BASH MySQL 输出到动态变量

Question

I'm using the following BASH mysql statement to get data from my DB.

mysql -N -u root --password=ROOT DB -h 127.0.0.1 -e "SELECT * FROM site where id like '1234'" | while read A B C D E F G H I J K L M N O P Q R S T U V W X Y Z; do
    echo $A
    echo $B
done

To get all the values for A to Z this seems a long winded way.

How can I do this better and create variables based on the read value name and results. ?

eg: create var A which contains value of $A and do this all the way upto var Z containing the value of $Z

This is only an example, the values won't be called AZ, but have proper names. Is there any way to create variable based on the true proper name and then associate the value to it ?

eg:

mysql -N -u root --password=ROOT DB -h 127.0.0.1 -e "SELECT * FROM site where id like '1234'" | while read site_id site_location site_size etc....... mysql -N -u root --password=ROOT DB -h 127.0.0.1 -e "SELECT * FROM site where id like '1234'" | while read site_id site_location site_size etc....... ; do

Thanks

Answer 1

The mysql call needs to be piped-in to the while loop this way:

while read -r site_id site_location site_size _ ; do
  echo "$site_id" "$site_location" "$site_size"
done < <(
  mysql -N -u root --password=ROOT DB -h 127.0.0.1 -e "SELECT * FROM site where id like '1234'"
)

The < <(command) redirection allows the command to execute in a sub-shell, but feed the main thread's read . So when it read -r var1 var2 ... varn < <(command) , variables are valid for the main thread.

Whereas command | read -r var command | read -r var has command to execute in the main thread and read execute in a sub-shell, and var is only valid within the sub-shell.

Getting variable names matching each column name from the table

This script reads the table description and creates a vars array containing the column names.

It reads, creates and prints each shell variable of these names using indirection.

#!/usr/bin/env bash

# Pupulate the vars array with the column names from the table
IFS=$'\n' read -r -d '' -a vars < <(
  mysql -N -u root --password=ROOT DB -h 127.0.0.1 -e 'SHOW COLUMNS FROM site' |
    cut -d ' ' -f1
)

# Output column headers
printf '%s\t' "${vars[@]}"

# read and create variables names matching column names
while read -r "${vars[@]}"; do
  for varname in "${vars[@]}"; do
    # Use ! indirection to print the value for the variable
    printf '%s\t' "${!varname}"
  done
done < <(
  mysql -N -u root --password=ROOT DB -h 127.0.0.1 -e "SELECT * FROM site where id like '1234'"
)