Capture Groups

• Capture Groups are represented in parentheses.

Refer the below websites

• Regexr.com
• Cheatsheet with different dialects

Grep

• The grep command searches for a pattern of characters in a file or multiple files.
• Syntax

grep <token> filename

• In most cases we leverage piping concept of linux in using grep
• Meta characters in grep:
  1. ^ : Beginning of line (anchor) ^ubuntu
  2. $ : ending of line (anchor) ubuntu$
  3. . : any one character
  4. • : Zero or more characters
  5. [] : Matches one in the character set
  6. [^] : Matches one not in the character set
  7. \w, \W, \b,
• Grep supports Basic Regular expressions by default and in Grep we can use Extended Regular expressions

grep 'pattern' filname(s)   => Basic Regular Expression
grep -G 'pattern' filname(s)   => Basic Regular Expression
grep -E 'pattern' filename  => Extended regular expressions
grep -F 'pattern' file => No RE meta characters

• Classes:
  • [:alnum:] alphanumeric characters
  • [:alpha:]
  • [:cntrl:]
  • [:digit:]
  • [:lower:]
  • [:punct:]
  • [:upper:]
  • [:space:]
• Lets take this as an example

northwest	nw		John Cena		34		3.5
west		we		Big Show		43		1.5
southwest	sw		Roman Reigns	28		2.5
northeast	ne		Becky Lync		26		4.5

• Using grep to match all lines with nw
• Find all the lines Which begin with n => cat sales.dat| grep '^n'
• Find all the lines that contain .5 in it =
• Download some sample from here
• We are using 1000 samples

Region,Country,Item Type,Sales Channel,Order Priority,Order Date,Order ID,Ship Date,Units Sold,Unit Price,Unit Cost,Total Revenue,Total Cost,Total Profit
Middle East and North Africa,Libya,Cosmetics,Offline,M,10/18/2014,686800706,10/31/2014,8446,437.20,263.33,3692591.20,2224085.18,1468506.02
North America,Canada,Vegetables,Online,M,11/7/2011,185941302,12/8/2011,3018,154.06,90.93,464953.08,274426.74,190526.34
Middle East and North Africa,Libya,Baby Food,Offline,C,10/31/2016,246222341,12/9/2016,1517,255.28,159.42,387259.76,241840.14,145419.62
Asia,Japan,Cereal,Offline,C,4/10/2010,161442649,5/12/2010,3322,205.70,117.11,683335.40,389039.42,294295.98
Sub-Saharan Africa,Chad,Fruits,Offline,H,8/16/2011,645713555,8/31/2011,9845,9.33,6.92,91853.85,68127.40,23726.45
Europe,Armenia,Cereal,Online,H,11/24/2014,683458888,12/28/2014,9528,205.70,117.11,1959909.60,1115824.08,844085.52
Sub-Saharan Africa,Eritrea,Cereal,Online,H,3/4/2015,679414975,4/17/2015,2844,205.70,117.11,585010.80,333060.84,251949.96
Europe,Montenegro,Clothes,Offline,M,5/17/2012,208630645,6/28/2012,7299,109.28,35.84,797634.72,261596.16,536038.56
Central America and the Caribbean,Jamaica,Vegetables,Online,H,1/29/2015,266467225,3/7/2015,2428,154.06,90.93,374057.68,220778.04,153279.64

• Match all the lines which start with vowel using extented grep

cat sales.csv | grep -E '^[AEIOU]'
cat sales.csv | egrep '^[AEIOU]'