Bash script to center fortune/text from stdin/pipe

Here is my script center.sh:

#!/bin/bash

readarray message < <(expand)

width="${1:-$(tput cols)}"

margin=$(awk -v "width=$width" '
    { max_len = length > width ? width : length > max_len ? length : max_len }
    END { printf "%" int((width - max_len + 1) / 2) "s", "" }
' <<< "${message[@]}")

printf "%s" "${message[@]/#/$margin}"

How it works:

• the first command puts each line of stdin in array message after converting tabulations to spaces (thanks to @NominalAnimal)
• the second command reads the window width from parameter #1 and put it in variable width. If no parameter is given, the actual terminal width is used.
• the third command sends the whole message to awk in order to produce the left margin as a string of spaces which is put in variable margin.
  • the first awk line is executed for each input line. It calculates max_len, the length of the longest input line (capped to width)
  • the second awk line is executed when all input lines have been processed. It prints a string of (width - max_len) / 2 white space characters
• the last command prints every line of message after prepending margin to them

Test :

$ fortune | cowthink | center.sh
                    _______________________________________
                   ( English literature's performing flea. )
                   (                                       )
                   ( -- Sean O'Casey on P. G. Wodehouse    )
                    ---------------------------------------
                           o   ^__^
                            o  (oo)\_______
                               (__)\       )\/\
                                   ||----w |
                                   ||     ||

$ echo $'|\tTAB\t|' | center.sh 20
  |       TAB     |

$ echo "A line exceeding the maximum width" | center.sh 10
A line exceeding the maximum width

Finally, if you want to end the display with a separation line, like in your Python script, add this line before the last printf command:

message+=( $(IFS=''; sed s/./─/g <<< "${message[*]}" | sort | tail -n1)$'\n' )

What it does is replace every character in every line with a ─, select the longest with sort | tail -n1, and add it at the end of the message.

Test:

$ fortune | center.sh  60
     Tuesday is the Wednesday of the rest of your life.
     ──────────────────────────────────────────────────