Center a man page within a wide terminal

manc

#!/bin/bash
manc () 
{ 
    local DEFAULT_WIDTH=100
    local manpage margin pad
    local width=$DEFAULT_WIDTH
    local termwidth=$(tput cols)

    while (( $# )); do
        case $1 in
            -w*|--width*)
                if [[ $1 =~ --?w(idth=)?([1-9][0-9]*)$ ]];
                then
                    width=${BASH_REMATCH[2]}
                else
                    shift
                    if [[ -z ${1:-} || ! $1 =~ ^[1-9][0-9]*$ ]]; then
                        echo "ERROR: The -w / --width option expects an" \
                             "integer argument." >&2
                        return 1
                    fi
                    width=$1
                fi
                ;;
            -*)
                echo "ERROR: Unrecognized option '$1'." >&2
                return 1
                ;;
            *)
                if [[ ${manpage:-} ]]; then
                    echo "ERROR: One manual page at a time, please!" >&2
                    return 1
                fi
                manpage=$1
                ;;
        esac
        shift
    done

    if (( termwidth < width )); then
        echo "WARNING: '-w $width' is wider than the terminal." >&2
        width=$termwidth
    else
        margin=$(( (termwidth - width) / 2 ))
        pad=$(printf "%${margin}s")
    fi

    if [[ -z $manpage ]]; then
        echo "What manual page do you want?"
        return  # on macOS/BSD anyway, this *doesn't* return failure
    fi

    (
        (( ${DEBUG:-} )) && set -x
        set -eo pipefail

        manpath=$(man -w $manpage)
        groff -Tascii -rLL=${width}n -man $manpath \
          | sed "s/^/$pad/" \
          | ${PAGER:-less -FRX}
    )
}

if [[ -z ${PS1:-} ]]; then
    manc "$@"
fi

Installation

Assuming a reasonably default macOS or Linux box and the Bash shell:

GIST=https://gist.githubusercontent.com/ernstki/70c110249ff784c2144656f884bdd5b5/raw
mkdir -p ~/bin
curl "$GIST" > ~/bin/manc
chmod a+x ~/bin/manc

# make sure it works
manc

It's quite rare for it not to be these days, but if $HOME/bin is not in your search path, you can update that in your ~/.bash_profile or ~/.profile (whichever one you have):

export PATH=$HOME/bin:$PATH

Log (completely) out and back in in order for this change to take effect.