#!/bin/perl -p

# basic substitution

# processing the field method is easy
s/((\$\w+)->field\b/$1\->\{field\}/g;
# the set_field method has an argument, capture it
s/s/(\$\w+)->set_field\(([^)]*)\)/$1\->\{field\}= $2/g


##</code><code>##

#!/bin/perl -p
BEGIN { $FIELD="field1|field2|field3"; }
s/(\$\w+(?:\[\d\])?)->($FIELD)\b(?!\()/$1\->\{$2\}/g;
s/(\$\w+(?:\[\d\])?)->set_($FIELD)\(([^)]*)\)/$1\->\{$2\}= $3/g;