BGP regular expressions

sh ip bgp regexp {pattern}: Will displays the result of the RegEx
* [0-9]*: All routes from this AS
^[0-9]*$: This AS only
_.*: Matches everything [permit any/all] [a space and anything]
_100_: Match any route going through AS100
_100 200_: Match any route passed through 100 and 200
_100$: Match any route originated in AS100
^100$: Match only routes originated in AS100 that did not pass through any other AS
^100_: Match only routes transiting directly connected AS100, anything else behind
^100 .*: Match only routes received from AS100 or 1000..., anything else behind
^$ Match only routes originated from this AS
.*: Match anything [usually at end as: permit .*]
( .*): matches a space plus a AS
( .*)*: matches a space plus a AS or a null string
?: To type ?: either Ctrl-V or Esc-Q

.: Matches any single character, including white space.
*: Matches 0 or more sequences of the pattern.
+: Matches 1 or more sequences of the pattern.
?: Matches 0 or 1 occurrences of the pattern.
^: Matches the beginning of the input string.
$: Matches the end of the input string.
_: Matches a comma (,), left brace ({), right brace (}), left parenthesis, right parenthesis, the beginning of the input string, the end of the input string, or a space.
[]: Designates a range of single-character patterns.
-: Separates the end points of a range.
(): (Border Gateway Protocol (BGP) specific) Designates a group of characters as the name of a confederation.

^_250.*[0-9]$: 1 AS next away
^250_[0-9]*$: 1 AS next away, 250 = connected + next away [or none next away]

^250_(.+_)*888$: Originated by 888, connected to 250 and anything in between
^250(_.+)_*888$: Originated by 888, connected to 250 and anything in between

 route-map test permit 10   match as-path 1
 !
 ip as-path access-list 1 permit ^651..$

This will only match if THE routes come from an AS that is between 651 to 65199