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Diffstat (limited to 'doc/bird.sgml')
| -rw-r--r-- | doc/bird.sgml | 49 |
1 files changed, 33 insertions, 16 deletions
diff --git a/doc/bird.sgml b/doc/bird.sgml index ea126fa2..c48b064c 100644 --- a/doc/bird.sgml +++ b/doc/bird.sgml @@ -1262,8 +1262,8 @@ this: <code> filter not_too_far -int var; { + int var; if defined( rip_metric ) then var = rip_metric; else { @@ -1292,9 +1292,9 @@ local variables. Recursion is not allowed. Function definitions look like this: <code> function name () -int local_variable; { - local_variable = 5; + int local_variable; + int another_variable = 5; } function with_parameters (int parameter) @@ -1303,16 +1303,19 @@ function with_parameters (int parameter) } </code> -<p>Unlike in C, variables are declared after the <cf/function/ line, but before -the first <cf/{/. You can't declare variables in nested blocks. Functions are -called like in C: <cf>name(); with_parameters(5);</cf>. Function may return -values using the <cf>return <m/[expr]/</cf> command. Returning a value exits -from current function (this is similar to C). +<p>Like in C programming language, variables are declared inside function body, +either at the beginning, or mixed with other statements. Declarations may +contain initialization. You can also declare variables in nested blocks, such +variables have scope restricted to such block. There is a deprecated syntax to +declare variables after the <cf/function/ line, but before the first <cf/{/. +Functions are called like in C: <cf>name(); with_parameters(5);</cf>. Function +may return values using the <cf>return <m/[expr]/</cf> command. Returning a +value exits from current function (this is similar to C). -<p>Filters are defined in a way similar to functions except they can't have +<p>Filters are defined in a way similar to functions except they cannot have explicit parameters. They get a route table entry as an implicit parameter, it is also passed automatically to any functions called. The filter must terminate -with either <cf/accept/ or <cf/reject/ statement. If there's a runtime error in +with either <cf/accept/ or <cf/reject/ statement. If there is a runtime error in filter, the route is rejected. <p>A nice trick to debug filters is to use <cf>show route filter <m/name/</cf> @@ -1682,7 +1685,8 @@ prefix and an ASN as arguments. <sect>Control structures <label id="control-structures"> -<p>Filters support two control structures: conditions and case switches. +<p>Filters support several control structures: conditions, for loops and case +switches. <p>Syntax of a condition is: <cf>if <M>boolean expression</M> then <m/commandT/; else <m/commandF/;</cf> and you can use <cf>{ <m/command1/; <m/command2/; @@ -1690,6 +1694,14 @@ else <m/commandF/;</cf> and you can use <cf>{ <m/command1/; <m/command2/; omitted. If the <cf><m>boolean expression</m></cf> is true, <m/commandT/ is executed, otherwise <m/commandF/ is executed. +<p>For loops allow to iterate over elements in compound data like BGP paths or +community lists. The syntax is: <cf>for [ <m/type/ ] <m/variable/ in <m/expr/ +do <m/command/;</cf> and you can also use compound command like in conditions. +The expression is evaluated to a compound data, then for each element from such +data the command is executed with the item assigned to the variable. A variable +may be an existing one (when just name is used) or a locally defined (when type +and name is used). In both cases, it must have the same type as elements. + <p>The <cf>case</cf> is similar to case from Pascal. Syntax is <cf>case <m/expr/ { else: | <m/num_or_prefix [ .. num_or_prefix]/: <m/statement/ ; [ ... ] }</cf>. The expression after <cf>case</cf> can be of any type which can be @@ -1702,16 +1714,21 @@ neither of the <cf/:/ clauses, the statements after <cf/else:/ are executed. <p>Here is example that uses <cf/if/ and <cf/case/ structures: <code> +if 1234 = i then printn "."; else { + print "not 1234"; + print "You need {} around multiple commands"; +} + +for int asn in bgp_path do { + printn "ASN: ", asn; + if asn < 65536 then print " (2B)"; else print " (4B)"; +} + case arg1 { 2: print "two"; print "I can do more commands without {}"; 3 .. 5: print "three to five"; else: print "something else"; } - -if 1234 = i then printn "."; else { - print "not 1234"; - print "You need {} around multiple commands"; -} </code> |