How to use the grep command in Linux

Introduction

The grep command enables us to apply some regex matching of patterns to the contents of a text file from the terminal with the help of the Unix pipe operator ( | ). The grep command can also be used on its own.

The pipe operator ( |) works like this, take the outputs of the first command and “pipe”, and apply the outputs as inputs to the second command in one line.

The general format using the grep command is:

grep [options] pattern [file]

1. Example usage of the grep command with the pipe operator (|)

Take for instance a file list.json:

nmurgor@nmurgor:$ cat list.json | grep Kenya
  # outputs:
  "Kenya": "KE",

The cat command displays the contents of a text file to the terminal. We take this output and “pipe” to the grep command to see if the text “Kenya” is in the contents of the list.json

2. Example usage of the grep command

nmurgor@nmurgor:$ grep Ke* list.json
  # outputs
  "Comoros": "KM",
  "Kenya": "KE",

Bonus, you can use standard regex to match patterns in the text file to increase accuracy.

The contents of the list.json file look like this:

{
  "Burundi": "BI",
  "Comoros": "KM",
  "Djibouti": "DJ",
  "Eritrea": "ER",
  "Ethiopia": "ET",
  "Kenya": "KE",
  "Madagascar": "MG",
  "Malawi": "MW",
  "Mauritius": "MU",
  "Mozambique": "MZ",
  "Rwanda": "RW",
  "Seychelles": "SC",
  "Somalia": "SO",
  "South Sudan": "SS",
  "Tanzania": "TZ",
  "Uganda": "UG"
}

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