┌─────────┬────────────────────────────────────┬────────────────────────────────────┐ │ Escape  │                                    │                                    │ │Sequence │            Description             │              Meaning               │ ├─────────┼────────────────────────────────────┼────────────────────────────────────┤ │\"       │ <backslash> <quotation-mark>       │ <quotation-mark> character         │ ├─────────┼────────────────────────────────────┼────────────────────────────────────┤ │\/       │ <backslash> <slash>                │ <slash> character                  │ ├─────────┼────────────────────────────────────┼────────────────────────────────────┤ │\ddd     │ A <backslash> character followed   │ The character whose encoding is    │ │         │ by the longest sequence of one,    │ represented by the one, two, or    │ │         │ two, or three octal-digit          │ three-digit octal integer. Multi-  │ │         │ characters (01234567). If all of   │ byte characters require multiple,  │ │         │ the digits are 0 (that is,         │ concatenated escape sequences of   │ │         │ representation of the NUL          │ this type, including the leading   │ │         │ character), the behavior is        │ <backslash> for each byte.         │ │         │ undefined.                         │                                    │ ├─────────┼────────────────────────────────────┼────────────────────────────────────┤ │\c       │ A <backslash> character followed   │ Undefined                          │ │         │ by any character not described in  │                                    │ │         │ this table or in the table in the  │                                    │ │         │ Base Definitions volume of         │                                    │ │         │ POSIX.1‐2017, Chapter 5, File      │                                    │ │         │ Format Notation ('\\', '\a', '\b', │                                    │ │         │ '\f', '\n', '\r', '\t', '\v').     │                                    │ └─────────┴────────────────────────────────────┴────────────────────────────────────┘ A regular expression can be matched against a specific field or string by using one of the two regular expression matching operators, '~' and "!~". These operators shall interpret their right-hand operand as a regular expression and their left-hand operand as a string. If the regular expression matches the string, the '~' expression shall evaluate to a value of 1, and the "!~" expression shall evaluate to a value of 0. (The regular expression matching operation is as defined by the term matched in the Base Definitions volume of POSIX.1‐2017, Section 9.1, Regular Expression Definitions, where a match occurs on any part of the string unless the regular expression is limited with the <circumflex> or <dollar-sign> special characters.) If the regular expression does not match the string, the '~' expression shall evaluate to a value of 0, and the "!~" expression shall evaluate to a value of 1. If the right-hand operand is any expression other than the lexical token ERE, the string value of the expression shall be interpreted as an extended regular expression, including the escape conventions described above.  Note that these same escape conventions shall also be applied in determining the value of a string literal (the lexical token STRING), and thus shall be applied a second time when a string literal is used in this context.