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0ea5c13bc6
* Fix WASM bullet/code indentation * Use `console` code highlighting where appropriate … which handles the prefix `$` correctly. * Migrate feature proposal template to MarkDown * Set language on code blocks
174 lines
4.1 KiB
Markdown
174 lines
4.1 KiB
Markdown
## Environment
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Certain command-line options affect the execution environment
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of the invoked Ruby program.
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### About the Examples
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The examples here use command-line option `-e`,
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which passes the Ruby code to be executed on the command line itself:
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```console
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$ ruby -e 'puts "Hello, World."'
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```
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### Option `-C`
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The argument to option `-C` specifies a working directory
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for the invoked Ruby program;
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does not change the working directory for the current process:
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```console
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$ basename `pwd`
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ruby
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$ ruby -C lib -e 'puts File.basename(Dir.pwd)'
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lib
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$ basename `pwd`
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ruby
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```
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Whitespace between the option and its argument may be omitted.
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### Option `-I`
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The argument to option `-I` specifies a directory
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to be added to the array in global variable `$LOAD_PATH`;
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the option may be given more than once:
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```console
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$ pushd /tmp
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$ ruby -e 'p $LOAD_PATH.size'
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8
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$ ruby -I my_lib -I some_lib -e 'p $LOAD_PATH.size'
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10
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$ ruby -I my_lib -I some_lib -e 'p $LOAD_PATH.take(2)'
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["/tmp/my_lib", "/tmp/some_lib"]
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$ popd
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```
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Whitespace between the option and its argument may be omitted.
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### Option `-r`
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The argument to option `-r` specifies a library to be required
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before executing the Ruby program;
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the option may be given more than once:
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```console
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$ ruby -e 'p defined?(JSON); p defined?(CSV)'
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nil
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nil
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$ ruby -r CSV -r JSON -e 'p defined?(JSON); p defined?(CSV)'
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"constant"
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"constant"
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```
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Whitespace between the option and its argument may be omitted.
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### Option `-0`
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Option `-0` defines the input record separator `$/`
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for the invoked Ruby program.
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The optional argument to the option must be octal digits,
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each in the range `0..7`;
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these digits are prefixed with digit `0` to form an octal value:
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- If no argument is given, the input record separator is `0x00`.
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- If the argument is `0`, the input record separator is `''`;
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see {Special Line Separator Values}[rdoc-ref:IO@Special+Line+Separator+Values].
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- If the argument is in range `(1..0377)`,
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it becomes the character value of the input record separator `$/`.
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- Otherwise, the input record separator is `nil`.
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Examples:
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```console
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$ ruby -0 -e 'p $/'
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"\x00"
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$ ruby -00 -e 'p $/'
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""
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$ ruby -012 -e 'p $/'
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"\n"
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$ ruby -015 -e 'p $/'
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"\r"
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$ ruby -0377 -e 'p $/'
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"\xFF"
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$ ruby -0400 -e 'p $/'
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nil
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```
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The option may not be separated from its argument by whitespace.
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### Option `-d`
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Some code in (or called by) the Ruby program may include statements or blocks
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conditioned by the global variable `$DEBUG` (e.g., `if $DEBUG`);
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these commonly write to `$stdout` or `$stderr`.
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The default value for `$DEBUG` is `false`;
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option `-d` (or `--debug`) sets it to `true`:
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```console
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$ ruby -e 'p $DEBUG'
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false
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$ ruby -d -e 'p $DEBUG'
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true
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```
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### Option '-w'
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Option `-w` (lowercase letter) is equivalent to option `-W1` (uppercase letter).
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### Option `-W`
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Any Ruby code can create a <i>warning message</i> by calling method Kernel#warn;
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methods in the Ruby core and standard libraries can also create warning messages.
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Such a message may be printed on `$stderr`
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(or not, depending on certain settings).
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Option `-W` helps determine whether a particular warning message
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will be written,
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by setting the initial value of global variable `$-W`:
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- `-W0`: Sets `$-W` to `0` (silent; no warnings).
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- `-W1`: Sets `$-W` to `1` (moderate verbosity).
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- `-W2`: Sets `$-W` to `2` (high verbosity).
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- `-W`: Same as `-W2` (high verbosity).
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- Option not given: Same as `-W1` (moderate verbosity).
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The value of `$-W`, in turn, determines which warning messages (if any)
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are to be printed to `$stdout` (see Kernel#warn):
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```console
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$ ruby -W1 -e 'p $foo'
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nil
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$ ruby -W2 -e 'p $foo'
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-e:1: warning: global variable '$foo' not initialized
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nil
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```
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Ruby code may also define warnings for certain categories;
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these are the default settings for the defined categories:
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```ruby
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Warning[:experimental] # => true
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Warning[:deprecated] # => false
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Warning[:performance] # => false
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```
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They may also be set:
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```ruby
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Warning[:experimental] = false
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Warning[:deprecated] = true
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Warning[:performance] = true
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```
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You can suppress a category by prefixing `no-` to the category name:
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```console
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$ ruby -W:no-experimental -e 'p IO::Buffer.new'
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#<IO::Buffer>
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```
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