2. What is grep ?  % man grep  DESCRIPTION  The grep utility searches text files for a pattern and prints all lines that contain that pattern. It uses a compact non- deterministic algorithm.  Can search either a specified file or standard input  Be careful: certain characters such as $, *, [, ^, |, (, ), and \ are also meaningful to the shell.

3. grep options pattern input_file_names  Other variants of grep  fgrep – “fixed grep” (also known as “fast grep”) –does not support regular expressions (uses fixed strings).  egrep – supports the extended set +, ?, |, and ( ) – supports some metacharacters, but not others such as \(, \), \n, \ A metacharacter is a character that has a special meaning to a computer program, such as a shell interpreter or a regular expression engine. It is therefore safest to enclose the pattern list in single quotes (‘... ‘) to avoid confusion.

4. Useful grep options  -i or --ignore-case  - v or --invert-match //Selects non-matching lines  -w // Select only those lines containing matches that form whole words.  -c //Prints only a count of the lines that contain the pattern.  -n //Precede each line by its line number in the file (first line is 1). Many more advanced options are available in UNIX Resource #3 on course website or by checking man grep.

5. Examples The file users contains 18 lines. Shown are examples of the results from combining multiple grep options.

6. Examples (Cont’d)  % grep -i -w main *  search files in the current working directory for the word main, any case  % who | grep kc498  send the output of who to grep and look for matches of kc498

7. Searching for text patterns with regular expressions  A regular expression describes a pattern in a set of strings.  As in the previous examples, letters and numbers are regular expressions of themselves.  Use the escape character \ to precede any special meta- character. (Also has other uses when used with different characters.)  Regular expressions can be concatenated  Use parentheses to override precedence and group.

8. Repetition and Placement Operators OperatorMatchesExample.Any single character except newline.an matches "ran" and "can" in the phrase "bran muffins can be tasty" ^Beginning of line^A matches any line starting with “A” $End of input or line h$ matches "h" in "teach" but not in "teacher” grep ‘^$’ searches for blank lines *The preceding character 0 or more times. um* matches "um" in “bum", "umm" in "yummy", and "u" in "huge" +The preceding character 1 or more times. um+ matches "um" in "rum" and "umm" in "yummy" but nothing in "huge" ?The preceding item is optional and will be matched at most once. st?on matches "son" in "Johnson" and "ston" in "Johnston" but nothing in "Appleton" or "tension" x|yEither x or yFF0000|0000FF matches "FF0000" in bgcolor="#FF0000" and "0000FF'" in font color="#0000FF"

9. Searching for ranges and multiple matches  {n}  Match preceding item exactly n times  {n,}  Match preceding item at least n times  {,m}  Match preceding item at most m times  {n,m}  Match preceding item between n and m times.  [ ]  match any one of the enclosed characters, as in [aeiou]. Use Hyphen "-" for a range, as in [0- 9].  [^ ]  match any one character except those enclosed in [ ], as in [^0-9]

10. More special uses of \  \b Matches a word boundary. Ex: \dog\b will match occurrences of the word “dog” (similar to –w).  \d Matches any digit, the same as [0-9]  \D Matches any non-digit, the same as [^0-9]  \w Wildcard—Matches any alphanumeric character, including underscore. Equivalent to [A-Za-z0-9_]  \s Matches any single whitespace character (space, tab, etc.)  \S Matches any single non- whitespace character  \W Matches any non-alphanumeric character  \r carriage return  \n line feed

11. Regular Expression Tester  http://www.cs.drexel.edu/~introcs/Fa09/extras/Reg Exp/RegExp_tester.html

12. References  Robbins, Arnold. UNIX In a Nutshell. 4th ed. Safari Books Online: O'Reilly, 2005. Web.  Magloire, Alain, et al. GNU Grep: Print lines matching a pattern. Free Software Foundation, Inc. 8 September 2010. Web.  Wikipedia Contributors. "Metacharacter." Wikipedia. 17 May 2010. Web. 24 Sept. 2010..  "Regular Expressions in Grep." Robelle: Solid Software for HP Servers. Web. 24 Sept. 2010..  "About Regular Expressions." Drexel University Computer Science. Web. 25 Sept. 2010..