As developers, we often have to create command-line applications, which expose APIs, workflows, or data processing functionality in a way that is accessible to scripts and non-developers. Although a simple command-line application can be created by only using Array[String], such applications lack features that users take for granted, including flexible subcommands, options, arguments, validations and documentation pages. In this presentation, Jorge Vásquez will show you how to easily build beautiful command-line applications that your users will love. Using ZIO CLI, your command-line applications will support all types of command-line parameters, perform both Pure and Impure validation, generate beautiful short and long documentation pages, and support auto-correction plus auto-completion. Discover how you can have fun creating beautiful command-line apps that delight your users!

1. Behold! The Happy Path To
Captivate Your Users With
Stunning CLI Apps!
Functional Scala
December 2022

2. Jorge Vásquez
Scala Developer/ZIO Trainer
@Scalac

3. Scalac ZIO Trainings
If your team is interested in our ZIO
trainings:

4. Scalac ZIO Trainings
If your team is interested in our ZIO
trainings:
✓ Visit https://scalac.io/services/
training/

5. Scalac ZIO Trainings
If your team is interested in our ZIO
trainings:
✓ Visit https://scalac.io/services/
training/
✓ Or, if you are onsite at the
conference you can visit our
booth!

6. Why CLI Apps?

7. Why CLI Apps?

8. Why CLI Apps?
✓ CLI Apps make your work scriptable/testable/usable by non-
devs

9. Why CLI Apps?
✓ CLI Apps make your work scriptable/testable/usable by non-
devs
✓Around API

10. Why CLI Apps?
✓ CLI Apps make your work scriptable/testable/usable by non-
devs
✓Around API
✓Around data processing task

11. Why CLI Apps?
✓ CLI Apps make your work scriptable/testable/usable by non-
devs
✓Around API
✓Around data processing task
✓Others

12. Why CLI Apps?
✓ CLI Apps make your work scriptable/testable/usable by non-
devs
✓Around API
✓Around data processing task
✓Others
✓ Examples:

13. Why CLI Apps?
✓ CLI Apps make your work scriptable/testable/usable by non-
devs
✓Around API
✓Around data processing task
✓Others
✓ Examples:
✓AWS CLI

14. Why CLI Apps?
✓ CLI Apps make your work scriptable/testable/usable by non-
devs
✓Around API
✓Around data processing task
✓Others
✓ Examples:
✓AWS CLI
✓Git

15. Problem: Implementing
Production-Grade CLI Apps

18. Implementing Production-Grade CLI
Apps
There are several things we need to handle!

19. Implementing Production-Grade CLI
Apps
There are several things we need to handle!
✓ Command-line parameters

20. Implementing Production-Grade CLI
Apps
There are several things we need to handle!
✓ Command-line parameters
✓ Inputs validation

21. Implementing Production-Grade CLI
Apps
There are several things we need to handle!
✓ Command-line parameters
✓ Inputs validation
✓ Documentation

22. Handling Parameters

23. Handling Parameters
There are several types of Command-line Parameters

24. Handling Parameters
There are several types of Command-line Parameters
✓ Options: Named parameters

25. Handling Parameters
There are several types of Command-line Parameters
✓ Options: Named parameters
✓ Arguments: Unnamed parameters

26. Handling Parameters
There are several types of Command-line Parameters
✓ Options: Named parameters
✓ Arguments: Unnamed parameters
✓ Subcommands

27. Handling Options
$ git commit –-message "My first commit"

28. Options should be Order-insensitive!
# This command...
$ git commit –-message "My first commit" --author "Jorge Vasquez"
# Should be the same as...
$ git commit --author "Jorge Vasquez" –-message "My first commit"

29. Options should be Order-insensitive!
# This command...
$ git commit –-message "My first commit" --author "Jorge Vasquez"
# Should be the same as...
$ git commit --author "Jorge Vasquez" –-message "My first commit"

30. Options should be Order-insensitive!
# This command...
$ git commit –-message "My first commit" --author "Jorge Vasquez"
# Should be the same as...
$ git commit --author "Jorge Vasquez" –-message "My first commit"

31. We need to handle Flags!
$ git commit –-message "My first commit" --verbose

32. We need to handle Variations in
Options!
# This command...
$ git commit –-message "My first commit"
# Should be the same as...
$ git commit –-message="My first commit"
# And the same as...
$ git commit –m "My first commit"

33. We need to handle Variations in
Options!
# This command...
$ git commit –-message "My first commit"
# Should be the same as...
$ git commit –-message="My first commit"
# And the same as...
$ git commit –m "My first commit"

34. We need to handle Variations in
Options!
# This command...
$ git commit –-message "My first commit"
# Should be the same as...
$ git commit –-message="My first commit"
# And the same as...
$ git commit –m "My first commit"

35. We need to handle Variations in
Options!
# This command...
$ git commit –-message "My first commit"
# Should be the same as...
$ git commit –-message="My first commit"
# And the same as...
$ git commit –m "My first commit"

36. We need to handle Variations in
Options!
# This command...
$ git commit -v –m "My first commit"
# Should be the same as...
$ git commit -vm "My first commit"

37. We need to handle Variations in
Options!
# This command...
$ git commit -v –m "My first commit"
# Should be the same as...
$ git commit -vm "My first commit"

38. We need to handle Variations in
Options!
# This command...
$ git commit -v –m "My first commit"
# Should be the same as...
$ git commit -vm "My first commit"

39. Handling Arguments
$ cat foo.txt

40. Arguments are Order-sensitive!
# This command...
$ cp foo1.txt foo2.txt
# Is NOT the same as...
$ cp foo2.txt foo1.txt

41. Arguments are Order-sensitive!
# This command...
$ cp foo1.txt foo2.txt
# Is NOT the same as...
$ cp foo2.txt foo1.txt

42. Arguments are Order-sensitive!
# This command...
$ cp foo1.txt foo2.txt
# Is NOT the same as...
$ cp foo2.txt foo1.txt

43. We need to handle Varargs!
$ cat foo1.txt foo2.txt foo3.txt

44. Handling Subcommands
$ git clone https://github.com/zio/zio-cli.git
$ git add .
$ git commit –-message "My first commit"

45. Handling Subcommands
$ git clone https://github.com/zio/zio-cli.git
$ git add .
$ git commit –-message "My first commit"

46. Handling Subcommands
$ git clone https://github.com/zio/zio-cli.git
$ git add .
$ git commit –-message "My first commit"

47. Handling Subcommands
$ git clone https://github.com/zio/zio-cli.git
$ git add .
$ git commit –-message "My first commit"

48. Inputs Validation

49. Inputs Validation

50. Inputs Validation
✓ We need to validate inputs the user provides as options/
arguments

51. Inputs Validation
✓ We need to validate inputs the user provides as options/
arguments
✓ Two types of validation

52. Inputs Validation
✓ We need to validate inputs the user provides as options/
arguments
✓ Two types of validation
✓Pure

53. Inputs Validation
✓ We need to validate inputs the user provides as options/
arguments
✓ Two types of validation
✓Pure
✓Impure

54. Pure Validation
We need to validate whether an option/argument is a:

55. Pure Validation
We need to validate whether an option/argument is a:
✓ String

56. Pure Validation
We need to validate whether an option/argument is a:
✓ String
✓ Integer

57. Pure Validation
We need to validate whether an option/argument is a:
✓ String
✓ Integer
✓ Datetime

58. Pure Validation
We need to validate whether an option/argument is a:
✓ String
✓ Integer
✓ Datetime
✓ Other data type

59. Pure Validation
$ tail -n xyz foo.txt
# tail: illegal offset -- xyz

60. Pure Validation
$ tail -n xyz foo.txt
# tail: illegal offset -- xyz

61. Pure Validation
$ tail -n xyz foo.txt
# tail: illegal offset -- xyz

62. Impure Validation
We need to verify a connection between an option/
argument and the Real World

63. Impure Validation
We need to verify a connection between an option/
argument and the Real World
✓ Does the given file actually exist?

64. Impure Validation
We need to verify a connection between an option/
argument and the Real World
✓ Does the given file actually exist?
✓ Is the given URL valid?

65. Impure Validation
$ tail -n 500 foo.txt
# tail: foo.txt: No such file or directory

66. Impure Validation
$ tail -n 500 foo.txt
# tail: foo.txt: No such file or directory

67. Impure Validation
$ tail -n 500 foo.txt
# tail: foo.txt: No such file or directory

68. Documentation

70. Documentation

71. Documentation
✓ We need basically two types of documentation:

72. Documentation
✓ We need basically two types of documentation:
✓Synopsis

73. Documentation
✓ We need basically two types of documentation:
✓Synopsis
✓Rich documentation

74. Documentation
✓ We need basically two types of documentation:
✓Synopsis
✓Rich documentation
✓ We have to consider docs for subcommands as well!

76. Wouldn't it be dreamy if we had a
ZIO Library that handles all of this
stuff for us, so we can focus on
our Business Logic?

77. Presenting ZIO CLI!

78. What is ZIO CLI?

79. What is ZIO CLI?
✓ It's a library that allows you to rapidly build Powerful
Command-line Applications powered by ZIO

80. What is ZIO CLI?
✓ It's a library that allows you to rapidly build Powerful
Command-line Applications powered by ZIO
✓ https://github.com/zio/zio-cli

81. ZIO CLI Walkthrough

82. Sample app: CSV
Utils

83. Sample app: CSV
Utils
✓ The following subcommands should be
supported:

84. Sample app: CSV
Utils
✓ The following subcommands should be
supported:
✓ Rename a column

85. Sample app: CSV
Utils
✓ The following subcommands should be
supported:
✓ Rename a column
✓ Delete a column

86. Sample app: CSV
Utils
✓ The following subcommands should be
supported:
✓ Rename a column
✓ Delete a column
✓ Move a column to a different position

87. Sample app: CSV
Utils
✓ The following subcommands should be
supported:
✓ Rename a column
✓ Delete a column
✓ Move a column to a different position
✓ Change the separator string

88. Sample app: CSV
Utils
✓ The following subcommands should be
supported:
✓ Rename a column
✓ Delete a column
✓ Move a column to a different position
✓ Change the separator string
✓ Replicate the given CSV file into several
others with the given separators

89. Sample app: CSV
Utils
✓ The following subcommands should be
supported:
✓ Rename a column
✓ Delete a column
✓ Move a column to a different position
✓ Change the separator string
✓ Replicate the given CSV file into several
others with the given separators
✓ Convert to JSON, allowing pretty
printing

90. Create the CLI
application entrypoint

91. Create the CLI application entrypoint
import zio.cli._
object CsvUtil extends ZIOCliDefault {
val cliApp = ??? // We need to implement this
}

92. Create the CLI application entrypoint
import zio.cli._
object CsvUtil extends ZIOCliDefault {
val cliApp = ??? // We need to implement this
}

93. Create the CLI application entrypoint
import zio.cli._
object CsvUtil extends ZIOCliDefault {
val cliApp = ??? // We need to implement this
}

94. Create the CLI application entrypoint
import zio.cli._
object CsvUtil extends ZIOCliDefault {
val cliApp = ??? // We need to implement this
}

95. Define a Pure Data-
Structure that models
inputs to all possible
Subcommands

96. Define a Pure Data-Structure that
models inputs to all possible
Subcommands
sealed trait Subcommand
object Subcommand {
final case class RenameColumn(column: String, newName: String, separator: String, inputCsv: Path) extends Subcommand
final case class DeleteColumn(column: String, separator: String, inputCsv: Path) extends Subcommand
final case class MoveColumn(column: String, newIndex: BigInt, separator: String, inputCsv: Path) extends Subcommand
final case class ChangeSeparator(oldSeparator: String, newSeparator: String, inputCsv: Path) extends Subcommand
final case class Replicate(newSeparators: ::[String], separator: String, inputCsv: Path) extends Subcommand
final case class ToJson(pretty: Boolean, separator: String, inputCsv: Path, outputJson: Path) extends Subcommand
}

97. Define a Pure Data-Structure that
models inputs to all possible
Subcommands
sealed trait Subcommand
object Subcommand {
final case class RenameColumn(column: String, newName: String, separator: String, inputCsv: Path) extends Subcommand
final case class DeleteColumn(column: String, separator: String, inputCsv: Path) extends Subcommand
final case class MoveColumn(column: String, newIndex: BigInt, separator: String, inputCsv: Path) extends Subcommand
final case class ChangeSeparator(oldSeparator: String, newSeparator: String, inputCsv: Path) extends Subcommand
final case class Replicate(newSeparators: ::[String], separator: String, inputCsv: Path) extends Subcommand
final case class ToJson(pretty: Boolean, separator: String, inputCsv: Path, outputJson: Path) extends Subcommand
}

98. Define a Pure Data-Structure that
models inputs to all possible
Subcommands
sealed trait Subcommand
object Subcommand {
final case class RenameColumn(column: String, newName: String, separator: String, inputCsv: Path) extends Subcommand
final case class DeleteColumn(column: String, separator: String, inputCsv: Path) extends Subcommand
final case class MoveColumn(column: String, newIndex: BigInt, separator: String, inputCsv: Path) extends Subcommand
final case class ChangeSeparator(oldSeparator: String, newSeparator: String, inputCsv: Path) extends Subcommand
final case class Replicate(newSeparators: ::[String], separator: String, inputCsv: Path) extends Subcommand
final case class ToJson(pretty: Boolean, separator: String, inputCsv: Path, outputJson: Path) extends Subcommand
}

99. Define a Pure Data-Structure that
models inputs to all possible
Subcommands
sealed trait Subcommand
object Subcommand {
final case class RenameColumn(column: String, newName: String, separator: String, inputCsv: Path) extends Subcommand
final case class DeleteColumn(column: String, separator: String, inputCsv: Path) extends Subcommand
final case class MoveColumn(column: String, newIndex: BigInt, separator: String, inputCsv: Path) extends Subcommand
final case class ChangeSeparator(oldSeparator: String, newSeparator: String, inputCsv: Path) extends Subcommand
final case class Replicate(newSeparators: ::[String], separator: String, inputCsv: Path) extends Subcommand
final case class ToJson(pretty: Boolean, separator: String, inputCsv: Path, outputJson: Path) extends Subcommand
}

100. Define a Pure Data-Structure that
models inputs to all possible
Subcommands
sealed trait Subcommand
object Subcommand {
final case class RenameColumn(column: String, newName: String, separator: String, inputCsv: Path) extends Subcommand
final case class DeleteColumn(column: String, separator: String, inputCsv: Path) extends Subcommand
final case class MoveColumn(column: String, newIndex: BigInt, separator: String, inputCsv: Path) extends Subcommand
final case class ChangeSeparator(oldSeparator: String, newSeparator: String, inputCsv: Path) extends Subcommand
final case class Replicate(newSeparators: ::[String], separator: String, inputCsv: Path) extends Subcommand
final case class ToJson(pretty: Boolean, separator: String, inputCsv: Path, outputJson: Path) extends Subcommand
}

101. Define a Pure Data-Structure that
models inputs to all possible
Subcommands
sealed trait Subcommand
object Subcommand {
final case class RenameColumn(column: String, newName: String, separator: String, inputCsv: Path) extends Subcommand
final case class DeleteColumn(column: String, separator: String, inputCsv: Path) extends Subcommand
final case class MoveColumn(column: String, newIndex: BigInt, separator: String, inputCsv: Path) extends Subcommand
final case class ChangeSeparator(oldSeparator: String, newSeparator: String, inputCsv: Path) extends Subcommand
final case class Replicate(newSeparators: ::[String], separator: String, inputCsv: Path) extends Subcommand
final case class ToJson(pretty: Boolean, separator: String, inputCsv: Path, outputJson: Path) extends Subcommand
}

102. Define a Pure Data-Structure that
models inputs to all possible
Subcommands
sealed trait Subcommand
object Subcommand {
final case class RenameColumn(column: String, newName: String, separator: String, inputCsv: Path) extends Subcommand
final case class DeleteColumn(column: String, separator: String, inputCsv: Path) extends Subcommand
final case class MoveColumn(column: String, newIndex: BigInt, separator: String, inputCsv: Path) extends Subcommand
final case class ChangeSeparator(oldSeparator: String, newSeparator: String, inputCsv: Path) extends Subcommand
final case class Replicate(newSeparators: ::[String], separator: String, inputCsv: Path) extends Subcommand
final case class ToJson(pretty: Boolean, separator: String, inputCsv: Path, outputJson: Path) extends Subcommand
}

103. Define a Pure Data-Structure that
models inputs to all possible
Subcommands
sealed trait Subcommand
object Subcommand {
final case class RenameColumn(column: String, newName: String, separator: String, inputCsv: Path) extends Subcommand
final case class DeleteColumn(column: String, separator: String, inputCsv: Path) extends Subcommand
final case class MoveColumn(column: String, newIndex: BigInt, separator: String, inputCsv: Path) extends Subcommand
final case class ChangeSeparator(oldSeparator: String, newSeparator: String, inputCsv: Path) extends Subcommand
final case class Replicate(newSeparators: ::[String], separator: String, inputCsv: Path) extends Subcommand
final case class ToJson(pretty: Boolean, separator: String, inputCsv: Path, outputJson: Path) extends Subcommand
}

104. Define a Pure Data-Structure that
models inputs to all possible
Subcommands
// Factor commonalities out (Functional Design in action!
!
)
final case class Subcommand(separator: String, inputCsv: Path, info: Subcommand.Info)
object Subcommand {
sealed trait Info
object Info {
final case class RenameColumn(column: String, newName: String) extends Info
final case class DeleteColumn(column: String) extends Info
final case class MoveColumn(column: String, newIndex: BigInt) extends Info
final case class ChangeSeparator(newSeparator: String) extends Info
final case class Replicate(newSeparators: ::[String]) extends Info
final case class ToJson(pretty: Boolean, outputJson: Path) extends Info
}
}

105. Define a Pure Data-Structure that
models inputs to all possible
Subcommands
// Factor commonalities out (Functional Design in action!
!
)
final case class Subcommand(separator: String, inputCsv: Path, info: Subcommand.Info)
object Subcommand {
sealed trait Info
object Info {
final case class RenameColumn(column: String, newName: String) extends Info
final case class DeleteColumn(column: String) extends Info
final case class MoveColumn(column: String, newIndex: BigInt) extends Info
final case class ChangeSeparator(newSeparator: String) extends Info
final case class Replicate(newSeparators: ::[String]) extends Info
final case class ToJson(pretty: Boolean, outputJson: Path) extends Info
}
}

106. Define a Pure Data-Structure that
models inputs to all possible
Subcommands
// Factor commonalities out (Functional Design in action!
!
)
final case class Subcommand(separator: String, inputCsv: Path, info: Subcommand.Info)
object Subcommand {
sealed trait Info
object Info {
final case class RenameColumn(column: String, newName: String) extends Info
final case class DeleteColumn(column: String) extends Info
final case class MoveColumn(column: String, newIndex: BigInt) extends Info
final case class ChangeSeparator(newSeparator: String) extends Info
final case class Replicate(newSeparators: ::[String]) extends Info
final case class ToJson(pretty: Boolean, outputJson: Path) extends Info
}
}

107. Define a Pure Data-Structure that
models inputs to all possible
Subcommands
// Factor commonalities out (Functional Design in action!
!
)
final case class Subcommand(separator: String, inputCsv: Path, info: Subcommand.Info)
object Subcommand {
sealed trait Info
object Info {
final case class RenameColumn(column: String, newName: String) extends Info
final case class DeleteColumn(column: String) extends Info
final case class MoveColumn(column: String, newIndex: BigInt) extends Info
final case class ChangeSeparator(newSeparator: String) extends Info
final case class Replicate(newSeparators: ::[String]) extends Info
final case class ToJson(pretty: Boolean, outputJson: Path) extends Info
}
}

108. Define Subcommands
themselves

109. Define Subcommands themselves
import zio.cli._
// We'll define the `rename-column` subcommand first
// Which needs the following options:
// - column
// - new-name
// - separator
// Let's create the Options we'll need
val columnOption: Options[String] = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newNameOption: Options[String] = Options.text(name = "new-name").alias("n") ?? "New column name."
val separatorOption: Options[String] = Options.text("separator").alias("s").withDefault(",") ?? "Separator string." // Optional parameters with default values!

110. Define Subcommands themselves
import zio.cli._
// We'll define the `rename-column` subcommand first
// Which needs the following options:
// - column
// - new-name
// - separator
// Let's create the Options we'll need
val columnOption: Options[String] = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newNameOption: Options[String] = Options.text(name = "new-name").alias("n") ?? "New column name."
val separatorOption: Options[String] = Options.text("separator").alias("s").withDefault(",") ?? "Separator string." // Optional parameters with default values!

111. Define Subcommands themselves
import zio.cli._
// We'll define the `rename-column` subcommand first
// Which needs the following options:
// - column
// - new-name
// - separator
// Let's create the Options we'll need
val columnOption: Options[String] = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newNameOption: Options[String] = Options.text(name = "new-name").alias("n") ?? "New column name."
val separatorOption: Options[String] = Options.text("separator").alias("s").withDefault(",") ?? "Separator string." // Optional parameters with default values!

112. Define Subcommands themselves
import zio.cli._
// We'll define the `rename-column` subcommand first
// Which needs the following options:
// - column
// - new-name
// - separator
// Let's create the Options we'll need
val columnOption: Options[String] = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newNameOption: Options[String] = Options.text(name = "new-name").alias("n") ?? "New column name."
val separatorOption: Options[String] = Options.text("separator").alias("s").withDefault(",") ?? "Separator string." // Optional parameters with default values!

113. Define Subcommands themselves
import zio.cli._
// We'll define the `rename-column` subcommand first
// Which needs the following options:
// - column
// - new-name
// - separator
// Let's create the Options we'll need
val columnOption: Options[String] = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newNameOption: Options[String] = Options.text(name = "new-name").alias("n") ?? "New column name."
val separatorOption: Options[String] = Options.text("separator").alias("s").withDefault(",") ?? "Separator string." // Optional parameters with default values!

114. Define Subcommands themselves
import zio.cli._
// We'll define the `rename-column` subcommand first
// Which needs the following options:
// - column
// - new-name
// - separator
// Let's create the Options we'll need
val columnOption: Options[String] = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newNameOption: Options[String] = Options.text(name = "new-name").alias("n") ?? "New column name."
val separatorOption: Options[String] = Options.text("separator").alias("s").withDefault(",") ?? "Separator string." // Optional parameters with default values!

115. Define Subcommands themselves
import zio.cli._
// We'll define the `rename-column` subcommand first
// Which needs the following options:
// - column
// - new-name
// - separator
// Let's create the Options we'll need
val columnOption: Options[String] = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newNameOption: Options[String] = Options.text(name = "new-name").alias("n") ?? "New column name."
val separatorOption: Options[String] = Options.text("separator").alias("s").withDefault(",") ?? "Separator string." // Optional parameters with default values!

116. Define Subcommands themselves
import zio.cli._
// The `rename-column` subcommand needs the following args:
// - input-csv
// Let's create the Args we'll need
val inputCsvArg: Args[Path] = Args.file("input-csv", Exists.Yes) ?? "The input CSV file." // Impure Validation in action!

117. Define Subcommands themselves
import zio.cli._
// The `rename-column` subcommand needs the following args:
// - input-csv
// Let's create the Args we'll need
val inputCsvArg: Args[Path] = Args.file("input-csv", Exists.Yes) ?? "The input CSV file." // Impure Validation in action!

118. Define Subcommands themselves
import zio.cli._
// The `rename-column` subcommand needs the following args:
// - input-csv
// Let's create the Args we'll need
val inputCsvArg: Args[Path] = Args.file("input-csv", Exists.Yes) ?? "The input CSV file." // Impure Validation in action!

119. Define Subcommands themselves
import zio.cli._
// The `rename-column` subcommand needs the following args:
// - input-csv
// Let's create the Args we'll need
val inputCsvArg: Args[Path] = Args.file("input-csv", Exists.Yes) ?? "The input CSV file." // Impure Validation in action!

120. Define Subcommands themselves
import zio.cli._
// Options
val columnOption: Options[String] = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newNameOption: Options[String] = Options.text(name = "new-name").alias("n") ?? "New column name."
val separatorOption: Options[String] = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg: Args[Path] = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the rename-column Command
val renameColumn: Command[((String, String, String), Path)] =
Command(
name = "rename-column",
options = columnOption ++ newNameOption ++ separatorOption, // It's very easy to compose Options!
args = inputCsvArg
)
.withHelp("Rename a column of the given CSV file.")

121. Define Subcommands themselves
import zio.cli._
// Options
val columnOption: Options[String] = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newNameOption: Options[String] = Options.text(name = "new-name").alias("n") ?? "New column name."
val separatorOption: Options[String] = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg: Args[Path] = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the rename-column Command
val renameColumn: Command[((String, String, String), Path)] =
Command(
name = "rename-column",
options = columnOption ++ newNameOption ++ separatorOption, // It's very easy to compose Options!
args = inputCsvArg
)
.withHelp("Rename a column of the given CSV file.")

122. Define Subcommands themselves
import zio.cli._
// Options
val columnOption: Options[String] = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newNameOption: Options[String] = Options.text(name = "new-name").alias("n") ?? "New column name."
val separatorOption: Options[String] = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg: Args[Path] = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the rename-column Command
val renameColumn: Command[((String, String, String), Path)] =
Command(
name = "rename-column",
options = columnOption ++ newNameOption ++ separatorOption, // It's very easy to compose Options!
args = inputCsvArg
)
.withHelp("Rename a column of the given CSV file.")

123. Define Subcommands themselves
import zio.cli._
// Options
val columnOption: Options[String] = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newNameOption: Options[String] = Options.text(name = "new-name").alias("n") ?? "New column name."
val separatorOption: Options[String] = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg: Args[Path] = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the rename-column Command
val renameColumn: Command[((String, String, String), Path)] =
Command(
name = "rename-column",
options = columnOption ++ newNameOption ++ separatorOption, // It's very easy to compose Options!
args = inputCsvArg
)
.withHelp("Rename a column of the given CSV file.")

124. Define Subcommands themselves
import zio.cli._
// Options
val columnOption: Options[String] = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newNameOption: Options[String] = Options.text(name = "new-name").alias("n") ?? "New column name."
val separatorOption: Options[String] = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg: Args[Path] = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the rename-column Command
val renameColumn: Command[((String, String, String), Path)] =
Command(
name = "rename-column",
options = columnOption ++ newNameOption ++ separatorOption, // It's very easy to compose Options!
args = inputCsvArg
)
.withHelp("Rename a column of the given CSV file.")

125. Define Subcommands themselves
import zio.cli._
// Options
val columnOption: Options[String] = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newNameOption: Options[String] = Options.text(name = "new-name").alias("n") ?? "New column name."
val separatorOption: Options[String] = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg: Args[Path] = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the rename-column Command
val renameColumn: Command[((String, String, String), Path)] =
Command(
name = "rename-column",
options = columnOption ++ newNameOption ++ separatorOption, // It's very easy to compose Options!
args = inputCsvArg
)
.withHelp("Rename a column of the given CSV file.")

126. Define Subcommands themselves
import zio.cli._
// Options
val columnOption: Options[String] = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newNameOption: Options[String] = Options.text(name = "new-name").alias("n") ?? "New column name."
val separatorOption: Options[String] = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg: Args[Path] = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the rename-column Command
val renameColumn: Command[((String, String, String), Path)] =
Command(
name = "rename-column",
options = columnOption ++ newNameOption ++ separatorOption, // It's very easy to compose Options!
args = inputCsvArg
)
.withHelp("Rename a column of the given CSV file.")

127. Define Subcommands themselves
import zio.cli._
// Options
val columnOption: Options[String] = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newNameOption: Options[String] = Options.text(name = "new-name").alias("n") ?? "New column name."
val separatorOption: Options[String] = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg: Args[Path] = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the rename-column Command
val renameColumn: Command[((String, String, String), Path)] =
Command(
name = "rename-column",
options = columnOption ++ newNameOption ++ separatorOption, // It's very easy to compose Options!
args = inputCsvArg
)
.withHelp("Rename a column of the given CSV file.")

128. Define Subcommands themselves
import zio.cli._
// Options
val columnOption: Options[String] = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newNameOption: Options[String] = Options.text(name = "new-name").alias("n") ?? "New column name."
val separatorOption: Options[String] = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg: Args[Path] = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the rename-column Command
val renameColumn: Command[((String, String, String), Path)] =
Command(
name = "rename-column",
options = columnOption ++ newNameOption ++ separatorOption, // It's very easy to compose Options!
args = inputCsvArg
)
.withHelp("Rename a column of the given CSV file.")

129. Define Subcommands themselves
import zio.cli._
// Options
val columnOption: Options[String] = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newNameOption: Options[String] = Options.text(name = "new-name").alias("n") ?? "New column name."
val separatorOption: Options[String] = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg: Args[Path] = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the rename-column Command
val renameColumn: Command[((String, String, String), Path)] =
Command(
name = "rename-column",
options = columnOption ++ newNameOption ++ separatorOption, // It's very easy to compose Options!
args = inputCsvArg
)
.withHelp("Rename a column of the given CSV file.")

130. Define Subcommands themselves
import zio.cli._
// Options
val columnOption: Options[String] = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newNameOption: Options[String] = Options.text(name = "new-name").alias("n") ?? "New column name."
val separatorOption: Options[String] = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg: Args[Path] = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the rename-column Command
val renameColumn: Command[((String, String, String), Path)] =
Command(
name = "rename-column",
options = columnOption ++ newNameOption ++ separatorOption, // It's very easy to compose Options!
args = inputCsvArg
)
.withHelp("Rename a column of the given CSV file.")

131. Define Subcommands themselves
import zio.cli._
// Options
val columnOption: Options[String] = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newNameOption: Options[String] = Options.text(name = "new-name").alias("n") ?? "New column name."
val separatorOption: Options[String] = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg: Args[Path] = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the rename-column Command
val renameColumn: Command[((String, String, String), Path)] =
Command(
name = "rename-column",
options = columnOption ++ newNameOption ++ separatorOption, // It's very easy to compose Options!
args = inputCsvArg
)
.withHelp("Rename a column of the given CSV file.")

132. Define Subcommands themselves
// Improve the rename-column Command
val renameColumn: Command[Subcommand] =
Command(
name = "rename-column",
options = columnOption ++ newNameOption ++ separatorOption,
args = inputCsvArg
)
.withHelp("Rename a column of the given CSV file.")
.map { case ((column, newName, separator), inputCsv) =>
Subcommand(separator, inputCsv, Subcommand.Info.RenameColumn(column, newName))
}

133. Define Subcommands themselves
// Improve the rename-column Command
val renameColumn: Command[Subcommand] =
Command(
name = "rename-column",
options = columnOption ++ newNameOption ++ separatorOption,
args = inputCsvArg
)
.withHelp("Rename a column of the given CSV file.")
.map { case ((column, newName, separator), inputCsv) =>
Subcommand(separator, inputCsv, Subcommand.Info.RenameColumn(column, newName))
}

134. Define Subcommands themselves
// Improve the rename-column Command
val renameColumn: Command[Subcommand] =
Command(
name = "rename-column",
options = columnOption ++ newNameOption ++ separatorOption,
args = inputCsvArg
)
.withHelp("Rename a column of the given CSV file.")
.map { case ((column, newName, separator), inputCsv) =>
Subcommand(separator, inputCsv, Subcommand.Info.RenameColumn(column, newName))
}

135. Define Subcommands themselves
// Improve the rename-column Command
val renameColumn: Command[Subcommand] =
Command(
name = "rename-column",
options = columnOption ++ newNameOption ++ separatorOption,
args = inputCsvArg
)
.withHelp("Rename a column of the given CSV file.")
.map { case ((column, newName, separator), inputCsv) =>
Subcommand(separator, inputCsv, Subcommand.Info.RenameColumn(column, newName))
}

136. Define Subcommands themselves
// Improve the rename-column Command
val renameColumn: Command[Subcommand] =
Command(
name = "rename-column",
options = columnOption ++ newNameOption ++ separatorOption,
args = inputCsvArg
)
.withHelp("Rename a column of the given CSV file.")
.map { case ((column, newName, separator), inputCsv) =>
Subcommand(separator, inputCsv, Subcommand.Info.RenameColumn(column, newName))
}

137. Define Subcommands themselves
// Improve the rename-column Command
val renameColumn: Command[Subcommand] =
Command(
name = "rename-column",
options = columnOption ++ newNameOption ++ separatorOption,
args = inputCsvArg
)
.withHelp("Rename a column of the given CSV file.")
.map { case ((column, newName, separator), inputCsv) =>
Subcommand(separator, inputCsv, Subcommand.Info.RenameColumn(column, newName))
}

138. Define Subcommands themselves
import zio.cli._
// Options
val columnOption = Options.text(name = "column").alias("c") ?? "Name of the input column."
val separatorOption = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the delete-column Command
val deleteColumn =
Command(name = "delete-column", options = columnOption ++ separatorOption, args = inputCsvArg)
.withHelp("Delete a column of the given CSV file.")
.map { case ((column, separator), inputCsv) =>
Subcommand(separator, inputCsv, Subcommand.Info.DeleteColumn(column))
}

139. Define Subcommands themselves
import zio.cli._
// Options
val columnOption = Options.text(name = "column").alias("c") ?? "Name of the input column."
val separatorOption = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the delete-column Command
val deleteColumn =
Command(name = "delete-column", options = columnOption ++ separatorOption, args = inputCsvArg)
.withHelp("Delete a column of the given CSV file.")
.map { case ((column, separator), inputCsv) =>
Subcommand(separator, inputCsv, Subcommand.Info.DeleteColumn(column))
}

140. Define Subcommands themselves
import zio.cli._
// Options
val columnOption = Options.text(name = "column").alias("c") ?? "Name of the input column."
val separatorOption = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the delete-column Command
val deleteColumn =
Command(name = "delete-column", options = columnOption ++ separatorOption, args = inputCsvArg)
.withHelp("Delete a column of the given CSV file.")
.map { case ((column, separator), inputCsv) =>
Subcommand(separator, inputCsv, Subcommand.Info.DeleteColumn(column))
}

141. Define Subcommands themselves
import zio.cli._
// Options
val columnOption = Options.text(name = "column").alias("c") ?? "Name of the input column."
val separatorOption = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the delete-column Command
val deleteColumn =
Command(name = "delete-column", options = columnOption ++ separatorOption, args = inputCsvArg)
.withHelp("Delete a column of the given CSV file.")
.map { case ((column, separator), inputCsv) =>
Subcommand(separator, inputCsv, Subcommand.Info.DeleteColumn(column))
}

142. Define Subcommands themselves
import zio.cli._
// Options
val columnOption = Options.text(name = "column").alias("c") ?? "Name of the input column."
val separatorOption = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the delete-column Command
val deleteColumn =
Command(name = "delete-column", options = columnOption ++ separatorOption, args = inputCsvArg)
.withHelp("Delete a column of the given CSV file.")
.map { case ((column, separator), inputCsv) =>
Subcommand(separator, inputCsv, Subcommand.Info.DeleteColumn(column))
}

143. Define Subcommands themselves
import zio.cli._
// Options
val columnOption = Options.text(name = "column").alias("c") ?? "Name of the input column."
val separatorOption = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the delete-column Command
val deleteColumn =
Command(name = "delete-column", options = columnOption ++ separatorOption, args = inputCsvArg)
.withHelp("Delete a column of the given CSV file.")
.map { case ((column, separator), inputCsv) =>
Subcommand(separator, inputCsv, Subcommand.Info.DeleteColumn(column))
}

144. Define Subcommands themselves
import zio.cli._
// Options
val columnOption = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newIndexOption = Options.integer("new-index").alias("i") ?? "New column index." // Pure Validation in action!
val separatorOption = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the move-column Command
val moveColumn =
Command(name = "move-column", options = columnOption ++ newIndexOption ++ separatorOption, args = inputCsvArg)
.withHelp("Move a column of the given CSV file.")
.map { case ((column, newIndex, separator), inputCsv) =>
Subcommand(separator, inputCsv, Subcommand.Info.MoveColumn(column, newIndex))
}

145. Define Subcommands themselves
import zio.cli._
// Options
val columnOption = Options.text(name = "column").alias("c") ?? "Name of the input column."
val newIndexOption = Options.integer("new-index").alias("i") ?? "New column index." // Pure Validation in action!
val separatorOption = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the move-column Command
val moveColumn =
Command(name = "move-column", options = columnOption ++ newIndexOption ++ separatorOption, args = inputCsvArg)
.withHelp("Move a column of the given CSV file.")
.map { case ((column, newIndex, separator), inputCsv) =>
Subcommand(separator, inputCsv, Subcommand.Info.MoveColumn(column, newIndex))
}

146. Define Subcommands themselves
import zio.cli._
// Options
val separatorOption = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
val newSeparatorOption = Options.text("new-separator") ?? "New separator string." // You don't always need to define an alias!
// Args
val inputCsvArg = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the change-separator Command
val changeSeparator =
Command(name = "change-separator", options = separatorOption ++ newSeparatorOption, args = inputCsvArg)
.withHelp("Change the separator string of the given CSV file.")
.map { case ((separator, newSeparator), inputCsv) =>
Subcommand(separator, inputCsv, Subcommand.Info.ChangeSeparator(newSeparator))
}

147. Define Subcommands themselves
import zio.cli._
// Options
val separatorOption = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
val newSeparatorOption = Options.text("new-separator") ?? "New separator string." // You don't always need to define an alias!
// Args
val inputCsvArg = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
// Create the change-separator Command
val changeSeparator =
Command(name = "change-separator", options = separatorOption ++ newSeparatorOption, args = inputCsvArg)
.withHelp("Change the separator string of the given CSV file.")
.map { case ((separator, newSeparator), inputCsv) =>
Subcommand(separator, inputCsv, Subcommand.Info.ChangeSeparator(newSeparator))
}

148. Define Subcommands themselves
import zio.cli._
// Options
val separatorOption = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg: Args[String] = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
val newSeparatorsArg: Args[::[String]] = Args.text("new-separator").repeat1 ?? "The new separators for the CSV replicas." // Varargs in action!
// Create the replicate Command
val replicate =
Command(
name = "replicate",
options = separatorOption,
args = inputCsvArg ++ newSeparatorsArg // It's very easy to compose Args!
)
.withHelp("Replicate the given CSV file with the given separators")
.map { case (separator, (inputCsv, newSeparators)) =>
Subcommand(separator, inputCsv, Subcommand.Info.Replicate(newSeparators))
}

149. Define Subcommands themselves
import zio.cli._
// Options
val separatorOption = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg: Args[String] = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
val newSeparatorsArg: Args[::[String]] = Args.text("new-separator").repeat1 ?? "The new separators for the CSV replicas." // Varargs in action!
// Create the replicate Command
val replicate =
Command(
name = "replicate",
options = separatorOption,
args = inputCsvArg ++ newSeparatorsArg // It's very easy to compose Args!
)
.withHelp("Replicate the given CSV file with the given separators")
.map { case (separator, (inputCsv, newSeparators)) =>
Subcommand(separator, inputCsv, Subcommand.Info.Replicate(newSeparators))
}

150. Define Subcommands themselves
import zio.cli._
// Options
val separatorOption = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg: Args[String] = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
val newSeparatorsArg: Args[::[String]] = Args.text("new-separator").repeat1 ?? "The new separators for the CSV replicas." // Varargs in action!
// Create the replicate Command
val replicate =
Command(
name = "replicate",
options = separatorOption,
args = inputCsvArg ++ newSeparatorsArg // It's very easy to compose Args!
)
.withHelp("Replicate the given CSV file with the given separators")
.map { case (separator, (inputCsv, newSeparators)) =>
Subcommand(separator, inputCsv, Subcommand.Info.Replicate(newSeparators))
}

151. Define Subcommands themselves
import zio.cli._
// Options
val prettyOption = Options.boolean(name = "pretty").alias("p") ?? "Pretty format output JSON." // Flags in action!
val separatorOption = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
val outputJsonArg = Args.file("output-json", Exists.No) ?? "The output JSON file." // You can require that a file does not exist!
// Create the to-json Command
val toJson =
Command(name = "to-json", options = prettyOption ++ separatorOption, args = inputCsvArg ++ outputJsonArg)
.withHelp("Convert the given CSV file to JSON.")
.map { case ((pretty, separator), (inputCsv, outputJson)) =>
Subcommand(separator, inputCsv, Subcommand.Info.ToJson(pretty, outputJson))
}

152. Define Subcommands themselves
import zio.cli._
// Options
val prettyOption = Options.boolean(name = "pretty").alias("p") ?? "Pretty format output JSON." // Flags in action!
val separatorOption = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
val outputJsonArg = Args.file("output-json", Exists.No) ?? "The output JSON file." // You can require that a file does not exist!
// Create the to-json Command
val toJson =
Command(name = "to-json", options = prettyOption ++ separatorOption, args = inputCsvArg ++ outputJsonArg)
.withHelp("Convert the given CSV file to JSON.")
.map { case ((pretty, separator), (inputCsv, outputJson)) =>
Subcommand(separator, inputCsv, Subcommand.Info.ToJson(pretty, outputJson))
}

153. Define Subcommands themselves
import zio.cli._
// Options
val prettyOption = Options.boolean(name = "pretty").alias("p") ?? "Pretty format output JSON." // Flags in action!
val separatorOption = Options.text("separator").alias("s").withDefault(",") ?? "Separator string."
// Args
val inputCsvArg = Args.file("input-csv", Exists.Yes) ?? "The input CSV file."
val outputJsonArg = Args.file("output-json", Exists.No) ?? "The output JSON file." // You can require that a file does not exist!
// Create the to-json Command
val toJson =
Command(name = "to-json", options = prettyOption ++ separatorOption, args = inputCsvArg ++ outputJsonArg)
.withHelp("Convert the given CSV file to JSON.")
.map { case ((pretty, separator), (inputCsv, outputJson)) =>
Subcommand(separator, inputCsv, Subcommand.Info.ToJson(pretty, outputJson))
}

154. Compose
Subcommands under
a Root Command

155. Compose Subcommands under a Root
Command
val csvUtil: Command[Subcommand] =
Command(name = "csv-util", options = Options.none, args = Args.none)
.subcommands(
renameColumn,
deleteColumn,
moveColumn,
changeSeparator,
replicate,
toJson
)

156. Compose Subcommands under a Root
Command
val csvUtil: Command[Subcommand] =
Command(name = "csv-util", options = Options.none, args = Args.none)
.subcommands(
renameColumn,
deleteColumn,
moveColumn,
changeSeparator,
replicate,
toJson
)

157. Compose Subcommands under a Root
Command
val csvUtil: Command[Subcommand] =
Command(name = "csv-util", options = Options.none, args = Args.none)
.subcommands(
renameColumn,
deleteColumn,
moveColumn,
changeSeparator,
replicate,
toJson
)

158. Create a CLIApp that
assigns
Subcommands to
Handlers

159. Create a CLIApp that assigns
Subcommands to Handlers
import zio.cli._
object CsvUtil extends ZIOCliDefault {
// Options, Args, Subcommands and Root Command
...
val cliApp =
CliApp.make(
name = "CSV Util",
version = "0.0.1",
summary = text("CLI to some CSV utilities"),
footer = HelpDoc.p("©Copyright 2022"),
command = csvUtil // Root command
) { case Subcommand(separator, inputCsv, info) =>
info match {
case Info.RenameColumn(column, newName) =>
Console.printLine {
s"Handling rename-column command with column=$column, new-name=$newName, separator=$separator, input-csv=$inputCsv"
}
...
}
}
}

160. Create a CLIApp that assigns
Subcommands to Handlers
import zio.cli._
object CsvUtil extends ZIOCliDefault {
// Options, Args, Subcommands and Root Command
...
val cliApp =
CliApp.make(
name = "CSV Util",
version = "0.0.1",
summary = text("CLI to some CSV utilities"),
footer = HelpDoc.p("©Copyright 2022"),
command = csvUtil // Root command
) { case Subcommand(separator, inputCsv, info) =>
info match {
case Info.RenameColumn(column, newName) =>
Console.printLine {
s"Handling rename-column command with column=$column, new-name=$newName, separator=$separator, input-csv=$inputCsv"
}
...
}
}
}

161. Create a CLIApp that assigns
Subcommands to Handlers
import zio.cli._
object CsvUtil extends ZIOCliDefault {
// Options, Args, Subcommands and Root Command
...
val cliApp =
CliApp.make(
name = "CSV Util",
version = "0.0.1",
summary = text("CLI to some CSV utilities"),
footer = HelpDoc.p("©Copyright 2022"),
command = csvUtil // Root command
) { case Subcommand(separator, inputCsv, info) =>
info match {
case Info.RenameColumn(column, newName) =>
Console.printLine {
s"Handling rename-column command with column=$column, new-name=$newName, separator=$separator, input-csv=$inputCsv"
}
...
}
}
}

162. Create a CLIApp that assigns
Subcommands to Handlers
import zio.cli._
object CsvUtil extends ZIOCliDefault {
// Options, Args, Subcommands and Root Command
...
val cliApp =
CliApp.make(
name = "CSV Util",
version = "0.0.1",
summary = text("CLI to some CSV utilities"),
footer = HelpDoc.p("©Copyright 2022"),
command = csvUtil // Root command
) { case Subcommand(separator, inputCsv, info) =>
info match {
case Info.RenameColumn(column, newName) =>
Console.printLine {
s"Handling rename-column command with column=$column, new-name=$newName, separator=$separator, input-csv=$inputCsv"
}
...
}
}
}

163. Create a CLIApp that assigns
Subcommands to Handlers
import zio.cli._
object CsvUtil extends ZIOCliDefault {
// Options, Args, Subcommands and Root Command
...
val cliApp =
CliApp.make(
name = "CSV Util",
version = "0.0.1",
summary = text("CLI to some CSV utilities"),
footer = HelpDoc.p("©Copyright 2022"),
command = csvUtil // Root command
) { case Subcommand(separator, inputCsv, info) =>
info match {
case Info.RenameColumn(column, newName) =>
Console.printLine {
s"Handling rename-column command with column=$column, new-name=$newName, separator=$separator, input-csv=$inputCsv"
}
...
}
}
}

164. Create a CLIApp that assigns
Subcommands to Handlers
import zio.cli._
object CsvUtil extends ZIOCliDefault {
// Options, Args, Subcommands and Root Command
...
val cliApp =
CliApp.make(
name = "CSV Util",
version = "0.0.1",
summary = text("CLI to some CSV utilities"),
footer = HelpDoc.p("©Copyright 2022"),
command = csvUtil // Root command
) { case Subcommand(separator, inputCsv, info) =>
info match {
case Info.RenameColumn(column, newName) =>
Console.printLine {
s"Handling rename-column command with column=$column, new-name=$newName, separator=$separator, input-csv=$inputCsv"
}
...
}
}
}

165. Create a CLIApp that assigns
Subcommands to Handlers
import zio.cli._
object CsvUtil extends ZIOCliDefault {
// Options, Args, Subcommands and Root Command
...
val cliApp =
CliApp.make(
name = "CSV Util",
version = "0.0.1",
summary = text("CLI to some CSV utilities"),
footer = HelpDoc.p("©Copyright 2022"),
command = csvUtil // Root command
) { case Subcommand(separator, inputCsv, info) =>
info match {
case Info.RenameColumn(column, newName) =>
Console.printLine {
s"Handling rename-column command with column=$column, new-name=$newName, separator=$separator, input-csv=$inputCsv"
}
...
}
}
}

166. Create a CLIApp that assigns
Subcommands to Handlers
import zio.cli._
object CsvUtil extends ZIOCliDefault {
// Options, Args, Subcommands and Root Command
...
val cliApp =
CliApp.make(
name = "CSV Util",
version = "0.0.1",
summary = text("CLI to some CSV utilities"),
footer = HelpDoc.p("©Copyright 2022"),
command = csvUtil // Root command
) { case Subcommand(separator, inputCsv, info) =>
info match {
case Info.RenameColumn(column, newName) =>
Console.printLine {
s"Handling rename-column command with column=$column, new-name=$newName, separator=$separator, input-csv=$inputCsv"
}
...
}
}
}

167. Create a CLIApp that assigns
Subcommands to Handlers
import zio.cli._
object CsvUtil extends ZIOCliDefault {
// Options, Args, Subcommands and Root Command
...
val cliApp =
CliApp.make(
name = "CSV Util",
version = "0.0.1",
summary = text("CLI to some CSV utilities"),
footer = HelpDoc.p("©Copyright 2022"),
command = csvUtil // Root command
) { case Subcommand(separator, inputCsv, info) =>
info match {
case Info.RenameColumn(column, newName) =>
Console.printLine {
s"Handling rename-column command with column=$column, new-name=$newName, separator=$separator, input-csv=$inputCsv"
}
...
}
}
}

168. Create a CLIApp that assigns
Subcommands to Handlers
import zio.cli._
object CsvUtil extends ZIOCliDefault {
// Options, Args, Subcommands and Root Command
...
val cliApp =
CliApp.make(
name = "CSV Util",
version = "0.0.1",
summary = text("CLI to some CSV utilities"),
footer = HelpDoc.p("©Copyright 2022"),
command = csvUtil // Root command
) { case Subcommand(separator, inputCsv, info) =>
info match {
case Info.RenameColumn(column, newName) =>
Console.printLine {
s"Handling rename-column command with column=$column, new-name=$newName, separator=$separator, input-csv=$inputCsv"
}
...
}
}
}

169. Create a CLIApp that assigns
Subcommands to Handlers
import zio.cli._
object CsvUtil extends ZIOCliDefault {
// Options, Args, Subcommands and Root Command
...
val cliApp =
CliApp.make(
name = "CSV Util",
version = "0.0.1",
summary = text("CLI to some CSV utilities"),
footer = HelpDoc.p("©Copyright 2022"),
command = csvUtil // Root command
) { case Subcommand(separator, inputCsv, info) =>
info match {
case Info.RenameColumn(column, newName) =>
Console.printLine {
s"Handling rename-column command with column=$column, new-name=$newName, separator=$separator, input-csv=$inputCsv"
}
...
}
}
}

170. Create a CLIApp that assigns
Subcommands to Handlers
import zio.cli._
object CsvUtil extends ZIOCliDefault {
// Options, Args, Subcommands and Root Command
...
val cliApp =
CliApp.make(
name = "CSV Util",
version = "0.0.1",
summary = text("CLI to some CSV utilities"),
footer = HelpDoc.p("©Copyright 2022"),
command = csvUtil // Root command
) { case Subcommand(separator, inputCsv, info) =>
info match {
case Info.RenameColumn(column, newName) =>
Console.printLine {
s"Handling rename-column command with column=$column, new-name=$newName, separator=$separator, input-csv=$inputCsv"
}
...
}
}
}

171. Installing the
application

172. Installing the application

173. Installing the application
✓ For installing your CLI application, ZIO CLI includes an
installer script that:

174. Installing the application
✓ For installing your CLI application, ZIO CLI includes an
installer script that:
✓Generates a GraalVM native image for you

175. Installing the application
✓ For installing your CLI application, ZIO CLI includes an
installer script that:
✓Generates a GraalVM native image for you
✓Installs this as an executable on your machine

177. Touring the CSV-Util
application!

178. Executing the root command with
no options/arguments

180. Executing the root command with
the --help flag

182. Executing a subcommand with
the --help flag

184. Executing a subcommand with
missing args

186. Executing a subcommand
successfully

188. Executing a subcommand with
different variations in options

190. Grouping several flags together

192. Pure validation of options/args

194. Impure validation of options/args

196. Varargs

199. Automatic misspellings detection
and correction!

201. Shell-integrated autocompletion!

202. Shell-integrated autocompletion!
For enabling autocompletion for your CLI app, a shell-
completion script is generated like this:
# Generates a shell-completion.sh script
$ csv-util --shell-completion-script `which csv-util` --shell-type bash
# Enables completions
$ source completion-script.sh

203. Shell-integrated autocompletion!
For enabling autocompletion for your CLI app, a shell-
completion script is generated like this:
# Generates a shell-completion.sh script
$ csv-util --shell-completion-script `which csv-util` --shell-type bash
# Enables completions
$ source completion-script.sh

204. Shell-integrated autocompletion!
For enabling autocompletion for your CLI app, a shell-
completion script is generated like this:
# Generates a shell-completion.sh script
$ csv-util --shell-completion-script `which csv-util` --shell-type bash
# Enables completions
$ source completion-script.sh

205. Shell-integrated autocompletion!
For enabling autocompletion for your CLI app, a shell-
completion script is generated like this:
# Generates a shell-completion.sh script
$ csv-util --shell-completion-script `which csv-util` --shell-type bash
# Enables completions
$ source completion-script.sh

206. Shell-integrated autocompletion!
For enabling autocompletion for your CLI app, a shell-
completion script is generated like this:
# Generates a shell-completion.sh script
$ csv-util --shell-completion-script `which csv-util` --shell-type bash
# Enables completions
$ source completion-script.sh

208. Wizard mode for the root
command!

210. Wizard mode for a subcommand!

212. Comparing ZIO CLI to
other libraries

213. Comparing ZIO CLI to other libraries
Annotations for
customization
Autocorrection Autocompletion Wizard mode
decline ❌ ❌ ❌ ❌
mainargs ✅ ❌ ❌ ❌
case-app ✅ ❌ ❌ ❌
scallop ❌ ❌ ❌ ❌
scopt ❌ ❌ ❌ ❌
optparse ❌ ❌ ❌ ❌
zio-cli ❌ (Coming soon!) ✅ ✅ ✅

214. Summary

215. Summary

216. Summary
✓ CLI apps are very useful for non-devs to interact with
your applications

217. Summary
✓ CLI apps are very useful for non-devs to interact with
your applications
✓ However, writing production-grade CLI apps is hard

218. Summary
✓ CLI apps are very useful for non-devs to interact with
your applications
✓ However, writing production-grade CLI apps is hard
✓ Actually, it doesn't have to be hard, not with ZIO CLI!!!

219. Special thanks

220. Special thanks
✓ Ziverge for organizing this
conference

221. Special thanks
✓ Ziverge for organizing this
conference
✓ Scalac for sponsoring

222. Special thanks
✓ Ziverge for organizing this
conference
✓ Scalac for sponsoring
✓ John De Goes for guidance and
support

223. Contact me
@jorvasquez2301
jorge-vasquez-2301
jorge.vasquez@scalac.io