${1}"
    local position=0;
    for i in $field_widths; do
        position=$(( $position + $i + 1 ));
        if [ $position -le "${#line}" ]; then
            line="${line:0:$position-1}${separator}${line:$position-1}"
        fi;
    done;
    echo "${line}";
}

while read -r line; do
  split_into_fields "$line"
done < "${input_file}";