Para obtener información sobre la forma en que es compilada una expresión regular
y como se produce el proceso de matching podemos usar la opción
'debug' del módulo re. La versión de Perl 5.10 da una información
algo mas legible que la de las versiones anteriores:
pl@nereida:~/Lperltesting$ perl5_10_1 -wde 0
Loading DB routines from perl5db.pl version 1.32
Editor support available.
Enter h or `h h' for help, or `man perldebug' for more help.
main::(-e:1): 0
DB<1> use re 'debug'; 'astr' =~ m{[sf].r}
Compiling REx "[sf].r"
Final program:
1: ANYOF[fs][] (12)
12: REG_ANY (13)
13: EXACT <r> (15)
15: END (0)
anchored "r" at 2 (checking anchored) stclass ANYOF[fs][] minlen 3
Guessing start of match in sv for REx "[sf].r" against "astr"
Found anchored substr "r" at offset 3...
Starting position does not contradict /^/m...
start_shift: 2 check_at: 3 s: 1 endpos: 2
Does not contradict STCLASS...
Guessed: match at offset 1
Matching REx "[sf].r" against "str"
1 <a> <str> | 1:ANYOF[fs][](12)
2 <as> <tr> | 12:REG_ANY(13)
3 <ast> <r> | 13:EXACT <r>(15)
4 <astr> <> | 15:END(0)
Match successful!
Freeing REx: "[sf].r"
Si se usa la opción debug de re con
objetos expresión regular, se obtendrá información durante el proceso de
matching:
DB<3> use re 'debug'; $re = qr{[sf].r}
Compiling REx "[sf].r"
Final program:
1: ANYOF[fs][] (12)
12: REG_ANY (13)
13: EXACT <r> (15)
15: END (0)
anchored "r" at 2 (checking anchored) stclass ANYOF[fs][] minlen 3
DB<4> 'astr' =~ $re
Guessing start of match in sv for REx "[sf].r" against "astr"
Found anchored substr "r" at offset 3...
Starting position does not contradict /^/m...
start_shift: 2 check_at: 3 s: 1 endpos: 2
Does not contradict STCLASS...
Guessed: match at offset 1
Matching REx "[sf].r" against "str"
1 <a> <str> | 1:ANYOF[fs][](12)
2 <as> <tr> | 12:REG_ANY(13)
3 <ast> <r> | 13:EXACT <r>(15)
4 <astr> <> | 15:END(0)
Match successful!