To perform a multi-line edit in PERL command line mode along with using /s or /m quantifier, a switch needs to be passed to read the entire file in slurp mode.
The default mode in command line is to read a file line by line, but by adding -0777 switch it can be read as a single string
This is equivalent to writing $/ = undef (modifying the end of line indicator)
e.g.:
perl -0777 -p -i -e "s/\{.*?\}/Replaced braces/sg" file_name
Note:
1. Read the doc below for more info on the switch.
http://perldoc.perl.org/perlrun.html#*-0*[_octal/hexadecimal_]
2. Range operator can be another substitute ( .. )
if (/start_string/ .. /end_string/) ...