center a file of text visually in the terminal (for ascii art)

center.awk

#!/usr/bin/awk -f

BEGIN {
	"tput cols" | getline c
	while(getline < ARGV[1])
	{
		if(length>l){l=length}
	}
	w=(c-l)/2
}
{
	printf "%*s%s\n",w,"",$0
}

center.sh

#!/bin/sh
# Centers a text document as a whole, preserving indentation of
# each line, across the width of the terminal.

# get width of longest line in text file
w=$(awk '{if(length>L){L=length}}END{print L}' < "$1")
# get terminal width
c=$(tput cols)
# output file to stdout, offset to center all content
awk -v l="$(((c - w)/2))" '{printf "%*s%s\n",l,"",$0}' "$1"

eridanus.txt

..
   .
    . . .
        .
 .......
   ..
     .
      .
      .
      .

usage:

$ ./center.sh eridanus.txt