Regular-Expression

.          Any single character, including white space.
[]         Any character listed between the brackets.
[^]        Any character except those listed between the brackets. (The caret is placed before the sequence of literals.)
-          (Hyphen) Any character in the range between the two literals separated by the hyphen.
?          Zero or one instances of the character or pattern.
*          Zero or more instances of the character or pattern.
+          One or more instances of the character or pattern.
^          Start of a line.
$          End of a line.
|          Either of the literals separated by the metacharacter.
_         (Underscore) A comma, the beginning of the line, the end of the line, or a space.

Sample

ip as-path access-list 10 permit .*　・・・　全てのルート
ip as-path access-list 11 permit ^$　・・・　ローカルで生成されたルート
ip as-path access-list 12 permit ^100_　・・・　AS100から学習したルート
ip as-path access-list 13 permit _100$　・・・　AS100で生成されたルート
ip as-path access-list 14 permit _100_　・・・　AS100を経路に含んでいるルート
ip as-path access-list 15 permit ^[0-9]+$　・・・　直接接続されているASから学習したルート
ip as-path access-list 16 permit ^[0-9]+(_[0-9])?$　・・・　直接接続されているAS or その配下のASから学習したルート