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# Ruby Command-Line Options

## About the Examples

Some examples here use command-line option `-e`, which passes the Ruby code to be executed on the command line itself:

    $ ruby -e 'puts "Hello, World."'

Some examples here assume that file `desiderata.txt` exists:

    $ cat desiderata.txt
    Go placidly amid the noise and the haste,
    and remember what peace there may be in silence.
    As far as possible, without surrender,
    be on good terms with all persons.

## Options

### `-0`: Set `$/` (Input Record Separator)

Option `-0` defines the input record separator `$/` for the invoked Ruby program.

The optional argument to the option must be octal digits, each in the range `0..7`; these digits are prefixed with digit `0` to form an octal value.

If no argument is given, the input record separator is `0x00`.

If an argument is given, it must immediately follow the option (no intervening whitespace or equal-sign character `'='`); argument values:

- `0`: the input record separator is `''`; see Special Line Separator Values.

- In range `(1..0377)`: the input record separator `$/` is set to the character value of the argument.

- Any other octal value: the input record separator is `nil`.

Examples:

    $ ruby -0 -e 'p $/'
    "\x00"
    ruby -00 -e 'p $/'
    ""
    $ ruby -012 -e 'p $/'
    "\n"
    $ ruby -015 -e 'p $/'
    "\r"
    $ ruby -0377 -e 'p $/'
    "\xFF"
    $ ruby -0400 -e 'p $/'
    nil

See also:

- Option -a: Split input lines into fields.

- Option -F: Set input field separator.

- Option -l: Set output record separator; chop lines.

- Option -n: Run program in `gets` loop.

- Option -p: `-n`, with printing.

### `-a`: Split Input Lines into Fields

Option `-a`, when given with either of options `-n` or `-p`, splits the string at `$_` into an array of strings at `$F`:

    $ ruby -an -e 'p $F' desiderata.txt
    ["Go", "placidly", "amid", "the", "noise", "and", "the", "haste,"]
    ["and", "remember", "what", "peace", "there", "may", "be", "in", "silence."]
    ["As", "far", "as", "possible,", "without", "surrender,"]
    ["be", "on", "good", "terms", "with", "all", "persons."]

For the splitting, the default record separator is `$/`, and the default field separator is `$;`.

See also:

- Option -0: Set `$/` (input record separator).

- Option -F: Set input field separator.

- Option -l: Set output record separator; chop lines.

- Option -n: Run program in `gets` loop.

- Option -p: `-n`, with printing.

### `-c`: Check Syntax

Option `-c` specifies that the specified Ruby program should be checked for syntax, but not actually executed:

    $ ruby -e 'puts "Foo"'
    Foo
    $ ruby -c -e 'puts "Foo"'
    Syntax OK

### `-C`: Set Working Directory

The argument to option `-C` specifies a working directory for the invoked Ruby program; does not change the working directory for the current process:

    $ basename `pwd`
    ruby
    $ ruby -C lib -e 'puts File.basename(Dir.pwd)'
    lib
    $ basename `pwd`
    ruby

Whitespace between the option and its argument may be omitted.

### `-d`: Set `$DEBUG` to `true`

Some code in (or called by) the Ruby program may include statements or blocks conditioned by the global variable `$DEBUG` (e.g., `if $DEBUG`); these commonly write to `$stdout` or `$stderr`.

The default value for `$DEBUG` is `false`; option `-d` sets it to `true`:

    $ ruby -e 'p $DEBUG'
    false
    $ ruby -d -e 'p $DEBUG'
    true

Option `--debug` is an alias for option `-d`.

### `-e`: Execute Given Ruby Code

Option `-e` requires an argument, which is Ruby code to be executed; the option may be given more than once:

    $ ruby -e 'puts "Foo"' -e 'puts "Bar"'
    Foo
    Bar

Whitespace between the option and its argument may be omitted.

The command may include other options, but should not include arguments (which, if given, are ignored).

### `-E`: Set Default Encodings

Option `-E` requires an argument, which specifies either the default external encoding, or both the default external and internal encodings for the invoked Ruby program:

    # No option -E.
    $ ruby -e 'p [Encoding::default_external, Encoding::default_internal]'
    [#<Encoding:UTF-8>, nil]
    # Option -E with default external encoding.
    $ ruby -E cesu-8 -e 'p [Encoding::default_external, Encoding::default_internal]'
    [#<Encoding:CESU-8>, nil]
    # Option -E with default external and internal encodings.
    $ ruby -E utf-8:cesu-8 -e 'p [Encoding::default_external, Encoding::default_internal]'
    [#<Encoding:UTF-8>, #<Encoding:CESU-8>]

Whitespace between the option and its argument may be omitted.

See also:

- Option –external-encoding: Set default external encoding.

- Option –internal-encoding: Set default internal encoding.

Option `--encoding` is an alias for option `-E`.

### `-F`: Set Input Field Separator

Option `-F`, when given with option `-a`, specifies that its argument is to be the input field separator to be used for splitting:

    $ ruby -an -Fs -e 'p $F' desiderata.txt
    ["Go placidly amid the noi", "e and the ha", "te,\n"]
    ["and remember what peace there may be in ", "ilence.\n"]
    ["A", " far a", " po", "", "ible, without ", "urrender,\n"]
    ["be on good term", " with all per", "on", ".\n"]

The argument may be a regular expression:

    $ ruby -an -F'[.,]\s*' -e 'p $F' desiderata.txt
    ["Go placidly amid the noise and the haste"]
    ["and remember what peace there may be in silence"]
    ["As far as possible", "without surrender"]
    ["be on good terms with all persons"]

The argument must immediately follow the option (no intervening whitespace or equal-sign character `'='`).

See also:

- Option -0: Set `$/` (input record separator).

- Option -a: Split input lines into fields.

- Option -l: Set output record separator; chop lines.

- Option -n: Run program in `gets` loop.

- Option -p: `-n`, with printing.

### `-h`: Print Short Help Message

Option `-h` prints a short help message that includes single-hyphen options (e.g. `-I`), and largely omits double-hyphen options (e.g., `--version`).

Arguments and additional options are ignored.

For a longer help message, use option `--help`.

### `-i`: Set ARGF In-Place Mode

Option `-i` sets the ARGF in-place mode for the invoked Ruby program; see `ARGF#inplace_mode=`:

    $ ruby -e 'p ARGF.inplace_mode'
    nil
    $ ruby -i -e 'p ARGF.inplace_mode'
    ""
    $ ruby -i.bak -e 'p ARGF.inplace_mode'
    ".bak"

### `-I`: Add to `$LOAD_PATH`

The argument to option `-I` specifies a directory to be added to the array in global variable `$LOAD_PATH`; the option may be given more than once:

    $ pushd /tmp
    $ ruby -e 'p $LOAD_PATH.size'
    8
    $ ruby -I my_lib -I some_lib -e 'p $LOAD_PATH.size'
    10
    $ ruby -I my_lib -I some_lib -e 'p $LOAD_PATH.take(2)'
    ["/tmp/my_lib", "/tmp/some_lib"]
    $ popd

Whitespace between the option and its argument may be omitted.

### `-l`: Set Output Record Separator; Chop Lines

Option `-l`, when given with option `-n` or `-p`, modifies line-ending processing by:

- Setting global variable output record separator `$\` to the current value of input record separator `$/`; this affects line-oriented output (such a the output from `Kernel#puts`).

- Calling `String#chop!` on each line read.

Without option `-l` (unchopped):

    $ ruby -n -e 'p $_' desiderata.txt
    "Go placidly amid the noise and the haste,\n"
    "and remember what peace there may be in silence.\n"
    "As far as possible, without surrender,\n"
    "be on good terms with all persons.\n"

With option `-l` (chopped):

    $ ruby -ln -e 'p $_' desiderata.txt
    "Go placidly amid the noise and the haste,"
    "and remember what peace there may be in silence."
    "As far as possible, without surrender,"
    "be on good terms with all persons."

See also:

- Option -0: Set `$/` (input record separator).

- Option -a: Split input lines into fields.

- Option -F: Set input field separator.

- Option -n: Run program in `gets` loop.

- Option -p: `-n`, with printing.

### `-n`: Run Program in `gets` Loop

Option `-n` runs your program in a `Kernel#gets` loop:

    while gets
      # Your Ruby code.
    end

Note that `gets` reads the next line and sets global variable `$_` to the last read line:

    $ ruby -n -e 'puts $_' desiderata.txt
    Go placidly amid the noise and the haste,
    and remember what peace there may be in silence.
    As far as possible, without surrender,
    be on good terms with all persons.

See also:

- Option -0: Set `$/` (input record separator).

- Option -a: Split input lines into fields.

- Option -F: Set input field separator.

- Option -l: Set output record separator; chop lines.

- Option -p: `-n`, with printing.

### `-p`: `-n`, with Printing

Option `-p` is like option `-n`, but also prints each line:

    $ ruby -p -e 'puts $_.size' desiderata.txt
    42
    Go placidly amid the noise and the haste,
    49
    and remember what peace there may be in silence.
    39
    As far as possible, without surrender,
    35
    be on good terms with all persons.

See also:

- Option -0: Set `$/` (input record separator).

- Option -a: Split input lines into fields.

- Option -F: Set input field separator.

- Option -l: Set output record separator; chop lines.

- Option -n: Run program in `gets` loop.

### `-r`: Require Library

The argument to option `-r` specifies a library to be required before executing the Ruby program; the option may be given more than once:

    $ ruby -e 'p defined?(JSON); p defined?(CSV)'
    nil
    nil
    $ ruby -r CSV -r JSON -e 'p defined?(JSON); p defined?(CSV)'
    "constant"
    "constant"

Whitespace between the option and its argument may be omitted.

### `-s`: Define Global Variable

Option `-s` specifies that a “custom option” is to define a global variable in the invoked Ruby program:

- The custom option must appear after the program name.

- The custom option must begin with single hyphen (e.g., `-foo`), not two hyphens (e.g., `--foo`).

- The name of the global variable is based on the option name: global variable `$foo` for custom option`-foo`.

- The value of the global variable is the string option argument if given, `true` otherwise.

More than one custom option may be given:

    $ cat t.rb
    p [$foo, $bar]
    $ ruby t.rb
    [nil, nil]
    $ ruby -s t.rb -foo=baz
    ["baz", nil]
    $ ruby -s t.rb -foo
    [true, nil]
    $ ruby -s t.rb -foo=baz -bar=bat
    ["baz", "bat"]

The option may not be used with option -e

### `-S`: Search Directories in `ENV['PATH']`

Option `-S` specifies that the Ruby interpreter is to search (if necessary) the directories whose paths are in the program’s `PATH` environment variable; the program is executed in the shell’s current working directory (not necessarily in the directory where the program is found).

This example uses adds path `'tmp/'` to the `PATH` environment variable:

    $ export PATH=/tmp:$PATH
    $ echo "puts File.basename(Dir.pwd)" > /tmp/t.rb
    $ ruby -S t.rb
    ruby

### `-v`: Print Version; Set `$VERBOSE`

Options `-v` prints the Ruby version and sets global variable `$VERBOSE`:

    $ ruby -e 'p $VERBOSE'
    false
    $ ruby -v -e 'p $VERBOSE'
    ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [x64-mingw-ucrt]
    true

### `-w`: Synonym for `-W1`

Option `-w` (lowercase letter) is equivalent to option `-W1` (uppercase letter).

### `-W`: Set Warning Policy

Any Ruby code can create a warning message by calling method `Kernel#warn`; methods in the Ruby core and standard libraries can also create warning messages. Such a message may be printed on `$stderr` (or not, depending on certain settings).

Option `-W` helps determine whether a particular warning message will be written, by setting the initial value of global variable `$-W`:

- `-W0`: Sets `$-W` to `0` (silent; no warnings).

- `-W1`: Sets `$-W` to `1` (moderate verbosity).

- `-W2`: Sets `$-W` to `2` (high verbosity).

- `-W`: Same as `-W2` (high verbosity).

- Option not given: Same as `-W1` (moderate verbosity).

The value of `$-W`, in turn, determines which warning messages (if any) are to be printed to `$stdout` (see `Kernel#warn`):

    $ ruby -W1 -e 'p $foo'
    nil
    $ ruby -W2 -e 'p $foo'
    -e:1: warning: global variable '$foo' not initialized
    nil

Ruby code may also define warnings for certain categories; these are the default settings for the defined categories:

    Warning[:experimental] # => true
    Warning[:deprecated]   # => false
    Warning[:performance]  # => false

They may also be set:

    Warning[:experimental] = false
    Warning[:deprecated]   = true
    Warning[:performance]  = true

You can suppress a category by prefixing `no-` to the category name:

    $ ruby -W:no-experimental -e 'p IO::Buffer.new'
    #<IO::Buffer>

### `-x`: Execute Ruby Code Found in Text

Option `-x` executes a Ruby program whose code is embedded in other, non-code, text:

The ruby code:

- Begins after the first line beginning with `'#!` and containing string `'ruby'`.

- Ends before any one of:

  - End-of-file.

  - A line consisting of `'__END__'`,

  - Character `Ctrl-D` or `Ctrl-Z`.

Example:

    $ cat t.txt
    Leading garbage.
    #!ruby
    puts File.basename(Dir.pwd)
    __END__
    Trailing garbage.

    $ ruby -x t.txt
    ruby

The optional argument specifies the directory where the text file is to be found; the Ruby code is executed in that directory:

    $ cp t.txt /tmp/
    $ ruby -x/tmp t.txt
    tmp
    $

If an argument is given, it must immediately follow the option (no intervening whitespace or equal-sign character `'='`).

### `--backtrace-limit`: Set Backtrace Limit

Option `--backtrace-limit` sets a limit on the number of entries to be displayed in a backtrace.

See `Thread::Backtrace.limit`.

### `--copyright`: Print Ruby Copyright

Option `--copyright` prints a copyright message:

    $ ruby --copyright
    ruby - Copyright (C) 1993-2024 Yukihiro Matsumoto

### `--debug`: Alias for `-d`

Option `--debug` is an alias for option -d.

### `--disable`: Disable Features

Option `--disable` specifies features to be disabled; the argument is a comma-separated list of the features to be disabled:

    ruby --disable=gems,rubyopt t.rb

The supported features:

- `gems`: Rubygems (default: enabled).

- did_you_mean: `did_you_mean` (default: enabled).

- `rubyopt`: `RUBYOPT` environment variable (default: enabled).

- `frozen-string-literal`: Freeze all string literals (default: disabled).

- `jit`: JIT compiler (default: disabled).

See also option –enable.

### `--dump`: Dump Items

Option `--dump` specifies items to be dumped; the argument is a comma-separated list of the items.

Some of the argument values cause the command to behave as if a different option was given:

- `--dump=copyright`: Same as option –copyright.

- `--dump=help`: Same as option –help.

- `--dump=syntax`: Same as option -c.

- `--dump=usage`: Same as option -h.

- `--dump=version`: Same as option –version.

For other argument values and examples, see Option –dump.

### `--enable`: Enable Features

Option `--enable` specifies features to be enabled; the argument is a comma-separated list of the features to be enabled.

    ruby --enable=gems,rubyopt t.rb

For the features, see option –disable.

### `--encoding`: Alias for `-E`.

Option `--encoding` is an alias for option -E.

### `--external-encoding`: Set Default External Encoding

Option `--external-encoding` sets the default external encoding for the invoked Ruby program; for values of `encoding`, see Encoding: Names and Aliases.

    $ ruby -e 'puts Encoding::default_external'
    UTF-8
    $ ruby --external-encoding=cesu-8 -e 'puts Encoding::default_external'
    CESU-8

### `--help`: Print Help Message

Option `--help` prints a long help message.

Arguments and additional options are ignored.

For a shorter help message, use option `-h`.

### `--internal-encoding`: Set Default Internal Encoding

Option `--internal-encoding` sets the default internal encoding for the invoked Ruby program; for values of `encoding`, see Encoding: Names and Aliases.

    $ ruby -e 'puts Encoding::default_internal.nil?'
    true
    $ ruby --internal-encoding=cesu-8 -e 'puts Encoding::default_internal'
    CESU-8

### `--jit`

Option `--jit` is an alias for option `--yjit`, which enables YJIT; see additional YJIT options in the YJIT documentation.

### `--verbose`: Set `$VERBOSE`

Option `--verbose` sets global variable `$VERBOSE` to `true` and disables input from `$stdin`.

### `--version`: Print Ruby Version

Option `--version` prints the version of the Ruby interpreter, then exits.