Overview of the grep Command

1. Overview of the grep Command Alex Dukhovny CS 265 Spring 2011

2. What is grep Command • grep - "general regular expression parser“ • Search command for UNIX. • Used to search for text strings and regular expressions within one or more files. • man grep

3. Common grep Command Options grep [options] pattern [files] • -b Display the block number at the beginning of each line. • -c Display the number of matched lines. • -h Display the matched lines, but do not display the filenames. • -i Ignore case sensitivity. • -l Display the filenames, but do not display the matched lines. • -n Display the matched lines and their line numbers. • -s Silent mode. • -v Display all lines that do NOT match. • -w Match whole word. grep -c Alex my_file.htm

4. How to use grep command • Search file for a user • $ grep ad85 /etc/passwd • Search file ignoring word case • $ grep -i “ad85" /etc/passwd • Search recursively all files and directories under given directory • $ grep -r “ad85" /etc/

5. How to use grep command • Search for a specific word in file • $ grep -w “alex" $HOME/cs265.htm • Search for 2 different words in file • $ grep -w ‘alex|victoria' $HOME/cs265.htm • Count lines that matched in file • $ grep -c 'word' $HOME/cs265.htm

6. How to use grep command • Display lines that did not match a pattern • $ grep -v cs265 $HOME/cs265.htm • Number of lines that contain matched pattern • $ grep -n 'word' $HOME/cs265.htm • Display filenames that matched pattern, but not lines from the files • $ grep -l ‘word' *.htm

7. grep and Wildcards • Dot ( . ) – matches 1 character • Asterisks ( * ) – matches multiple characters • Examples: • grep b.g myfile  finds the words “big”, “bag” • grep b*k myfile  finds the word “back”, “buck”, “book”

8. grep and Regular Expressions • A "regular expression" is a pattern that describes a set of strings. • Regular expressions are used when you want to search for specific lines of text containing a particular pattern.

9. grep and Regular Expressions • ^ (Caret) = match expression at the start of a line, as in ^A. • $ (Dollar Sign) = match expression at the end of a line, as in A$. • \ (Back Slash) = turn off the special meaning of the next character, as in \^. • [ ] (Brackets) = 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. grep and Regular Expressions • . (Period) = match a single character of any value, except end of line. • * (Asterisk) = match zero or more of the preceding character or expression. • \{x,y\} = match x to y occurrences of the preceding. • \{x\} = match exactly x occurrences of the preceding. • \{x,\} = match x or more occurrences of the preceding.

11. grep and Regular Expressions • grep bob files {search files for lines with ‘bob'} • grep '^bob' files {‘bob' at the start of a line} • grep ‘bob$' files {‘bob' at the end of a line} • grep '^bob$' files {lines containing only ‘bob'} • grep '\^b' files {lines starting with '^b', "\" escapes the ^} • grep '[Bb]mug' files {search for ‘Bob' or ‘bob'} • grep 'B[oO][bB]' files {search for BOB, Bob, BOb or BoB } • grep '^$' files {search for empty lines} • grep '[0-9][0-9]' files {search for pairs of numeric digits}

12. grep and Regular Expressions Questions ?