Using Regular Expressions in Grep

Using Regular Expressions in Grep

• 1.
  Dan Morrill Highline CommunityCollege April 02 - 2013
• 2.
   Superheroes.txt  Alinux computer  Grep (already on your linux box)
• 3.
   Grep searchesthe 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. By default, grep prints the matching lines.  In addition, two variant programs egrep and fgrep are available. Egrep is the same as grep -E. Fgrep is the same as grep -F.
• 4.
   -E –extended-regexp (interpret a pattern (using a regular expression))  -G – basic-regexp (interpret a pattern as a basic regular expression)  -i – ignore case (important, linux is case sensitive)  -n – print the line number the match was found on  -r (-R) – recursive – search all the files under a directory for the pattern  -v – invert match – show all lines that are not matching of the pattern
• 5.
   Grep isdesigned to search for data in a file or in a list (for example, when doing ps –ef |grep http)  If you want to search for a specific item in a text document you can also use grep to find what you are looking for  grep –i man superheroes.txt  Will find everything that has the word “man” in the file and push it to the screen for you to see.
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   grep –iblack superheroes.txt  You should see a list of people who have the word man in their names  grep –i cat superheroes.txt  You should see a list of people who have the word cat in their names  grep –i spider superheroes.txt  You should see a list of people who have the word spider in their names  grep -v -i 'spider' heroes.txt  You should see a list of people without the word spider in their names
• 7.
   . (period)– match any single character  ^ - match the empty string at the top of the line  $ - match the empty string at the bottom of the line  A – match an uppercase A  a – match a lowercase a  d – match a digit (number)  D – match any non-number character (a-zA-Z)  [A-E] – match any upper case A through E (A, B, C, D, E)  [^A-E] – match any upper case character but A through E
• 8.
   X? –match no or one occurance of the captial letter X  X* - match zero or more captial x’s  X+ - match one or more captial x’s  (abc|def)+ Match a sequence of at least one abc and def, abc and def would both match
• 9.
   grep –E‘^Bat’ superheroes.txt  Matches names that start with Bat (note the cap)  What would I use to make it not case sensitive?  grep -E '^(bat|Bat|cat|Cat)‘ superheroes.txt  Matches all bat, Bat, cat, Cat in the file  grep –i –E ‘^(bat|cat)’ superheroes.txt  Matches all bat and cat regardless of case (similar to the second example without so much typing)  grep -i -E '[^b]at' superheroes.txt  Excludes all lowercase b followed by at