I'd just use s/^(\d{4})$/$1_001/ 

~>perl -e '@id = (1234,"4323_003"); foreach ( @id ) { s/^(\d{4})$/$1_0
+01/; print $_, "\n"; }'
1234_001
4323_003

[download]

If the input needs to be checked, I'd do it separately (and before).

qq

In reply to Re: Variable assignment confusion by qq
in thread Variable assignment confusion by sweetblood

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