ruby/doc/command_line/environment.md

Environment

Certain command-line options affect the execution environment of the invoked Ruby program.

About the Examples

The 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."'

Option -C

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.

Option -I

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.

Option -r

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.

Option -0

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 the argument is 0, the input record separator is ''; see {Special Line Separator Values}[rdoc-ref:IO@Special+Line+Separator+Values].
• If the argument is in range (1..0377), it becomes the character value of the input record separator $/.
• Otherwise, 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

The option may not be separated from its argument by whitespace.

Option -d

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 (or --debug) sets it to true:

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

Option '-w'

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

Option -W

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>