Question

I am trying to work out the proper process of installing with Wget, in this example I’ll use Nginx.

# Download nginx to /tmp/ directory
wget http://nginx.org/download/nginx-1.3.6.tar.gz -r -P /tmp

# Extract nginx into /tmp/nginx directory
tar xzf nginx-1.3.6.tar.gz -C /tmp/nginx

# Configure it to be installed in opt
./configure --prefix=/opt/nginx

# Make it
make

# Make install
make install

# Clean up temp folder
rm -r /tmp/*

Is this the idealised process? Is there anything I can improve on?

Answer 1

First of all, you definitely seem to reinvent the wheel: if the problem that you want to solve is automated packaging / building software on target systems, then there are myriads of solutions available, in form of various package management systems, port builders, etc.

As for your shell script, there are a couple of things you should consider fixing:

• Stuff like http://nginx.org/download/nginx-1.3.6.tar.gz or nginx-1.3.6.tar.gz are constants. Try to extract all constants in separate variables and use them to make maintaining this script a little bit easier, for example:

  NAME=nginx
  VERSION=1.3.6
  FILENAME=$NAME-$VERSION.tar.gz
  URL=http://nginx.org/download/$FILENAME
  TMP_DIR=/tmp
  INSTALL_PREFIX=/opt
  
  wget "$URL" -r -P "$TMP_DIR"
  tar xzf "$FILENAME" -C "$TMP_DIR/nginx"
  

• You generally can’t be 100% sure that wget exists on target deployment system. If you want to maximize portability, you can try to detect popular networking utilities, such as wget, curl, fetch or even lynx, links, w3m, etc.

• Proper practices on using a temporary directory is a long separate question, but, generally, you’ll need to adhere to 3 things:

  • One should somehow find out the temporary directory location. Generally, it’s wrong to assume that /tmp is always a temporary directory, as it can be not mounted, it can be non-writable, if can be tmpfs filesystem which is full, etc, etc. Unfortunately, there’s no portable and universal way to detect what temporary directory is. The very least one should do is to check out contents of $TMPDIR to make it possible for a user to point the script to proper temporary dir. Another possibly bright idea is a set of heuristic checks to make sure that it’s possible to write to desired location (checking at least $TMPDIR, $HOME/tmp, /tmp, /var/tmp), there’s decent amount of space available, etc.
  • One should create a temporary directory in a safe manner. On Linux systems, mktemp --tmpdir -d some-unique-identifier.XXXXXXXXX is usually enough. On BSD-based systems, much more manual work needed, as default mktemp implementation is not particularly race-resistant.

  • One should clean up temporary directory after use. Cleaning should be done not only on a successful exit, but also in a case of failure. This can be remedied with using a signal trap and a special cleanup callback, for example:

    # Cleanup: remove temporary files
    cleanup()
    {
            local rc=$?
            trap - EXIT
    
            # Generally, it's the best to remove only the files that we
            # know that we have created ourselves. Removal using recursive
            # rm is not really safe.
            rm -f "$LOCAL_TMP/some-file-we-had-created"
            [ -d "$LOCAL_TMP" ] && rmdir "$LOCAL_TMP"
    
            exit $rc
    }
    trap cleanup HUP PIPE INT QUIT TERM EXIT
    
    # Create a local temporary directory
    LOCAL_TMP=$(mktemp --tmpdir -d some-unique-identifier.XXXXXXXXX)
    
    # Use $LOCAL_TMP here
    

• If you really want to use recursive rm, then using any * to glob files is a bad practice. If your directory would have more than several thousands of files, * would expand to too much arguments and overflow shell’s command line buffer. I might even say that using any globbing without a good excuse is generally a bad practice. The rm line above should be rewritten at least as:

  rm -f /tmp/nginx-1.3.6.tar.gz
  rm -rf /tmp/nginx
  

  Removing all subdirectories in /tmp (as in /tmp/*) is a very bad practice on a multi-user system, as you’ll either get permission errors (you won’t be able to remove other users’ files) or you’ll potentially heavily disrupt other people’s work by removing actively used temporary files.

• Some minor polishing:

  • POSIX-standard tar uses normal short UNIX options nowadays, i.e. tar -xvz, not tar xvz.
  • Modern GNU tar (and, AFAIR, BSD tar too) doesn’t really need any of “uncompression” flags, such as -z, -j, -y, etc. It detects archive/compression format itself and tar -xf is sufficient to extract any of .tar / .tar.gz / .tar.bz2 tarballs.