$ egrep -i by:(.*)$ test.txt By: Tobias Highfill
What is grep? In UNIX systems grep is a command line tool to search files using regular expressions. What are regular expressions? Regular expressions are strings used for pattern matching. What are strings? How did you get into this class?
Regex crash course ● Most characters stand for themselves ● Metacharacters represent other characters and can only be represented by escaping ● Sections of text can be captured using parenthesis ● Characters like “*” “+” and “?” allow segments to repeat
Example regex by:(.*)$ ● Normal characters ● Capturing group ● Repeat character (0 or more times) ● Metacharacters ○ “.” matches any character ○ “$” matches the end of the line
Different grep flavors ● grep ○ vanilla, normal ● egrep ○ extended grep with additional character support ● fgrep ○ “fast grep,” doesn’t use regex so it’s way faster
How to use grep grep commands have three sections: 1. Options* 2. Pattern 3. Files* *optional grep [OPTIONS]... PATTERN [FILES]...
Wait files are optional? ● If no files are provided grep will read the standard input and analyze that. ● This makes grep amazing for piping. ● Don’t want to read the entire man page for a program? Grep for keywords! man gcc | fgrep -in target
Common grep options ● -c, --count ● -e regexp , --regexp= regexp ● -f file , --file= file ● -i, --ignore-case ● -h, --no-filename ● -l, --files-with-matches ● -n, --line-number ● -s, --no-messages ● -v, --invert-match ● -x, --line-regexp
When am I ever gonna use this? ● Searching large files for pertinent information ● Searching your file system for a particular pattern ● Great for piping! ● Finding the source code for your regex golf solver Source: xkcd.com/1313
Demonstration I will now demonstrate grep using cygwin
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