grep

Select lines from file matching patterns.

grep PATTERN FILE

PATTERN is a regular expression.

How:

• Get list of students studying geography:

  grep 'Geo' ~/grep/namelist

  Tom     2C      Geo, Phy, Eng, Chin
  David   3E      Geo, Phy, Eng, Chin
  Charles 2E      Geo, Chem, Eng, Chin, Math

• Get list of students in class 6A:

  grep '6A' ~/grep/namelist

  John    6A      Computer, Math, Eng, Chin, PE
  Peter   6A      Math, Eng, Chin, PE
  Joseph  6A      Computer, Math, Eng, Chin, PE

• Get list of students in Form 2:

  grep '2[A-F]' ~/grep/namelist

  Mary    2B      Math, Bio, Eng, Chin
  Tom     2C      Geo, Phy, Eng, Chin
  Charles 2E      Geo, Chem, Eng, Chin, Math

(for details of regular expression, see manpage on regex - man 7 regex)