Dell N1100-ON Reference Manual page 1250

Up to 128 AS path access lists can be configured, with up to 64 statements
each. To enter the question mark within a regular expression, first enter
CTRL-V to prevent the CLI from interpreting the question mark as a request
for help.
Special Character/Symbol
asterisk
brackets
caret
dollar sign
hyphen
period
plus sign
question mark
underscore
Command History
Introduced in version 6.2.0.1 firmware.
Example
In the following example, the router is configured to reject routes received
from neighbor 172.20.1.1 with an AS path that indicates the route originates
in or passes through AS 100.
console(config)# ip as-path access-list 1 deny _100_
console(config)# ip as-path access-list 1 deny ^100$
console(config)# router bgp 1
Behavior
* Matches zero or more sequences of the
pattern.
[] Designates a range of single-character
patterns.
^ Matches the beginning of the input
string.
$ Matches the end of the input string.
- Separates the end points of a range.
. Matches any single character, including
white space.
+ Matches 1 or more sequences of the
pattern.
? Matches 0 or 1 occurrences of the
pattern.
_ 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.
Layer 3 Routing Commands
1250