Frequently the initial two characters on the initial line of a script are: #!.

Why Shebang? Well, simple reason, because shell needs to know which interpreter to use when executing the script.

The sha-bang (#!) at the head of a script tells your system that this file is a set of commands to be fed to the command interpreter indicated. The #! is actually a two-byte magic number, a special marker that designates a file type, or in this case an executable shell script (type man magic for more details on this fascinating topic). Immediately following the sha-bang is a path name. This is the path to the program that interprets the commands in the script, whether it be a shell, a programming language, or a utility. This command interpreter then executes the commands in the script, starting at the top (the line following the sha-bang line), and ignoring comments. - Starting Off With a Sha-Bang

The shebang line is usually ignored by the interpreter because the # character is a comment marker in many scripting languages. Even the actual script is written with a different commenting character, such as in JavaScript:

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#!/usr/bin/env node
// JavaScript stuff starts here.

Because the first line is interpreted by the shell, and the rest is passed into JavaScript interpreter, in this case, Node.

The syntax of shebang:

#! interpreter [optional-arg]

Whether there is a space between shebang character and the interpreter or not, it does not matter.

The interpreter must usually be an absolute path to a program that is not itself a script. The following are example interpreters:

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#! /bin/sh
#! /bin/bash

More examples are via head -n 1 /etc/init.d/*.

The optional‑arg should either not be included or it should be a string that is meant to be a single argument (for reasons of portability, it should not contain any whitespace). - Shebang_(Unix)

We also frequently see the following shebang:

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#!/usr/bin/env bash

That has to do with portability. Not every system install node or bash command in the same path. /usr/bin/env will search through user’s $PATH, and correctly locate the executable.

To conclude for Node, here is the format I am using:

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#! /usr/bin/env node
// Title
// =====
//
// Markdown style description starts here.
'use strict';

By using Linux date command, we can get today’s date in the following format:

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$ date +%Y-%m-%d
2013-11-14

To get yesterday’s date, we can use the --date or -d option:

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% date -d 'yesterday' +%Y-%m-%d
2013-11-13
% date -d '-1 day' +%Y-%m-%d
2013-11-13
% date -d '1 day ago' +%Y-%m-%d
2013-11-13

As the manual explains:

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DATE STRING
       The --date=STRING is a mostly free format human  readable  date  string
       such  as  "Sun, 29 Feb 2004 16:21:42 -0800" or "2004-02-29 16:21:42" or
       even "next Thursday".  A date string may contain items indicating  cal‐
       endar  date,  time of day, time zone, day of week, relative time, rela‐
       tive date, and numbers.  An empty string indicates the beginning of the
       day.   The date string format is more complex than is easily documented
       here but is fully described in the info documentation.

Just be careful when you are trying to get the date from last month.

All time zone files are located:

/usr/share/zoneinfo

Locate the timezone file name such as Asia/Hong_Kong:

Change the time zone as root:

echo 'Asia/Hong_Kong' > /etc/timezone 

Configure time zone data:

dpkg-reconfigure --frontend noninteractive tzdata

Sync clock:

ntpdate pool.ntp.org