feat(user/space4):Add script to space out stdin every 4 lines

diff --git a/user/space4 b/user/space4
new file mode 100755 (executable)
index 0000000..823f412
--- /dev/null
+++ b/user/space4
@@ -0,0 +1,52 @@
+#!/usr/bin/env bash
+# Desc: Adds blank line every 4 lines
+# Usage: cat file | space4
+# Example: seq 1 10 | space 4
+# Version: 0.0.1
+# Depends: Bash 5.1.16
+
+yell() { echo "$0: $*" >&2; } # print script path and all args to stderr
+die() { yell "$*"; exit 111; } # same as yell() but non-zero exit status
+must() { "$@" || die "cannot $*"; } # runs args as command, reports args if command fails
+read_stdin() {
+    # Desc: Consumes stdin; outputs as stdout lines
+    # Input: stdin (consumes)
+    # Output: stdout (newline delimited)
+    # Example: printf "foo\nbar\n" | read_stdin
+    # Depends: GNU bash (version 5.1.16)
+    # Version: 0.0.1
+    local input_stdin output;
+
+    # Store stdin
+    if [[ -p /dev/stdin ]]; then
+        input_stdin="$(cat -)";
+    fi; 
+    
+    # Store as output array elements
+    ## Read in stdin
+    if [[ -n $input_stdin ]]; then
+        while read -r line; do
+            output+=("$line");
+        done < <(printf "%s\n" "$input_stdin");
+    fi;
+
+    # Print to stdout
+    printf "%s\n" "${output[@]}";
+}; # read stdin to stdout lines
+main() {
+    # Depends: BK-2020-03: yell(), die(), must(), read_stdin()
+    if [[ $# -gt 0 ]]; then die "FATAL:This script uses no positional arguments.:$#"; fi;
+    n=0;
+    while read -r line; do
+        printf "%s\n" "$line";
+        if ! (( (n + 1) % 4 )); then
+            printf "\n";
+        fi;
+        ((n++));
+    done < <(read_stdin);
+}; # main program
+
+main "$@";
+
+# Author: Steven Baltakatei Sandoval
+# License: GPLv3+