grep Examples

grep - print lines matching a pattern

grep [OPTIONS] Pattern [File...]
grep [OPTIONS] -e Pattern -f File [File...]

-E: support extended regexp
-e <PATTERN>: Use <PATTERN> as pattern. Can be used multiple times (OR semantic)
-i: ignore case
-v: invert match 
-o: print only the matched part (output: one line per match)
-f: obtain patterns from file
-l: files with match
-w: The pattern must match whole words (surrounded by non word characters)
-L: files without match
-A <num>: Print <num> lines after matching context.
-B <num>: Print <num> lines before matching context.  
-m <num>: Stop reading a file after <num> matching lines. 
-c: suppress normal output, instead count matching lines.
--colour: highlight match

• return lines containing the string New Zealand
  grep 'New Zealand' ../data/city.sample.csv
  [Output]

• return lines containing New
  grep 'New' ../data/city.sample.csv
  [Output]

• return lines containing the word New (\b: boundary)
  grep 'New\b' ../data/city.sample.csv
  [Output]

• return lines containing the string Burg
  grep 'Burg' ../data/city.sample.csv
  [Output]

• return lines containing the string burg
  grep 'burg' ../data/city.sample.csv
  [Output]

• return lines containing the string burg (case insensitive)
  grep -i 'burg' ../data/city.sample.csv
  [Output]

• return lines containing CH or DK
  grep -e CH -e DK ../data/city.sample.csv
  [Output]

• return lines containing the specified regular expression
  grep -E '[YVR][a-z]+b(u|e)rg\b' ../data/city.sample.csv
  [Output]

• return the matches of the specified regular expression
  grep -Eo '[YVR][a-z]+b(u|e)rg\b' ../data/city.sample.csv
  [Output]

• return lines that do not contain the characters A,E,I,a,e,i
  grep -v '[AEIaei]' ../data/city.sample.csv
  [Output]

• return lines containing the string CH
  grep -n CH ../data/city.sample.csv
  [Output]

• return lines containing the string D
  grep -n D ../data/city.sample.csv
  [Output]

• return lines (with line number) containing the single character D
  grep -n '\bD\b' ../data/city.sample.csv
  [Output]

• return the number of lines, that contain the word USA
  grep -c '\bUSA\b' ../data/city.sample.csv
  [Output]

• read searchterms from file
  grep -f countries.txt ../data/city.sample.csv
  [Output]

• return consecutive uppercase words
  grep -E -o '[A-Z][a-z]+ [A-Z][a-z]+' ../data/moby-dick.txt
  [Output]

• generates a separate file for each country (these are used in the following examples)
  rm -f ../data/city-*.csv && awk -F, '{print $0 >> "../data/city-"$2".csv"}' ../data/city.sample.csv
  [Output]

• search in multiple files
  grep New ../data/city-*.csv
  [Output]

• output only filenames
  grep New ../data/city-*.csv -l
  [Output]

• omit filenames in result
  grep New ../data/city-*.csv -h
  [Output]

• print only files that did not contain pattern
  grep New ../data/city-*.csv -L
  [Output]

• add 3 lines of context (after match)
  grep 'CHAPTER' -A3 ../data/moby-dick.txt
  [Output]

• to test a complicated regex, use echo and pipe it into grep
  echo "test if a complicated pattern matches a string" | grep -E -o '(.)\1' --colour
  [Output]