Mysql Question posted in
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Mysql – Understanding the meaning of the following method in linux/bash

DB_USER = 'db_user'
DB_PASS = 'db_pass'
DB_HOST = 'db_host'
DB = 'db'

function dbConnection() {
 echo "$1" | mysql -u${DB_USER} -p${DB_PASS} -h${DB_HOST} ${DB} -N
}

Request you to ignore the actual values of the db variables.
I wanted to understand the meaning of the above method. I have the following doubts:

  1. What is echo "$1" doing here?
  2. Why are we using the pipe operator?
  3. And what is the relation between the echo command and the mysql command?
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2

Answers


  1. 0

    mysql is able to read queries from stdin and | connects the stdout of the left-hand side command to the stdin of the right-hand side command. So echo "$1" will write a query (the first argument passed to dbConnection) to stdout which will be then read by the mysql command from its stdin.

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  2. 0

    Try passing it some valid SQL.

    dbConnection "SELECT 1+2;"

    The string passed becomes the argument passed in.

    echo "$1"

    becomes (effectively)

    echo "SELECT 1+2;"

    which the pipe then connects to mysql`’s stdin – it becomes the input to the program.

    It’s the script to execute.

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