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enhance documentation for string chopping (bug #4049)

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git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@5486 65c4cc65-6c06-0410-ace0-fbb531ad65f3
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Kevin P. Fleming
2005-04-20 14:46:54 +00:00
parent f933db8c24
commit e1e893d3b9
1 changed files with 36 additions and 15 deletions
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51
doc/README.variables
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@@ -69,28 +69,49 @@ _______________________________
REMOVING CHARACTERS FROM STRING
-------------------------------
If you want to remove the first N characters from a string, you just
add a colon and the number of characters, like
The format for removing characters from a variable can be expressed as:
${variable_name[:offset[:length]]}
If you want to remove the first N characters from the string assigned
to a variable, simply append a colon and the number of characters to
remove from the beginning of the string to the variable name.
;Remove the first character of extension, save in "number" variable
exten => _9X.,1,setvar(number=${EXTEN:1})
exten => _9X.,1,SetVar(number=${EXTEN:1})
A second colon limits the number of characters used from the original
string.
;Strip five characters from the start of string, use only two
; (character 6 and 7 in the original string)
exten => 1000,4,setvar(skrep=${STRING:5:2})
Assuming we've dialed 918005551234, the value saved to the 'number' variable
would be 18005551234. This is useful in situations when we require users to
dial a number to access an outside line, but do not wish to pass the first
digit.
You can also count from the end of the string by giving a negative
position:
If you use a negative offset number, Asterisk starts counting from the end
of the string and then removes everything before the new position. The following
example will save the numbers 1234 to the 'number' variable, still assuming
we've dialed 918005551234.
;Use the two first of the three last characters in the account code
exten => 4500,4,setvar(acc=${ACCOUNTCODE:-3:2})
;Remove everything before the last four digits of the dialed string
exten => _9X.,1,SetVar(number=${EXTEN:-4})
Or
;Use the last three digits of the phone number
exten => 6112,4,goto(${EXTEN:-3},1)
We can also limit the number of characters from our offset position that we
wish to use. This is done by appending a second colon and length value to the
variable name. The following example will save the numbers 555 to the 'number'
variable.
;Only save the middle numbers 555 from the string 918005551234
exten => _9X.,1,SetVar(number=${EXTEN:5:3})
The length value can also be used in conjunction with a negative offset. This
may be useful if the length of the string is unknown, but the trailing digits
are. The following example will save the numbers 555 to the 'number' variable,
even if the string starts with more characters than expected (unlike the
previous example).
;Save the numbers 555 to the 'number' variable
exten => _9X.,1,SetVar(number=${EXTEN:-7:3})
If a negative length value is entered, it is ignored and Asterisk will match
to the end of the string.
___________________________
EXPRESSIONS:
---------------------------