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[]defines a range of characters..matches any character.\is used to escape the following character when that character is a special character. So, for example, a regular expression that found '.com' would be\\.combecause.is a special character that matches any character.\dmatches any single digit.\wmatches any part of word character (equivalent to[A-Za-z0-9]).\smatches any space, tab, or newline.^asserts the position at the start of the line. So what you put after it will only match if they are the first characters of a line.$asserts the position at the end of the line. So what you put before it will only match if they are the last characters of a line.\badds a word boundary. Putting this either side of a stops the regular expression matching longer variants of words.*matches the preceding element zero or more times. For example,ab*cmatches 'ac', 'abc', 'abbbc', etc.+matches the preceding element one or more times. For example,ab+cmatches 'abc', 'abbbc' but not 'ac'.?matches when the preceding character appears zero or one time.{VALUE}matches the preceding character the number of times define by VALUE; ranges can be specified with the syntax{VALUE,VALUE}.|means or.