php error while installation of laravel

install mbstring?

sudo apt-get install php-mbstring

after placing above command

Reading package lists... Done Building dependency tree Reading state information... Done php-mbstring is already the newest version (1:7.0+44). The following package was automatically installed and is no longer required: ubuntu-core-launcher Use 'sudo apt autoremove' to remove it. 0 upgraded, 0 newly installed, 0 to remove and 3 not upgraded.

What is the version of PHP you're using?

php -v in your terminal

PHP 7.0.15-0ubuntu0.16.10.4 (cli) ( NTS ) Copyright (c) 1997-2017 The PHP Group Zend Engine v3.0.0, Copyright (c) 1998-2017 Zend Technologies with Zend OPcache v7.0.15-0ubuntu0.16.10.4, Copyright (c) 1999-2017, by Zend Technologies

Also, is mbstring listed if you use the command php -m ?

PHP Warning: PHP Startup: Unable to load dynamic library '/usr/lib/php/20151012/php_mbstring.dll'

Hm, you say you're on Ubuntu but mbstring.dll is a Windows dependency... which I think is weird :p

What you can try to do is:

1. Open the php.ini file (depending on your setup, I'm sure where it is in Ubuntu, but something like /etc/php/{ your php version }/php.ini)
2. Find the line that says ;extension=php_mbstring.dll
3. Uncomment (remove the ; at the beginning of the line).
4. Save, and restart your web server if necessary

yes i did

but stll not done

yup after committing ;extension=php_mbstring.dll line is worked

Good for you!