Example: flutter postcode regex
"GB", "GIR[ ]?0AA|((AB|AL|B|BA|BB|BD|BH|BL|BN|BR|BS|BT|CA|CB|CF|CH|CM|CO|CR|CT|CV|CW|DA|DD|DE|DG|DH|DL|DN|DT|DY|E|EC|EH|EN|EX|FK|FY|G|GL|GY|GU|HA|HD|HG|HP|HR|HS|HU|HX|IG|IM|IP|IV|JE|KA|KT|KW|KY|L|LA|LD|LE|LL|LN|LS|LU|M|ME|MK|ML|N|NE|NG|NN|NP|NR|NW|OL|OX|PA|PE|PH|PL|PO|PR|RG|RH|RM|S|SA|SE|SG|SK|SL|SM|SN|SO|SP|SR|SS|ST|SW|SY|TA|TD|TF|TN|TQ|TR|TS|TW|UB|W|WA|WC|WD|WF|WN|WR|WS|WV|YO|ZE)(\d[\dA-Z]?[ ]?\d[ABD-HJLN-UW-Z]{2}))|BFPO[ ]?\d{1,4}"
"JE", "JE\d[\dA-Z]?[ ]?\d[ABD-HJLN-UW-Z]{2}"
"GG", "GY\d[\dA-Z]?[ ]?\d[ABD-HJLN-UW-Z]{2}"
"IM", "IM\d[\dA-Z]?[ ]?\d[ABD-HJLN-UW-Z]{2}"
"US", "\d{5}([ \-]\d{4})?"
"CA", "[ABCEGHJKLMNPRSTVXY]\d[ABCEGHJ-NPRSTV-Z][ ]?\d[ABCEGHJ-NPRSTV-Z]\d"
"DE", "\d{5}"
"JP", "\d{3}-\d{4}"
"FR", "\d{2}[ ]?\d{3}"
"AU", "\d{4}"
"IT", "\d{5}"
"CH", "\d{4}"
"AT", "\d{4}"
"ES", "\d{5}"
"NL", "\d{4}[ ]?[A-Z]{2}"
"BE", "\d{4}"
"DK", "\d{4}"
"SE", "\d{3}[ ]?\d{2}"
"NO", "\d{4}"
"BR", "\d{5}[\-]?\d{3}"
"PT", "\d{4}([\-]\d{3})?"
"FI", "\d{5}"
"AX", "22\d{3}"
"KR", "\d{3}[\-]\d{3}"
"CN", "\d{6}"
"TW", "\d{3}(\d{2})?"
"SG", "\d{6}"
"DZ", "\d{5}"
"AD", "AD\d{3}"
"AR", "([A-HJ-NP-Z])?\d{4}([A-Z]{3})?"
"AM", "(37)?\d{4}"
"AZ", "\d{4}"
"BH", "((1[0-2]|[2-9])\d{2})?"
"BD", "\d{4}"
"BB", "(BB\d{5})?"
"BY", "\d{6}"
"BM", "[A-Z]{2}[ ]?[A-Z0-9]{2}"
"BA", "\d{5}"
"IO", "BBND 1ZZ"
"BN", "[A-Z]{2}[ ]?\d{4}"
"BG", "\d{4}"
"KH", "\d{5}"
"CV", "\d{4}"
"CL", "\d{7}"
"CR", "\d{4,5}|\d{3}-\d{4}"
"HR", "\d{5}"
"CY", "\d{4}"
"CZ", "\d{3}[ ]?\d{2}"
"DO", "\d{5}"
"EC", "([A-Z]\d{4}[A-Z]|(?:[A-Z]{2})?\d{6})?"
"EG", "\d{5}"
"EE", "\d{5}"
"FO", "\d{3}"
"GE", "\d{4}"
"GR", "\d{3}[ ]?\d{2}"
"GL", "39\d{2}"
"GT", "\d{5}"
"HT", "\d{4}"
"HN", "(?:\d{5})?"
"HU", "\d{4}"
"IS", "\d{3}"
"IN", "\d{6}"
"ID", "\d{5}"
"IL", "\d{5}"
"JO", "\d{5}"
"KZ", "\d{6}"
"KE", "\d{5}"
"KW", "\d{5}"
"LA", "\d{5}"
"LV", "\d{4}"
"LB", "(\d{4}([ ]?\d{4})?)?"
"LI", "(948[5-9])|(949[0-7])"
"LT", "\d{5}"
"LU", "\d{4}"
"MK", "\d{4}"
"MY", "\d{5}"
"MV", "\d{5}"
"MT", "[A-Z]{3}[ ]?\d{2,4}"
"MU", "(\d{3}[A-Z]{2}\d{3})?"
"MX", "\d{5}"
"MD", "\d{4}"
"MC", "980\d{2}"
"MA", "\d{5}"
"NP", "\d{5}"
"NZ", "\d{4}"
"NI", "((\d{4}-)?\d{3}-\d{3}(-\d{1})?)?"
"NG", "(\d{6})?"
"OM", "(PC )?\d{3}"
"PK", "\d{5}"
"PY", "\d{4}"
"PH", "\d{4}"
"PL", "\d{2}-\d{3}"
"PR", "00[679]\d{2}([ \-]\d{4})?"
"RO", "\d{6}"
"RU", "\d{6}"
"SM", "4789\d"
"SA", "\d{5}"
"SN", "\d{5}"
"SK", "\d{3}[ ]?\d{2}"
"SI", "\d{4}"
"ZA", "\d{4}"
"LK", "\d{5}"
"TJ", "\d{6}"
"TH", "\d{5}"
"TN", "\d{4}"
"TR", "\d{5}"
"TM", "\d{6}"
"UA", "\d{5}"
"UY", "\d{5}"
"UZ", "\d{6}"
"VA", "00120"
"VE", "\d{4}"
"ZM", "\d{5}"
"AS", "96799"
"CC", "6799"
"CK", "\d{4}"
"RS", "\d{6}"
"ME", "8\d{4}"
"CS", "\d{5}"
"YU", "\d{5}"
"CX", "6798"
"ET", "\d{4}"
"FK", "FIQQ 1ZZ"
"NF", "2899"
"FM", "(9694[1-4])([ \-]\d{4})?"
"GF", "9[78]3\d{2}"
"GN", "\d{3}"
"GP", "9[78][01]\d{2}"
"GS", "SIQQ 1ZZ"
"GU", "969[123]\d([ \-]\d{4})?"
"GW", "\d{4}"
"HM", "\d{4}"
"IQ", "\d{5}"
"KG", "\d{6}"
"LR", "\d{4}"
"LS", "\d{3}"
"MG", "\d{3}"
"MH", "969[67]\d([ \-]\d{4})?"
"MN", "\d{6}"
"MP", "9695[012]([ \-]\d{4})?"
"MQ", "9[78]2\d{2}"
"NC", "988\d{2}"
"NE", "\d{4}"
"VI", "008(([0-4]\d)|(5[01]))([ \-]\d{4})?"
"PF", "987\d{2}"
"PG", "\d{3}"
"PM", "9[78]5\d{2}"
"PN", "PCRN 1ZZ"
"PW", "96940"
"RE", "9[78]4\d{2}"
"SH", "(ASCN|STHL) 1ZZ"
"SJ", "\d{4}"
"SO", "\d{5}"
"SZ", "[HLMS]\d{3}"
"TC", "TKCA 1ZZ"
"WF", "986\d{2}"
"XK", "\d{5}"
"YT", "976\d{2}"