Create 4. Filtering.md

Author: HuyPham01

Bash-shell/4. Filtering.md

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+Sử dụng các ký tự đặc biệt trong các bộ lọc, tìm kiếm
+
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+|Symbol |Result|
+|---------|--------|
+|.| Matches any character.|
+|#|Matches zero or more instances of the preceding character.|
+|+|Matches one or more instances of the preceding character.|
+|[] |Matches any of the characters within the brackets.||
+|`|`|**OR**  operator; (www|ftp) matches either “www” or “ftp”.|
+|^|Matches the beginning of a line.|
+|$|Matches the end of a line.|
+|\ |Escapes the following character. Since  `.`  matches any character, to match a literal period you would need to use  `\.`. |