user/space4

   1 #!/usr/bin/env bash
   2 # Desc: Adds blank line every 4 lines
   3 # Usage: cat file | space4
   4 # Example: seq 1 10 | space 4
   5 # Version: 0.0.1
   6 # Depends: Bash 5.1.16
   7
   8 yell() { echo "$0: $*" >&2; } # print script path and all args to stderr
   9 die() { yell "$*"; exit 111; } # same as yell() but non-zero exit status
  10 must() { "$@" || die "cannot $*"; } # runs args as command, reports args if command fails
  11 read_stdin() {
  12     # Desc: Consumes stdin; outputs as stdout lines
  13     # Input: stdin (consumes)
  14     # Output: stdout (newline delimited)
  15     # Example: printf "foo\nbar\n" | read_stdin
  16     # Depends: GNU bash (version 5.1.16)
  17     # Version: 0.0.1
  18     local input_stdin output;
  19
  20     # Store stdin
  21     if [[ -p /dev/stdin ]]; then
  22         input_stdin="$(cat -)";
  23     fi;
  24
  25     # Store as output array elements
  26     ## Read in stdin
  27     if [[ -n $input_stdin ]]; then
  28         while read -r line; do
  29             output+=("$line");
  30         done < <(printf "%s\n" "$input_stdin");
  31     fi;
  32
  33     # Print to stdout
  34     printf "%s\n" "${output[@]}";
  35 }; # read stdin to stdout lines
  36 main() {
  37     # Depends: BK-2020-03: yell(), die(), must(), read_stdin()
  38     if [[ $# -gt 0 ]]; then die "FATAL:This script uses no positional arguments.:$#"; fi;
  39     n=0;
  40     while read -r line; do
  41         printf "%s\n" "$line";
  42         if ! (( (n + 1) % 4 )); then
  43             printf "\n";
  44         fi;
  45         ((n++));
  46     done < <(read_stdin);
  47 }; # main program
  48
  49 main "$@";
  50
  51 # Author: Steven Baltakatei Sandoval
  52 # License: GPLv3+