use strict;
my $str = '![Screenshot_20210618-090636](/uploads/7afe1f092f836d61a5fa008cf9a0c991/Screenshot_20210618-090636.jpg)
![screenshot](uploads/9d461c7a3fd8cffb4c7a84c1948f345f/bootloader.jpg)';
my $regex = qr/\!\[.+?\]\((.+?)\)/mp;
my $subst = '<img src="$1" width="300">';
my $result = $str =~ s/$regex/$subst/rg;
print "The result of the substitution is' $result\n";
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Perl, please visit: http://perldoc.perl.org/perlre.html