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| Related Syntax | |||||||||
| operator | take | ||||||||
Return type: String A string that is the part of the source matched by the pattern.
Returns:
Syntax
source take pattern
The take operator returns a string that is the data from the current source matched by a specified pattern.
You can use take to perform substring operations. The following code uses take to grab the first 4 characters of a string:
process
output "abcdefghijklm" take any{4}
This program will output "ABCD".
You can use take with any OmniMark source and as part of a nested pattern matching operation. The following code uses take to select a string from #current-input:
process
local stream area-code
using input as "My telephone number is (123) 555-7890"
repeat scan #current-input
match any** lookahead "("
set area-code to #current-input take ("(" digit{3} ")")
again
output area-code
Notice that the pattern used in a take must be a simple pattern. If you need more than one pattern element in a take, you must wrap the whole pattern in parentheses. Thus the take pattern in the code above is written ("(" digit{2} ")").
It is an error if the pattern in a take does not match. The following program includes an error in the data that causes the take pattern not to match. This results in a program error, which is caught and processed by the program:
process
local stream area-code
using input as "My telephone number is (1523) 555-7890"
repeat scan #current-input
match any** lookahead "("
set area-code to #current-input take ("(" digit{3} ")")
again
output area-code
catch #program-error code c
do when c = 6132
output "Area code not found"
else
rethrow
done
If you want to ensure that a take operation always succeeds, write your pattern so that it can match zero characters. In the following program, this is achieved by adding a "?" to the end of the take pattern. Since any pattern with a ? or * occurrence indicator can match zero times, such a pattern will always match (though it may match zero characters):
process
local stream area-code
using input as "My telephone number is (1523) 555-7890"
repeat scan #current-input
match any** lookahead "("
set area-code to #current-input take ("(" digit{3} ")")?
again
output area-code
Since the data error still exists, the take pattern will return zero characters and the take operator will return a zero-length string. The program will therefore output nothing.
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Related Syntax drop |
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