Grep Tutorial

grep stands for Global Regular Expression Print. This command is used to search for particular string or keyword from a file and print those lines matching a pattern in the shell. It checks line by line and print those lines matching a pattern. It can be use anywhere like with files, searching for file, directories, etc.

Grep command syntax:

grep [OPTION].. Pattern [File]..

Examples

• Basic Example

    #csv1
    id,firstname,lastname,email,profession
    100,Mady,Cloris,Mady.Cloris@gmail.com,police officer
    101,Nita,Eiser,Nita.Eiser@gmail.com,worker
    102,Ada,Rosette,Ada.Rosette@gmail.com,worker
    103,Demetris,Teryn,Demetris.Teryn@gmail.com,worker
    104,Mahalia,Sperling,Mahalia.Sperling@gmail.com,firefighter
    105,Deirdre,Lemuela,Dierdre.Lemeuela@gmail.com,firefighter
    106,Cyndie,Chem,Cyndie.Chem@gmail.com,police officer
    107,Modestia,Engdah,Modestia.Engdah@gmail.com,doctor
    108,Jaime,Corabella,Jaime.Corabella@gmaio.com,police officer
    109,Gusty,Jehu,Gusty.Jehu@gmail.com,doctor
  

  Now, to search for Nita in the following file we use: Syntax: grep {keyword/pattern} {filename}

  grep Nita csv1

  Output:
  101,Nita,Eiser,Nita.Eiser@gmail.com,worker

• To ignore the upper and lower case while searching we use:

  Syntax: grep -i {keyword/pattern} {filename}

  grep -i nita csv1

  Output:
  101,Nita,Eiser,Nita.Eiser@gmail.com,worker

• To search everything except given pattern/keyword

  Syntax: grep -v {keyword/pattern} {filename}

  grep -v Nita csv1

  Output:
  id,firstname,lastname,email,profession 100,Mady,Cloris,Mady.Cloris@gmail.com,police officer 102,Ada,Rosette,Ada.Rosette@gmail.com,worker 103,Demetris,Teryn,Demetris.Teryn@gmail.com,worker 104,Mahalia,Sperling,Mahalia.Sperling@gmail.com,firefighter 105,Deirdre,Lemuela,Dierdre.Lemeuela@gmail.com,firefighter 106,Cyndie,Chem,Cyndie.Chem@gmail.com,police officer 107,Modestia,Engdah,Modestia.Engdah@gmail.com,doctor 108,Jaime,Corabella,Jaime.Corabella@gmaio.com,police officer 109,Gusty,Jehu,Gusty.Jehu@gmail.com,doctor

• To print how many times (count) given keyword is present in the file

  Syntax: grep -c {keyword/pattern} {filename}

  grep -c “police officer” csv1

  Output:
  3

• To search for exact match of given keyword in a file

  Syntax: grep -w {keyword/pattern} {filename}

  grep -w Nit csv1

  Output: {blank}

  grep -w Nita csv1

  Output:
  101,Nita,Eiser,Nita.Eiser@gmail.com,worker

• To print the line no. of matches of given keyword in a file

  Syntax: grep -n {keyword/patttern} {filename}

  grep -n Nita csv1

  Output:
  3:101,Nita,Eiser,Nita.Eiser@gmail.com,worker 12:Nitas

• To search a given keyword in multiple files

  Syntax: grep {keyword/pattern} {file1} {file2}

    #file1
    Hi
    My name is Sheldon
    Welcome to grep tutorial
  

    #file2
    Hello
    My name is Leonard
    Welcome to grep tutorial
  

  grep -n name file1 file2

  Output:
  file1:My name is Sheldon file2:My name is Leonard

• To supress file names while searching a given keyword in multiple files

  Syntax: grep -h {keyword/pattern} {file1} {file2}

  grep -h name file1 file2

  Output:
  My name is Sheldon My name is Leonard

• To search multiple keyword in a file

  Syntax: grep -e {keyword 1/ pattern 1} -e {keyword 2 / pattern 2} {filename}

  grep -w -e Nita -e Jaime csv1

  Output:
  101,Nita,Eiser,Nita.Eiser@gmail.com,worker 108,Jaime,Corabella,Jaime.Corabella@gmaio.com,police officer

• To search multiple keywords in multiple files

  Syntax: grep -e {keyword1} -e {keyword2} {file1} {file2}

  grep -n -e Sheldon -n -e Leoanrd file1 file2

  Output:
  file1:2:My name is Sheldon file2:2:My name is Leonard

• To only print filenames which matches given keyword

  Syntax: grep -l {keyword} {file1} {file2}

  grep -l -e Sheldon -e Leonard file1 file2 csv1

  Output:
  file1 file2

• To get the keyword/pattern from a file and match with another file

  Syntax: grep -f {file with pattern} {file to search}

  grep -n -f keyword.txt csv1 file1 file2

  Output:
  csv1:2:100,Mady,Cloris,Mady.Cloris@gmail.com,police officer csv1:10:108,Jaime,Corabella,Jaime.Corabella@gmaio.com,police officer file1:2:My name is Sheldon file2:2:My name is Leonard

• To print the matching line which start with given keyword

  Syntax: grep ^{keyword} {file}

  grep -n ^101 csv1

  Output:
  5:103,Demetris,Teryn,Demetris.Teryn@gmail.com,worker

• To print the matching line which ends with given keyword

  Syntax: grep {keyword}$ {file}

  grep -n doctor$ csv1

  Output:
  9:107,Modestia,Engdah,Modestia.Engdah@gmail.com,doctor 11:109,Gusty,Jehu,Gusty.Jehu@gmail.com,doctor

• Suppose we have 100 files in a directory (dirA) and we need to search a keyword in all the files

  Syntax: grep -R {keyword} dirA/

  grep -n -R -f keyword.txt .

  Output:
  ./csv1:2:100,Mady,Cloris,Mady.Cloris@gmail.com,police officer ./csv1:10:108,Jaime,Corabella,Jaime.Corabella@gmaio.com,police officer ./file1:2:My name is Sheldon ./file2:2:My name is Leonard ./keyword.txt:1:Mady ./keyword.txt:2:Jaime ./keyword.txt:3:Starla ./keyword.txt:4:Selia ./keyword.txt:5:Sheldon ./keyword.txt:6:Leonard

• We can use egrep command for the multiple keywords search

  Syntax: egrep “key1|key2|key3” file

  egrep -n “Leonard

  Sheldon

  Jaime” csv1 file1 file2

  Output:
  csv1:10:108,Jaime,Corabella,Jaime.Corabella@gmaio.com,police officer file1:2:My name is Sheldon file2:2:My name is Leonard

• If you just want to search but don’t want to print on the terminal

  Syntax: grep -q {keyword} {file}

  grep -q Sheldon file1

  Output: None

  Here, the nothing is returned as output to the terminal. So it may be confusing to the user to know if the command is executed successfully or not. To figure this out, we see the exit status. We can see the exit status using echo $? command. If the echo $? command returns 0 then the last commad was executed successfully and if it returned 1 then it was not executed successfully.

  For Example: Input: grep -q Sheldon file1 Output: None Input: echo $? Output:0

  Input: grep -q Sheldon file2 Output: None Input: echo $? Output:1

• If you wnat to supress error message

  Syntax: grep -s {keyword} {file}

  grep -qs nita csv