Intro handson

Introduction to NGS hands-on workshop

( This document is a work in progress )

This document includes talk points and workshop tasks for the "Introduction to NGS hands-on workshop".

Why NGS

• Covers the modern ops domain-specific niche.
  • bash is not modern
  • python, ruby, go are not ops domain-specific

Intro to NGS

Installing NGS

TODO: installation, verification

Running and exiting NGS

NGS has several mechanisms for integration with the environment. Running and exiting NGS are the prominent ones.

• Switches: -e, -p, -pl, -pj, -pjl
  • ngs -e 'echo("Hello!")'
  • ngs -p '"Hello!"'
  • ngs -pl '[1,"aha",2]'
  • ngs -pl '0..5'
  • ngs -pj '["a", "b", "c"] * 2'
  • ngs -pjl '["a", "b", "c"] * 2'
• Exit codes - all objects are converted to exit codes using ExitCode.
  • Of a process
    • ngs -e '$(true)'; echo $?
    • ngs -e '$(false)'; echo $?
    • ngs -e '$(bash -c "exit 10")'; echo $?
    • ngs -e '$(ok: bash -c "exit 10")'; echo $?
  • Of an NGS object
    • ngs -e true; echo $?
    • ngs -e false; echo $?
    • ngs -e 10; echo $?
    • ngs -e '"abc" ~ /^a/'; echo $?
    • ngs -e '"abc" ~ /^x/'; echo $?
• die()
  • ngs -e 'die("mymessage")'; echo $?
  • ngs -e 'die("mymessage", 10)'; echo $?
• exit()
  • ngs -e 'exit()'; echo $?
  • ngs -e 'exit(10)'; echo $?
  • ngs -e 'exit("mymessage")'; echo $?
  • ngs -e 'exit("mymessage", 10)'; echo $?

Syntax basics

NGS has two syntaxes: commands syntax and expressions syntax.

The reasoning behind two syntaxes: common ops tasks include running external programs, including

• The two syntaxes and switching between them
  • Commands syntax (in a file)
    • This is the top level syntax in a file, similar to other shells
    • ls
    • ls >ls.txt
    • Switching to expressions syntax
      • Code block: { "aaa".echo() }
      • RHS of assignment: =, +=, -=, *=, /=, .=
      • Function definition: F f(x) x*10
      • Function call: echo(...) (but not func.method(...) yet)
      • Namespace declaration: ns { ... }
      • Control structures: if, while, switch, for
      • echo ${1+2}
  • Expressions syntax
    • This is the syntax in:
      • (A) command line switches
      • (B) after switch from commands syntax via one of the syntax constructs above
    • All the things that worked in commands syntax work, except for running external commands
    • Things that are exclusive to expressions syntax
      • 1 + 2
      • [1,2,3].each(echo)
    • Switching to commands syntax
      • ngs -e '$(ls)'
      • ngs -e '$(top_level:: ls)'
      • ngs -p '$(ls)'
      • ngs -pi '$(ls)' (-pi is explained in next section)
      • ngs -pi '$(ls | wc -l)'

Inspecting NGS objects

• -pi switch
  • ngs -pi Str
  • ngs -pi Str.constructors
  • ngs -pi ExitCode
• inspect()
  • ngs -e '["a", "b", "c" ].inspect().echo()'
    • data.method() and method(data) syntax
  • ngs -e '["a", "b", "c" ].inspect().each(echo)'
    • each() - one of the basic components of functional programming

A bit about data manipulation and functional programming

• What is functional programming?
• Why functional programming is good for data manipulation?
• Function definition
  • Named: ngs -p 'F f(x) x*2; f(10)'
  • Anonymous:
    • ngs -p 'f = F(x) x*2; f(10)'
    • ngs -p '(F(x) x*2)(10)'
• Basic higher order functions: each, map, filter, reject, Pred
  • ngs -e '[1,2,3].each(echo)'

Workshop - Hackernews tail

The workshop will be primarily focused on ops-specific aspects of NGS

Phase 1 - get the data

• Comments
  • # HackerNews API documentation: https://github.com/HackerNews/API
• Assignment
  • BASE_API_URL = 'https://hacker-news.firebaseio.com/v0'
• Get items (stories) list
  • newstories = ``curl -s "${BASE_API_URL}/newstories.json"``
    • Quick points about sibling commands
      • $(run syntax)
      • `run-and-capture syntax`
    • Exit codes when NGS is running external programs and related exceptions
  • Limit items number:
    • newstories = newstories.limit(10)
    • newstories .= limit(10) (same as x += 1)
• Get information about each item and display it

for i in reverse(newstories) {
	item = ``curl -s "${BASE_API_URL}/item/${i}.json"``
	# Sometimes "item" is null
	not(item) continues
	echo("-" * 80)
	echo("${Time(item.time)} [${item.by}] [${item.score}] ${item.title}")
	for k in %[url text] {
		# Display item's .url / .text if exist
		if k in item {
			echo(item[k])
		}
	}
}

Phase 2 - track state

• Accessing environment variables using ENV
• ENV.HOME / '.hn_state.json'
• try
  • try fetch(STATE_FILE)
  • Mention try EXPR catch(e:Exception) HANDLER
• fetch(filename:Str)
• store(filename:Str, data:Any)
• filter()

Phase 3 - polling

• while CONDITION EXPR
• $(sleep ...)

Phase 4 - wrap in main and parametrize

• main() and arguments matching
  • main() is not required
  • Command line arguments are matched automatically
  • Parametrize interval
  • Add once option