title: Explanation of the "--update add" command for Alpine Linux
body: <p>I'm trying to understand the Dockerfile <a href="https://hub.docker.com/r/rdsubhas/tor-privoxy-alpine/~/dockerfile/" rel="noreferrer">https://hub.docker.com/r/rdsubhas/tor-privoxy-alpine/~/dockerfile/</a>, which contains a <code>RUN</code> executive with</p>
  
  <pre><code>apk --update add privoxy tor@testing runit@testing
  </code></pre>
  
  <p>I wanted to check my understanding of how the <code>apk</code> command is being used, so I tried opening a terminal in the Alpine environment as follows:</p>
  
  <pre><code>docker run -it --rm alpine:latest /bin/ash
  </code></pre>
  
  <p>after which I simply ran <code>apk</code> to see its usage:</p>
  
  <pre><code>/ # apk
  apk-tools 2.6.8, compiled for x86_64.
  
  usage: apk COMMAND [-h|--help] [-p|--root DIR] [-X|--repository REPO]
             [-q|--quiet] [-v|--verbose] [-i|--interactive] [-V|--version]
             [-f|--force] [-U|--update-cache] [--progress] [--progress-fd FD]
             [--no-progress] [--purge] [--allow-untrusted] [--wait TIME]
             [--keys-dir KEYSDIR] [--repositories-file REPOFILE] [--no-network]
             [--no-cache] [--arch ARCH] [--print-arch] [ARGS]...
  
  The following commands are available:
    add       Add PACKAGEs to 'world' and install (or upgrade) them, while
              ensuring that all dependencies are met
    del       Remove PACKAGEs from 'world' and uninstall them
    fix       Repair package or upgrade it without modifying main dependencies
    update    Update repository indexes from all remote repositories
    info      Give detailed information about PACKAGEs or repositores
    search    Search package by PATTERNs or by indexed dependencies
    upgrade   Upgrade currently installed packages to match repositories
    cache     Download missing PACKAGEs to cache and/or delete unneeded files
              from cache
    version   Compare package versions (in installed database vs. available) or
              do tests on literal version strings
    index     Create repository index file from FILEs
    fetch     Download PACKAGEs from global repositories to a local directory
    audit     Audit the directories for changes
    verify    Verify package integrity and signature
    dot       Generate graphviz graphs
    policy    Show repository policy for packages
    stats     Show statistics about repositories and installations
  
  Global options:
    -h, --help              Show generic help or applet specific help
    -p, --root DIR          Install packages to DIR
    -X, --repository REPO   Use packages from REPO
    -q, --quiet             Print less information
    -v, --verbose           Print more information (can be doubled)
    -i, --interactive       Ask confirmation for certain operations
    -V, --version           Print program version and exit
    -f, --force             Do what was asked even if it looks dangerous
    -U, --update-cache      Update the repository cache
    --progress              Show a progress bar
    --progress-fd FD        Write progress to fd
    --no-progress           Disable progress bar even for TTYs
    --purge                 Delete also modified configuration files (pkg
                            removal) and uninstalled packages from cache (cache
                            clean)
    --allow-untrusted       Install packages with untrusted signature or no
                            signature
    --wait TIME             Wait for TIME seconds to get an exclusive repository
                            lock before failing
    --keys-dir KEYSDIR      Override directory of trusted keys
    --repositories-file REPOFILE Override repositories file
    --no-network            Do not use network (cache is still used)
    --no-cache              Read uncached index from network
    --arch ARCH             Use architecture with --root
    --print-arch            Print default arch and exit
  
  This apk has coffee making abilities.
  </code></pre>
  
  <p>The thing is, I don't see the <code>--update</code> option in this documentation (only <code>--update-cache</code>). </p>
  
  <p>What I suspect is that <code>apk --update add [package]</code> is simply shorthand for <code>apk update</code> followed by <code>apk add [package]</code>. Can anyone confirm this?</p>