| Regular expressions {GCDkit} | R Documentation | 
Implementation of regular expressions in the searching patterns.
Many enquiries in the GCDkit employ regular expressions. This is a quite powerful searching mechanism more familiar to people working in Unix. Put in simple terms, most characters, including all letters and digits, are regular expressions that match themselves. However, metacharacters with a special meaning ('?' '+' '{' '}' '|' '(' ')') must be preceded by a backslash.
| Regular expression | Matches | 
| . | Any character | 
| ^ | Beginning of the expression | 
| \$ | End of the expression | 
| [ ] | Any of the characters given in square brackets | 
| [m-n] | Any character in the range given by mandn | 
A subexpression is a regular expression enclosed in '\(' and '\)'. Two such subexpressions may be joined by the infix operator '|' (logical or); the resulting regular expression matches any string matching either of them. For instance:
\(South\)|\(North\)Uist
yields both
South Uist and North Uist.
A regular expression may be followed by one of several repetition operators:
| Repetition operator | The preceding item will be matched | 
| ? | At most once (i.e. is optional) | 
| * | Zero or more times | 
| + | One or more times | 
| {n} | Exactly ntimes | 
| {n,} | At least n times | 
| {n,m} | At least ntimes, but not more thanmtimes | 
Vojtěch Janoušek, vojtech.janousek@geology.cz
    ## Not run: 
        # Subset by label
        The searched field corresponds to localities with the following levels: 
        Mull, Rum, Skye, Coll, Colonsay, Hoy, Westray, Sanday, 
        Stronsay, Tiree, Islay
        Search pattern = ol       
        Coll, Colonsay
        Search pattern = n.a      
        Colonsay, Sanday, Stronsay
        Search pattern = ^S       
        Skye, Sanday, Stronsay
        Search pattern = e$       
        Skye, Tiree
        Search pattern = [ds]ay     
        Colonsay, Sanday, Stronsay
        Search pattern = [p-s]ay
        Colonsay, Westray, Stronsay
        Search pattern = ol|oy    
        Coll, Colonsay, Hoy
        Search pattern = l{2}   
        Mull, Coll
        # Subset by sample name
        The sample names are: Bl-1, Bl-3, Koz-1, Koz-2, Koz-5, Koz-11, 
        KozD-1, Ri-1.
        Search pattern = oz-[1-3]    
        Koz-1, Koz-2, Koz-11
        Search pattern = oz-|Bl- 
        Bl-1, Bl-2, Bl-3, Koz-1, Koz-2, Koz-5, Koz-11
    
## End(Not run)