If you want * in regular expressions to act as a wildcard, you need to use. However, in regular expressions, * is a modifier, meaning that it only applies to the character or group preceding it. In the console, * is part of a glob construct, and just acts as a wildcard (for instance ls *.log will list all files that end in. * in a regular expression is not exactly the same as * in the console. If you want to just match abc, you could just say grep 'abc' myFile. * - the dot means any character ( within certain guidelines). For example, ¬A is a regular expression matching the letter A at the beginning of a line.
Regular expressions can be made up of normal characters or special characters. grep understands three different versions of regular expression syntax: basic (BRE), extended (ERE), and Perl-compatible (PCRE). If you want to match anything, you need to say. grep and sed accept basic regular expressions, but will accept extended regular expressions if the E option is used. Regular expressions are constructed analogously to arithmetic expressions, by using various operators to combine smaller expressions. *abc*/ matches a string containing ab and zero or more c's (because the second * is on the c the first is meaningless because there's nothing for it to repeat). The asterisk is just a repetition operator, but you need to tell it what you repeat. Will match a string that contains abc followed by def with something optionally in between.
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