oilbeater

ref = 'https://docs.python.org/3/library/functools.html'

@lru_cache(maxsize=None)
def fib(n):
    if n < 2:
        return n
    return fib(n-1) + fib(n-2)

oilbeater

// use shell command
import subprocess
output = subprocess.check_output('dir', shell=True)
print(output)

oilbeater

#Batch move
ls | head -n 50 | xargs -i mv {} mvdir/

#Batch files replace
sed -i "s/older/newser/g" `grep -li older *`

oilbeater

#!/bin/bash -x

# To count row number of each table in a schema
# Example: echo 127.0.0.1 root rootpassword rootdatabase | ./count_database.sh 2>/dev/null

while read host username password schema; 
    do
        mysql -h$host -u$username -p$password -Ne "select table_name from information_schema.tables where table_schema='${schema}'"|
        while read table;
            do

oilbeater

* Change the column property
    ALTER TABLE table_name MODIFY COLUMN column_name VARCHAR(50);

* Create table from exist table
    CREATE TABLE table_name LIKE exist_table;  //empty table with same structure
    CREATE TABLE table_name AS SELECT * FROM exist_table;  //copy the whole table

* Estimate rough row number of a database
    SELECT TABLE_NAME,TABLE_ROWS FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_SCHEMA=table_schema; // this is only an estimate,not the exact one!!!!!