How do I connect PHP 7.x to Oracle database on Red

I am struggling to connect my PHP application to an Oracle database. I have tried multiple options over the last week with no success.

I have managed to install oci8 extension but the oci_connect function is not recognised.

Please assist.

RedHat Enterprise Linux 7.6
PHP: 7.3
Oracle: 12c

Having struggled for over a week to figure this out, here is a summary of what ultimately worked. I hope this helps somebody else.

These instructions apply to RedHat / CentOS Linux installations. My experience was that the instructions for RedHat / CentOS were slightly different to other Linux installations. AVOID the Oracle guidance... They did not help at all!

Step1: I followed the instructions on this excellent website to install PHP 7.3 and additional Remi rpm packages:https://tecadmin.net/install-php7-on-centos7/

Step 2: I then used the Remi repository (see step 1) to install the oci8 extension:

$ sudo yum --enablerepo=remi-php73 install php-oci8

Step 3: We now need to install the oracle instant client 18.3 packages. This is very nicely explained on this website: https://qiita.com/tkprof/items/2a4eb868f45fb5759110

$ cd /etc/yum.repos.d
$ sudo wget http://yum.oracle.com/public-yum-ol7.repo
$ sudo wget http://yum.oracle.com/RPM-GPG-KEY-oracle-ol7
$ sudo rpm --import RPM-GPG-KEY-oracle-ol7
$ sudo yum-config-manager --enable ol7_oracle_instantclient
$ sudo yum install oracle-instantclient18.3-basic
$ sudo yum install oracle-instantclient18.3-devel
$ sudo yum install oracle-instantclient18.3-jdbc
$ sudo yum install oracle-instantclient18.3-sqlplus
$ sudo yum list oracle-instantclient*

Step 4: The oracle files have been created in /usr/lib/oracle/18.3 We now need to create a symlink so that the oracle files are included when the server is running:

$ sudo sh -c "echo /usr/lib/oracle/18.3/client64/lib > /etc/ld.so.conf.d/oracle-instantclient.conf"
$ sudo ldconfig

Step 5: Restart the server

 $ sudo systemctl stop httpd
 $ sudo systemctl start httpd

Step 6: We can now create a simple php file that tests the connection to Oracle:

<?php     
$conn = oci_connect("username", "password", "//url/SID");

if (!$conn) {
    echo "oci8 working! However the following errors occurred: <br>";
    $m = oci_error();
    echo $m['message'], "\n";
    exit;
} else {
    print "Connected to Oracle!";
}
// Close the Oracle connection
oci_close($conn);

If you get a system error then the installation has not worked.