Wikipedia defines a regular expression as “a sequence of characters that specifies a match pattern in text”.<\/p>\n
Another way is just to think of it as a way of describing text.<\/p>\n
For example, a UK number plate currently has the format of 2 letters, followed by 2 numbers, followed by 3 letters. As a regular expression this can be written as:<\/p>\n
[A-Z]{2}[0-9]{2}[A-Z]{3}<\/p>\n
So this would match the string AB12CDE but would not match AB1CDE<\/p>\n
Strangely this would also match ABC12DEFG because it contains the correct pattern (BC12DEF). If you want to exclude such strings then you can put a ^ at the start and a $ at the end:<\/p>\n
^[A-Z]{2}[0-9]{2}[A-Z]{3}$<\/p>\n
^ is a token for the start of a string and $ is a token for the end of the string.<\/p>\n
[] is used to specify a set of characters or a range…<\/p>\n
[a-zA-Z] means any lower or upper case character
\n[0-5] means any digit in the set 0, 1, 2, 3, 4, 5 and is the same as [012345]
\n[a6gW] means any character in the set a, 6, g or W<\/p>\n
{} is used to specify the number of times the previous token should be repeated, {N} just means N times but {N, M} means between N and M times (inclusive). You can also use the simple + for 1 or more or * for 0 or more (subtle difference!).<\/p>\n
e.g [A-Z]+[0-9]+[A-Z]+ would match ABC123DEF but would not match ABC123, on the other hand [A-Z]+[0-9]+[A-Z]* would match both.<\/p>\n
There are a few short cuts such as \\d to represent [0-9] but these can vary depending on whether you’re working in perl or java.<\/p>\n
BardecodeFiler uses regular expressions in the Reformat Table, which is a way of changing the information in a barcode into a file name. One extra concept you need to understand to use this is grouping using ().<\/p>\n
In our original number plate example you could divide it into 3 groups:<\/p>\n
^([A-Z]{2})([0-9]{2})([A-Z]{3})$<\/p>\n
So for the string AB12CDE this would mean that AB was the first group, 12 the second and CDE the third. <\/p>\n
You now have the power to pull a string apart and put it back together in a different order.<\/p>\n
Back to BardecodeFiler and the Reformat table – it has a number of rows and each row has a left side and a right side. The left side is a regular expression and the right side is the new format where {1} is a token for group 1, {2} for group 2 etc.<\/p>\n
For example, say we want to rewrite AB12CDE as CDE12AB<\/p>\n
Left side: ^([A-Z]{2})([0-9]{2})([A-Z]{3})$
\nRight side: {3}{2}{1}<\/p>\n","protected":false},"excerpt":{"rendered":"
Wikipedia defines a regular expression as “a sequence of characters that specifies a match pattern in text”. Another way is just to think of it as a way of describing text. For example, a UK number plate currently has the format of 2 letters, followed by 2 numbers, followed by 3 letters. As a regular<\/p>\n