From e1e893d3b98fccf819bd9b2d3a1ea4fb1cbb3627 Mon Sep 17 00:00:00 2001
From: "Kevin P. Fleming" <kpfleming@digium.com>
Date: Wed, 20 Apr 2005 14:46:54 +0000
Subject: [PATCH] enhance documentation for string chopping (bug #4049)
git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@5486 65c4cc65-6c06-0410-ace0-fbb531ad65f3
---
doc/README.variables | 51 +++++++++++++++++++++++++++++++-------------
1 file changed, 36 insertions(+), 15 deletions(-)
diff --git a/doc/README.variables b/doc/README.variables
index 3d438f8c3f..050bd1285d 100755
--- a/doc/README.variables
+++ b/doc/README.variables
@@ -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=${EXTEN:1})
+
+Assuming we've dialed 918005551234, the value saved to the 'number' variable
+would be 18005551234. This is useful in situations when we require users to
+dial a number to access an outside line, but do not wish to pass the first
+digit.
+
+If you use a negative offset number, Asterisk starts counting from the end
+of the string and then removes everything before the new position. The following
+example will save the numbers 1234 to the 'number' variable, still assuming
+we've dialed 918005551234.
+
+ ;Remove everything before the last four digits of the dialed string
+ exten => _9X.,1,SetVar(number=${EXTEN:-4})
-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=${STRING:5:2})
+We can also limit the number of characters from our offset position that we
+wish to use. This is done by appending a second colon and length value to the
+variable name. The following example will save the numbers 555 to the 'number'
+variable.
-You can also count from the end of the string by giving a negative
-position:
+ ;Only save the middle numbers 555 from the string 918005551234
+ exten => _9X.,1,SetVar(number=${EXTEN:5:3})
- ;Use the two first of the three last characters in the account code
- exten => 4500,4,setvar(acc=${ACCOUNTCODE:-3:2})
+The length value can also be used in conjunction with a negative offset. This
+may be useful if the length of the string is unknown, but the trailing digits
+are. The following example will save the numbers 555 to the 'number' variable,
+even if the string starts with more characters than expected (unlike the
+previous example).
-Or
- ;Use the last three digits of the phone number
- exten => 6112,4,goto(${EXTEN:-3},1)
+ ;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:
---------------------------
--
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