simple shell client for tldr pages

tldr.sh

#!/bin/bash
# shellcheck disable=SC2002

# 1) Put this file into your local clone of git://github.com/tldr-pages/tldr:
#    curl -L https://gist.github.com/waldyrious/805d6357fa0b55135354ea4b996e0818/raw/ -o path/to/tldr-repo/tldr.sh
# 2) Mark it as executable:
#    chmod +x path/to/tldr-repo/tldr.sh
# 3) symlink it into /usr/local/bin:
#    sudo ln -s /absolute/path/to/tldr-repo/tldr.sh /usr/local/bin/tldr

command_args="$*"

if [[ -z "${command_args// }" ]];
then
    $0 tldr # If no parameters are passed, default to the "tldr.md" page
    # HTTP redirection status code 303 = See Other.
    # This will actually exit with error code 47, because exit codes are modulo 256.
    exit 303;
fi

# Merge multiple arguments into a single hyphenated argument
command=${command_args// /-}
len=${#command}
heading=$(printf '=%.0s' $(seq 1 "$len"))

# Convert the local platorm name to tldr's version.
# (Copied from https://github.com/raylee/tldr)
get_platform() {
    case $(uname -s) in
        Darwin) echo "osx"    ;;
        Linux)  echo "linux"  ;;
        SunOS)  echo "sunos"  ;;
        *)      echo "common" ;;
    esac
}

platform=$(get_platform)

# Define a way to get this script's absolute path,
# since realpath() is not universally available (e.g. on macOS)
# source: http://stackoverflow.com/a/30795461/266309
script_abspath=$(perl -e 'use Cwd "abs_path"; print abs_path(@ARGV[0])' -- "$0")

# Change to the git repository's root
cd "$(dirname "$script_abspath")" || {
    echo "Error: couldn't enter the tldr directory.";
    # HTTP client error status code 502 = Bad Gateway
    # (This script received an invalid response from an upstream resource it needed to fulfill the request.)
    # This will actually exit with error code 246, because exit codes are modulo 256.
    exit 502;
}

if [[ "${command_args}" == "--update" ]]
then
    echo "Updating local tldr-pages repository..."
    git pull --rebase >/dev/null 2>&1
    exit 0;
else
    # If the local clone is more than a day old, update before proceeding.
    find .git/FETCH_HEAD -mtime -7 2>/dev/null | grep FETCH_HEAD >/dev/null || {
        echo -e "Local tldr-pages repository last updated over a week ago; auto-updating...\n";
        git pull --rebase >/dev/null 2>&1;
    }
fi

cd pages || {
    echo "Error: couldn't enter the pages directory";
    # See comment above about error code 502.
    exit 502;
}

# Look for a page in the platform-specific folder
if [ -f "$platform/$command.md" ]
then
    echo; # newline
    cat "$platform/$command.md" | \
    sed -E -e "s/^# (.+)/\1º${heading}/" | tr 'º' '\n' | \
    sed -E -e "s/^- (.+)/\1/" | \
    sed -E -e "s/^\`(.+)\`/    \1/"
    #pandoc -s -f markdown -t plain "$platform/$command.md"
# Look for a page in the common folder
elif [ -f "common/$command.md" ]
then
    echo; # newline
    cat "common/$command.md"    | \
    sed -E -e "s/^# (.+)/\1º${heading}/" | tr 'º' '\n' | \
    sed -E -e "s/^- (.+)/\1/" | \
    sed -E -e "s/^\`(.+)\`/    \1/"
    #pandoc -s -f markdown -t plain "common/$command.md"
else # No page was found, so list pages whose names start
    echo "No page was found for the '$*' command. Did you spell it right?"
    candidates=$(find common "$platform" -name "$command*" | sed -e "s|.*/||" -e "s|.md||")
    if [[ $candidates ]]
    then
        echo -n "Maybe you meant one of these: "
        echo "$candidates" | xargs | sed 's/ /, /g'
    fi
    echo -e "\nOtherwise, you could contribute the '$command.md' page! See \033[36mhttps://tldr-pages.github.io#contributing\033[0m."
    # HTTP client error status code 404 = Not Found.
    # This will actually exit with error code 148, because exit codes are modulo 256.
    exit 404
fi

TODO: implement a basic search command using something like grep -rl clipboard ~/repos/tldr/pages/

TODO: perhaps calls to external commands (uname, perl...) could be replaced with pure-bash alternatives -- see https://github.com/dylanaraps/pure-bash-bible#get-the-name-of-the-operating-system--kernel for an alternative to uname; not sure if realpath is replacable in (concise) pure bash code.