template-bash-command/command

#!/usr/bin/bash
# shellcheck disable=SC2016
set -e
# export PATH="/usr/bin:/usr/local/bin" # safer, if you can

(( BASH_VERSINFO[0] < 4 )) && echo "Bash 4+ required." && exit 1

: "${PAGER:=more}"
: "${EDITOR:=vi}"
: "${HELP_BROWSER:=}"

EXE="${0##*/}"

declare -A help # associative arrays *require* declaration

help[main]='
# Bash Template Command

*This `README.md` is autogenerated.*

This is a GitHub template repo that will be copied instead of forked to
create a new Bash command with a command something like this:

```
gh repo create rwxrob/mycmd -p rwxrob/template-bash-command
```

This `command` inside can then be renamed and finished.

Obviously, not all of this is needed for many Bash scripts, but anything
with more than two subcommands will benefit from the builtin tab
completion, embedded Markdown help documentation support, and included
functions (`usage`, `_filter`, `_buffer`, `_have`, etc.)

## Naming Conventions

* Name repos containing single bash commands with `cmd-`
* Name template repos beginning with `template-`
* Start command functions with `command_` to be completed
* Start command functions with `command__` to not be completed

## Dependencies

Required:

* Bash 4+

Optional:

* `pandoc` - for rich help docs

## Justification

Bash is the dominate shell scripting language and the official default
Linux interactive shell, which reduces cognitive overhead; every command
line *is* a line of code that could be put into script as is. Bash
scripts are at the core of cloud, containers, and Kubernetes. Bash 4+
with its associative array support, powerful regular expressions, and
multiple ways of feeding data to loops easily covers the needs
previously requiring Python and Perl scripts. Bash scripts are also much
more powerful, safer, flexible, and performant than POSIX shell or Zsh.

## Caveats

* Use the official bash path: `#!/usr/bin/bash`
* Using `#!/usr/bin/env bash` introduces unnecessary risk
* Always set the acceptable `PATH` at beginning of script
* Always check script with [`shellcheck`] before releasing
* Always use `bc` for *any* floating point math

[`shellcheck`]: <https://www.shellcheck.net>

## Legal

Copyright 2021 Rob Muhlestein <rob@rwx.gg>  
Released under Apache-2.0 License  
Please mention <https://youtube.com/rwxrob>  

'

help[foo]='Foos.'

command_foo() {
  _filter "$@" && return $?
  echo "would foo: $*"
}

help[bar]='Bars.'

command_bar() {
  _buffer "$@" && return $?
  echo "would bar: $*"
}

command__hidden() {
  _filter "$@" && return $?
  echo "would run _hidden: $*"
}

# ------------------ builtin commands and functions ------------------
#          (https://github.com/rwxrob/template-bash-command)

help[usage]='Displays a summary of usage.'

command_usage() {
  local -a cmds
  for c in "${COMMANDS[@]}"; do
    [[ ${c:0:1} =~ _ ]] && continue
    cmds+=($c)
  done
  cmds="${cmds[*]}"
  printf "usage: %s (%s)\n" "$EXE" "${cmds// /|}"
}

help[help]='
# Display Help Information

```
help [<command>]
```

Displays specific help information. If no argument is passed displays
general help information (main). Otherwise, the documentation for the
specific argument keyword is displayed, which usually corresponds to
a command name (but not necessarily). All documentation is written in
GitHub Flavored Markdown and will displayed as a web page if `pandoc`
and `$HELP_BROWSER` are detected, otherwise, just the Markdown is sent
to `$PAGER` (default: more).

Also see `readme` and `usage` commands.
'

command_help() { 
  local name="${1:-main}" title own body
  title=$(_help_title "$name")
  if [[ -z "$title" ]]; then
    body="${help[$name]}"
    title="$EXE $name"
    [[ $name = main ]] && title="$EXE"
  else
    body="${help[$name]}"
    local eol=$'\n'
    body=${body#*$title}
  fi
  local file="/tmp/help-$EXE-$name.html"
  if _have pandoc ; then
    if _have "$HELP_BROWSER" && [[ -t 1 ]] ;then
      pandoc -s --metadata title="$title" \
        -o "$file" <<< "$body"
      [[ -z "$2" ]] && cd /tmp && exec "$HELP_BROWSER" "$file"
      return 0
    fi
    pandoc -s --metadata title="$title" \
      -t plain <<< "$body" | "$PAGER"
    return 0
  fi
  echo -e "$title\n\n$body" | "$PAGER"
}

help[readme]='
# Generate `README.md` File

```
command readme > README.md
```

The `readme` command will output the embedded help documentation in raw
GitHub Flavored Markdown suitable for use as a `README.md` file on
GitHub or similar hosting service.  '

command_readme() {
  _trim "${help[main]}"
  local usage="$(command_usage)"
  printf "\n## Commands\n\n"
  local -a names=("${!help[@]}")
  while IFS= read -r name; do
    [[ $name = main ]] && continue
    local body=$(_trim "${help[$name]}")
    [[ $body =~ ^\# ]] || body="# The \`$name\` Command\n\n$body"
    printf "##$body\n\n"
  done < <(printf "%s\n" "${!help[@]}" | LC_COLLATE=C sort)
  echo -e "----\n\n*Autogenerated $(date)*\n"
}


_help_title() {
  _filter "$@" && return $?;
  local name="$1"
  while IFS= read -r line; do
    [[ $line =~ ^[:space]*$ ]] && continue
    [[ $line =~ ^#\ (.+) ]] && echo "${BASH_REMATCH[1]}" && return 0
    return 1
  done <<< "${help[$name]}"
}

_trim() {
  local it="${1#"${1%%[![:space:]]*}"}"
  echo -e "${it%"${it##*[![:space:]]}"}"
}

_have(){ type "$1" &>/dev/null; }

_filter(){
  [[ -n "$1" ]] && return 1
  while IFS= read -ra args; do
    "${FUNCNAME[1]}" "${args[@]}"
  done
}

_buffer() {
  [[ -n "$1" ]] && return 1
  "${FUNCNAME[1]}" "$(</dev/stdin)"
}

# --------------------- completion and delegation --------------------
#         (better than . <(foo bloated_completion) in .bashrc)

while IFS= read -r line; do
  [[ $line =~ ^declare\ -f\ command_ ]] || continue
  COMMANDS+=( "${line##declare -f command_}" )
done < <(declare -F)
COMMANDS=($(LC_COLLATE=C sort < <(printf "%s\n" "${COMMANDS[@]}")))

if [[ -n $COMP_LINE ]]; then
  line=${COMP_LINE#* }
  for c in "${COMMANDS[@]}"; do
    [[ ${c:0:${#line}} == "${line,,}" && ${c:0:1} != _ ]] && echo "$c"
  done
  exit
fi

for c in "${COMMANDS[@]}"; do
  if [[ $c == "$EXE" ]]; then
    "command_$EXE" "$@"
    exit $?
  fi
done

if [[ -n "$1" ]]; then
  declare cmd="$1"; shift
  for c in "${COMMANDS[@]}"; do
    if [[ $c == "$cmd" ]]; then
      "command_$cmd" "$@"
      exit $?
    fi
  done
fi

command_usage "$@"