Keywords

• • • Exclamation mark: !
• #
  • • Hello Name with interpolation
    • Interpolation
• $?
  • • Execute external program (backtick)
• %
  • • Escaping - Alternative quote as delimiters
• %r
  • • Alternate delimiter matching slashes
• &
  • • Ampersand: &
• +
  • • Add numbers - concatenate strings
• ..
  • • Range using dots
• ...
  • • Range using dots
• /
  • • Join / concatenate file system path
• 0_i64
  • • Create Array with nil
• <
  • • Comparison Operators
• <<
  • • Array push, append, <<
• <<-
  • • Here documents
• <=
  • • Comparison Operators
• <=>
  • • Spaceship operator
• ==
  • • Comparison Operators
• >
  • • Comparison Operators
• >=
  • • Comparison Operators
• ?
  • • Type or Nil
    • Question mark: ?
• ?:
  • • Ternary operator and or to set default value
• @
  • • Class with attributes
• `
  • • Execute external program (backtick)
• abort
  • • Abort
• abs
  • • Methods of Int32
    • Methods of Float64
• append
  • • Array push, append, <<
    • Append to file
• ARGV
  • • Command line arguments - ARGV
    • ARGV
• Array
  • • Compound Types - typeof
• base64
  • • Random as a class
• begin
  • • Catch exception - begin, rescue
• blank?
  • • Is the string empty or blank?
• Bool
  • • Types - typeof
• break
  • • loop
    • Range and loop controls
• case
  • • case / when
• cd
  • • Temporary directory
• Channel
  • • Send and receive
• chars
  • • Split characters
• class
  • • Empty Class definition
• class_property
  • • Singleton using class properties
    • Singleton using class properties with default values
• clear
  • • Clear - empty a hash
• compact
  • • Remove nil elements
• continue
  • • loop controls (next, break)
    • Range and loop controls
• days
  • • Add timespan
• default
  • • Function parameter default value
• delete
  • • Delete element from array by value
    • Delete - remove an element from a hash
• delete_at
  • • Delete element from array by location
• dig
  • • Dig a hash
• dig?
  • • Dig a hash
• Digest::MD5.hexdigest
  • • Gravatar
• Dir
  • • List directory content
    • List directory tree
• each
  • • Array iterate over (each, each_with_index)
    • Count words
• each_char
  • • Iterate over characters of a string
• each_key
  • • Hash intro
• each_line
  • • Read file line-by-line
• each_with_index
  • • Array iterate over (each, each_with_index)
• else
  • • if statement
• elsif
  • • elsif
• empty?
  • • Is the string empty or blank?
    • Create empty hash
    • Size of file?
• end
  • • if statement
• ends_with
  • • String ends with
• enum
  • • Enums
• ENV
  • • Environment variables
• eval
  • • Crystal one-liners
• even
  • • Methods of Int32
• exists?
  • • Does file exist?
• exit
  • • Early exit
    • Execute external program (Process)
• exit_code
  • • Execute external program (Process)
• exit_status
  • • Execute external program (Process)
• expand
  • • Expand Path
• file_utils
  • • Temporary directory
• FileUtils
  • • Temporary directory
• filter
  • • Select (filter, grep)
    • Reject (negative filter, grep)
• first
  • • First element of the array
• first?
  • • First element of the array
• Float64
  • • Types - typeof
• from_json
  • • Multi Counter JSON
    • Serialize Crystal-lang class to/from JSON from_json to_json
    • JSON to NamedTuple
    • JSON to Array
• from_yaml
  • • Multi Counter YAML
• gcd
  • • Methods of Int32
• GET
  • • Kemal GET parameters
• gets
  • • Read from STDIN
• getter
  • • Class with getters and setter (property)
    • Class with declared getter and default value
    • Class with declared getter
• glob
  • • List directory tree
• grep
  • • Select (filter, grep)
    • Reject (negative filter, grep)
• gsub
  • • Substitute
• has_key
  • • Hash intro
• has_value
  • • Hash intro
• Hash
  • • Compound Types - typeof
• hex
  • • Random as a class
• hours
  • • Add timespan
• http/client
  • • HTTP Client example
• HTTP::Client
  • • HTTP Client example
• if
  • • if statement
    • Suffix if
• include
  • • Struct from JSON - manual parsing
• includes?
  • • String includes another string
    • Does array include a value
• index
  • • Locate substring (index, rindex)
• Infinity
  • • Divide by zero is Infinity
• initialize
  • • Initialize immutable struct
    • Struct both from JSON and initialize
    • Class with attributes
• insert
  • • Insert element into array at location
• Int32
  • • Types - typeof
• json
  • • Multi Counter JSON
    • JSON (to_json, parse)
• JSON
  • • JSON to NamedTuple
    • JSON to Array
• JSON::PullParser
  • • Struct from JSON - manual parsing
• JSON::Serializable
  • • Struct from JSON
    • Serialize Crystal-lang class to/from JSON from_json to_json
• keys
  • • Hash intro
• last_id
  • • SQLite last_id last_insert_id
• last_insert_id
  • • SQLite last_id last_insert_id
• length
  • • Length or size of a string
• loop
  • • loop
• map
  • • Transform with map
    • Transform with map
• Math
  • • Math - PI
• merge
  • • Merge hashes
    • Merge hashes
• microseconds
  • • Elapsed time
• minutes
  • • Add timespan
• modification_time
  • • Last Modified date of file?
• monotonic
  • • Elapsed time
• NamedTuple
  • • Compound Types - typeof
    • JSON to NamedTuple
    • Reading a JSON file
• next
  • • loop controls (next, break)
    • Range and loop controls
• next_bool
  • • Random as a class
• next_float
  • • Random as a class
• next_int
  • • Random as a class
• Nil
  • • Type or Nil
• nil
  • • Check if variable is nil?
• nil?
  • • Check if variable is nil?
• option_parser
  • • Command line Option Parser (argparse, GetOpts)
• OptionParser
  • • Command line Option Parser (argparse, GetOpts)
• p
  • • Debugging print p!
    • Types - typeof
• parse
  • • JSON (to_json, parse)
• Path
  • • Join / concatenate file system path
    • Join / concatenate file system path
• permutations
  • • Permutations
• PI
  • • Math - PI
• POST
  • • Kemal POST parameters
• print
  • • Hello World (print)
• printf
  • • printf
• Proc
  • • Proc
• PROGRAM_NAME
  • • Program name
• property
  • • Class with getters and setter (property)
    • Class with property with default value
• push
  • • Array push, append, <<
• puts
  • • Hello World (puts)
• rand
  • • rand
• Range
  • • Range using a class
• read
  • • Read from file (slurp)
• receive
  • • Send and receive
• reject
  • • Reject (negative filter, grep)
    • Reject (negative filter, grep)
    • Reject - remove an element from a hash
    • Reject - remove an element from a hash
• rescue
  • • Catch exception - begin, rescue
• return
  • • Function return value
• reverse
  • • Reverse a string
• rindex
  • • Locate substring (index, rindex)
• rm_rf
  • • Temporary directory
• round
  • • Methods of Int32
    • Methods of Float64
• sample
  • • Sample from array
• seconds
  • • Elapsed time
    • Add timespan
• seed
  • • Random - seed
• select
  • • Select (filter, grep)
    • Select (filter, grep)
    • Select - keep certain key-value pairs
    • Select - keep certain key-value pairs
• send
  • • Send and receive
• shards
  • • Crystal Shards (3rd party libraries)
• shift
  • • Arrays shift - remove first element
• shuffle
  • • Shuffle array
• size
  • • Length or size of a string
    • Is the string empty or blank?
    • Hash intro
    • Size of file?
• sleep
  • • Sleep
    • Elapsed time
• slurp
  • • Read from file (slurp)
• spawn
  • • Send and receive
• split
  • • Split String
    • Split characters
• SQLite
  • • Try SQLite
    • Multi-counter with SQLite
• starts_with
  • • String starts with
• STDERR
  • • STDERR, STDOUT
• STDOUT
  • • STDERR, STDOUT
• step
  • • Range with step
• String
  • • Types - typeof
• struct
  • • Empty struct
• sub
  • • Replace part of a string (substitute)
    • Substitute
• success?
  • • Execute external program (backtick)
• switch
  • • case / when
• system
  • • Execute external program (system)
• tempdir
  • • Temporary directory
• tempname
  • • Temporary directory
• Time
  • • Dates and Time
• Time::Span
  • • Dates and Time
• to_a
  • • Range to Array
• to_f
  • • Type conversion from string to float, to int
    • Converting string to integer or float
• to_f?
  • • Converting string to integer or float
• to_i
  • • Type conversion from string to float, to int
    • Converting string to integer or float
• to_i?
  • • Converting string to integer or float
• to_json
  • • Multi Counter JSON
    • Serialize Crystal-lang class to/from JSON from_json to_json
    • JSON (to_json, parse)
• to_s
  • • Stringification to_s
    • Timestamp formatting
• to_yaml
  • • Multi Counter YAML
• total_microseconds
  • • Elapsed time
• total_milliseconds
  • • Elapsed time
• total_seconds
  • • Elapsed time
• tr
  • • String Transliteration
• Tuple
  • • Compound Types - typeof
• typeof
  • • Types - typeof
    • Compound Types - typeof
• uniq
  • • Arrays uniq elements
    • Arrays uniq elements
• unless
  • • unless statement
    • Suffix unless
• until
  • • until
• URI
  • • Parse URL (URI)
• when
  • • case / when
• while
  • • while
• write
  • • Write to file
• yaml
  • • Multi Counter YAML
• YAML
  • • Parse YAML
• ~
  • • Expand Path