Use `[:blank:]` or space as default split/join character

dotfiles/bash/main.bashrc

 
 nlfor() {
     #
-    # Replace $1 with newlines and fix final newline
+    # Replace $1 (or blank space) with newlines and fix final newline
     #
     # Shorthand for commonly used tr syntax.  Example:
     #
     # newline at the end of the replaced string.
     #
     local char=$1
+    test -n "$char" || char='[:blank:]'
     tr "$char" '\n' \
       | fixnl
 }
 
 nljoin() {
     #
-    # Join lines with $1
+    # Join lines with $1 (or space)
     #
     # Shorthand for commonly used tr syntax.  Example:
     #
     # newline/colon at the end of final string.
     #
     local char=$1
+    test -n "$char" || char=' '
     tr '\n' "$char" \
       | sed "s/$char*$//" \
       | fixnl -c