* as previously mentioned - the dot is a wildcard character, and the star, when modifying the dot, means find one or more dot ie. If you want * in regular expressions to act as a wildcard, you need to use. Now I execute the same commands for these 3 files, lets see what happen. echo abc > file1 echo abc > file2 echo abcc > file3. Therefore, the output highlights the following results: if. I summarize other answers, and make these examples to understand how the regex and glob work. The result shows all instances where the letter i appears followed by an f in the. The regex searches for the character string. However, in regular expressions, * is a modifier, meaning that it only applies to the character or group preceding it. Run the following command to test how grep regex works: grep if. 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 grep command is handy when searching through large log files. When it finds a match, it prints the line with the result. The text search pattern is called a regular expression. * - the dot means any character ( within certain guidelines). Grep is a Linux / Unix command-line tool used to search for a string of characters in a specified file. If you want to match anything, you need to say. *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). grep -x -f A.txt B.txt EDIT: If you don't want grep's regex capabilities and need to treat search pattern as fixed-strings then use -F switch as: grep -xF -f A.txt B.txt -x, -line-regexp Only input lines selected against an entire fixed string or regular expression are considered to be matching lines. Grep searches the named input FILEs (or standard input if no files are named, or the file name is given) for lines containing a match to the given PATTERN. 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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