Programming Languages - Date / Time

Get Current Time

JavaScript

var date = new Date();

// date
date.getDate();

// month(0-11)
date.getMonth() + 1;

// year(201x)
date.getFullYear();

// get previous day
date.setDate(date.getDate() - 1);

// get epoch
new Date() - new Date(0);

Bash

Suppose today is 2020-01-01

$ date +%Y%m%d
20200101

Conversion Between Unix Time and Readable Timestamp

Convert from seconds to time string:

$ date -d @1622999905
Sun Jun  6 10:18:25 PDT 202

In ISO 8601 format:

$ date -d @1622999905 -Iseconds
2021-06-06T17:18:25+00:00

With timezone:

$ TZ=":America/Los_Angeles" date -d @1622999905
Sun 06 Jun 2021 10:18:25 AM PDT

Get Running Time

Java

long start = System.currentTimeMillis();
method();
long end = System.currentTimeMillis();

System.out.println("Time used: " + (end – start));

Create Padded Dates

$ seq -f "%02g" 1 31
01
02
03
04
05
...

C++

https://abseil.io/docs/cpp/guides/time