Install composer v1.x and v2.x simultaneously

composer.sh

#!/bin/sh

EXPECTED_CHECKSUM="$(wget -q -O - https://composer.github.io/installer.sig)"
php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"
ACTUAL_CHECKSUM="$(php -r "echo hash_file('sha384', 'composer-setup.php');")"

if [ "$EXPECTED_CHECKSUM" != "$ACTUAL_CHECKSUM" ]
then
    >&2 echo 'ERROR: Invalid installer checksum'
    rm composer-setup.php
    exit 1
fi

# Version 1
php composer-setup.php --quiet --install-dir=/usr/local/bin/ --filename=composer --version=1.10.22

# Version 2 - If you want to install simultaneously
php composer-setup.php --quiet --install-dir=/usr/local/bin/ --filename=composer2

# Check the versions if it is installed correctly
composer --version

# Uncomment this if you want to check composer2 version.
# composer2 --version

RESULT=$?
rm composer-setup.php
exit $RESULT