Below are the exact commands I entered and exactly what happened when I followed your instructions. I did it as root. It worked fine. Sorry!
Maybe something below will help you. If not, my goto is often strace for a quick look at a problem like this before I try anything too complicated:
Using strace
strace /usr/local/bin/composer
Your commands and output
root@haze:~# curl -sS https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin --filename=composer
All settings correct for using Composer
Downloading 1.2.0...
Composer successfully installed to: /usr/local/bin/composer
Use it: php /usr/local/bin/composer
root@haze:~# /usr/local/bin/composer
Do not run Composer as root/super user! See https://getcomposer.org/root for details
______
/ ____/___ ____ ___ ____ ____ ________ _____
/ / / __ \/ __ `__ \/ __ \/ __ \/ ___/ _ \/ ___/
/ /___/ /_/ / / / / / / /_/ / /_/ (__ ) __/ /
\____/\____/_/ /_/ /_/ .___/\____/____/\___/_/
/_/
Composer version 1.2.0 2016-07-19 01:28:52
Usage:
command [options] [arguments]
Options:
-h, --help Display this help message
-q, --quiet Do not output any message
-V, --version Display this application version
--ansi Force ANSI output
--no-ansi Disable ANSI output
-n, --no-interaction Do not ask any interactive question
--profile Display timing and memory usage information
--no-plugins Whether to disable plugins.
-d, --working-dir=WORKING-DIR If specified, use the given directory as working directory.
-v|vv|vvv, --verbose Increase the verbosity of messages: 1 for normal output, 2 for more verbose output and 3 for debug
Available commands:
about Short information about Composer
archive Create an archive of this composer package
browse Opens the package's repository URL or homepage in your browser.
clear-cache Clears composer's internal package cache.
clearcache Clears composer's internal package cache.
config Set config options
create-project Create new project from a package into given directory.
depends Shows which packages cause the given package to be installed
diagnose Diagnoses the system to identify common errors.
dump-autoload Dumps the autoloader
dumpautoload Dumps the autoloader
exec Execute a vendored binary/script
global Allows running commands in the global composer dir ($COMPOSER_HOME).
help Displays help for a command
home Opens the package's repository URL or homepage in your browser.
info Show information about packages
init Creates a basic composer.json file in current directory.
install Installs the project dependencies from the composer.lock file if present, or falls back on the composer.json.
licenses Show information about licenses of dependencies
list Lists commands
outdated Shows a list of installed packages that have updates available, including their latest version.
prohibits Shows which packages prevent the given package from being installed
remove Removes a package from the require or require-dev
require Adds required packages to your composer.json and installs them
run-script Run the scripts defined in composer.json.
search Search for packages
self-update Updates composer.phar to the latest version.
selfupdate Updates composer.phar to the latest version.
show Show information about packages
status Show a list of locally modified packages
suggests Show package suggestions
update Updates your dependencies to the latest version according to composer.json, and updates the composer.lock file.
validate Validates a composer.json and composer.lock
why Shows which packages cause the given package to be installed
why-not Shows which packages prevent the given package from being installed
root@haze:~#
OS = Ubuntu 16.04
