download-opam.sh

#!/bin/bash

set -e

echo "Downloading OPAM repository..."
curl -sL https://github.com/ocaml/opam-repository/archive/master.tar.gz | tar -xz
echo "Downloading packages..."
( cd opam-repository-master/packages/;
  for pkg in *; do ( cd $pkg; ls -v | head -n -1 | xargs rm -rf; ) done; )
( cd opam-repository-master/; opam admin cache -n ../_src --link ..; )
rm -rf opam-repository-master
echo "Unpacking sources..."

for archive in $(find . -maxdepth 2 -type l); do
    case $archive in
        *.tar.bz2|*.tbz) cmd='tar --force-local -xjf';;
        *.tar.xz) cmd='tar --force-local -xJf';;
        *.zip) cmd='unzip -q -n';;
        *.tar.gz|*.tgz|*.tar.gz) cmd='tar --force-local -xzf';;
        *) echo "Unknown archive type $archive, guessing tgz"; cmd='tar --force-local -xzf';;
    esac
    ( cd ${archive%/*}; $cmd ${archive##*/}; ) && rm $archive
    echo $archive
done

a shorter version in opam2 is : opam list -a -s | xargs -I'{}' opam source {}