halias

#!/bin/bash
#
# HOSTALIASES manager
#
# Author: Paul Armstrong

set -u

readonly ALIASES_DIR=~/.hostaliases.d
readonly ALIASES_LINK=~/.hostaliases

die() {
  echo $@ >&2
  exit 1
}

err() {
  echo $@ >&2
}

usage() {
  cat <<EOF
USAGE: halias add|create|current||list|remove|use args

ARGS:
* add: alias hostname
* create: file
* remove: alias
* show: file (optional)
* use: file

COMMANDS:
add: Add an alias to the current file
create: Creates a new file and switches to it
current: Show the currently active file
list: List the available files
remove: Remove an alias from the current file
show: Show the contents of the given file (or the current one if no args given)
use: Switch to the specified file

Files are kept in ${ALIASES_DIR}

To use the aliases, you need to put the following line in your 
.profile or .bash_profile (and run it for current terminals):
export HOSTALIASES=${ALIASES_LINK}

EOF
  exit 1
}

if [[ $# -lt 1 ]]; then
  usage
fi

if [[ ! $1 =~ add|create|current|list|remove|show|use ]]; then
  err "$1 is not a recognized argument"
  err ""
  usage
fi

if [[ ! -d "${ALIASES_DIR}" ]]; then
  mkdir  "${ALIASES_DIR}" || die "Unable to create ${ALIASES_DIR}"
fi

case $1 in
  'add')
    if [[ $# -ne 3 ]]; then
      die "add requires an aliase and a hostname"
    fi
    check=$(awk '{print $1}' "${ALIASES_LINK}" | grep -w $2)
    if [[ ! -z "${check}" ]]; then
      die "$2 already exists"
    fi
    echo "$2 $3" >> "${ALIASES_LINK}"
  ;;
  'current')
    if [[ ! -f "${ALIASES_LINK}" ]]; then
      die "${ALIASES_LINK} does not exist. HOSTALIASES is not configured."
    fi
    ls -al "${ALIASES_LINK}" | awk '{print $NF}' | awk -F/ '{print $NF}'
  ;;
  'create')
    if [[ $# -ne 2 ]]; then
      die "create requires a file name"
    fi
    aliases_file="${ALIASES_DIR}/$2"
    if [[ -f "${aliases_file}" ]]; then
      die "${aliases_file} already exists"
    fi
    touch "${aliases_file}"
    ln -sf "${aliases_file}" "${ALIASES_LINK}" \
      || die "Unable to link ${ALIASES_LINK} to ${aliases_dir}"
  ;;
  'list')
    ls "${ALIASES_DIR}"
  ;;
  'remove')
    if [[ $# -ne 2 ]]; then
      die "remove requires an aliase"
    fi
    tempfile=$(mktemp /tmp/${0}.XXXXXXXX)
    if [[ ! -f "${tempfile}" ]]; then
      die "Unable to create temp file"
    fi
    grep -vE "^${2}[[:space:]]" "${ALIASES_LINK}" > "${tempfile}"
    if [[ ! -s "${tempfile}" ]]; then
      err "You have removed the last entry. Continue Y|N?"
      while read line; do
        case "${line}" in
          Y|y)
            break
          ;;
          N|n)
            exit
          ;;
        esac
      done
    fi
    mv "${tempfile}" "${ALIASES_LINK}"
  ;;
  'show')
    if [[ $# -eq 2 ]]; then
      file="${ALIASES_DIR}/$2"
    else
      file="${ALIASES_LINK}"
    fi
    if [[ ! -f "${file}" ]]; then
      die "${file} does not exist"
    fi
    cat "${file}"
  ;;
  'use')
    if [[ $# -ne 2 ]]; then
      die "use requires a file"
    fi
    if [[ ! -f "${ALIASES_DIR}/$2" ]]; then
      die "$2 does not exist"
    fi
    ln -sf "${ALIASES_DIR}/$2" "${ALIASES_LINK}" \
      || die "Unable to link ${ALIASES_LINK} to ${aliases_dir}"
  ;;
esac