Three ways to do this, really.
Create an alias in .bashrc
to always run composer with the corresponding version
Something like alias ncomposer=`/path/to/php /path/to/composer.phar `
Specify the path to PHP version inside composer.phar
itself
This is specified at the start of the file: #!/path/to/php php
. Then composer should run with composer.phar
NB! The line will disappear upon self-update, so it’s not a reliable solution.
Move up the path with the newest PHP version
If you place C:\nginx\php
first, it should be used by default when using composer.
Hope this helps!