What errors are you getting?

I wonder if this issue is related. Maybe try:

composer global update fxp/composer-asset-plugin --no-plugins

Actually I had tried and hit issues with Composer installation of v2.1.1.

@İşöğüçı They seem to have fixed it in fxp/composer-asset-plugin only in last 24 days, so you might try to give it another shot. Obviously don't use v1.1.1 anymore.

Thanks all. I can't install elgg from git. My instructions are:

git clone https://github.com/Elgg/Elgg

After I go into http://learn.elgg.org/en/2.0/intro/install.html

and execute the istructions:

composer self-update

[InvalidArgumentException]             
 Command "self-update" is not defined.

composer global require "fxp/composer-asset-plugin:~1.1.1"

Changed current directory to /home/daniele/.composer
PHP Fatal error:  Call to undefined method Composer\Package\Loader\ArrayLoader::parseLinks() in /home/daniele/.composer/vendor/fxp/composer-asset-plugin/Repository/VcsPackageFilter.php on line 279

Fatal error: Call to undefined method Composer\Package\Loader\ArrayLoader::parseLinks() in /home/daniele/.composer/vendor/fxp/composer-asset-plugin/Repository/VcsPackageFilter.php on line 279

I fixed this in my own environment a couple of days ago, but I don't remember what exactly I did.

Try removing the composer asset plugin first:

composer global remove fxp/composer-asset-plugin
sudo composer self-update
composer global require fxp/composer-asset-plugin
composer install