inline_svg.php

<?php
function read_project_svg_assets( $directory ) {
	$files = [];
	$path = get_template_directory() . '/library/assets/*.svg';
	foreach ( glob( $path ) as $filename ) {
		$path_parts = pathinfo( $filename );
		$files[] = $path_parts['filename'];
	}
	$svgs = [];
	foreach ( $files as $svg_name ) {
		$file = sprintf( '%s/%s/%s.svg', 
		esc_url( get_template_directory_uri() ), 
		esc_attr( $directory ), 
		esc_attr( $svg_name )
	);
		$svgs[ $svg_name ] = file_get_contents( $file );
	}

	return $svgs;
}

function inline_svg( $svg_name, $directory = 'assets' ) {

	$svgs = get_transient( 'stored_svg_assets' );

	if ( false === $svgs ) {
		$svgs = read_project_svg_assets( $directory );
		set_transient( 'stored_svg_assets', $svgs, 60 * 60 * 24 );
	}
	return $svgs[$svg_name];
}

// to use simply call inline_svg
inline_svg( 'facebook' );
//Alternately. If your svgs are not in a folder called 'assets' in the root of your project
//you can pass that location too.
inline_svg( 'facebook', 'library/svgs' );