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53 lines
1.3 KiB
Markdown
53 lines
1.3 KiB
Markdown
# Override Output Field Separator
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Have you ever seen `$,` as a specific piece of syntax before? I've never
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actually seen any Ruby code that uses this in the wild. It's called the _output
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field separator_. By default it is `nil`. Like other keywords prefixed with `$`
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it is a global variable.
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It can be used to control what gets used by default as a separator in variety of
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contexts, like when calling `#join` without any argument.
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```ruby
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> [1,2,3].join
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=> "123"
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> $,
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=> nil
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> $, = '~'
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=> "~"
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> [1,2,3].join
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=> "1~2~3"
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```
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It is also what gets used when calling `print` with multiple arguments:
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```ruby
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> $, = ' |v| '
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=> " |v| "
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> print "hello", "world"
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hello |v| world=> nil
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> $, = "\t"
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=> "\t"
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> print "hello", "world"
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hello world=> nil
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```
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This seems pretty esoteric so far, but might be useful in a one-liner where
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we're doing something like parsing data from a CSV:
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```ruby
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# awk-style: pull fields 1 and 3 from a CSV, emit them tab-separated
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ruby -F, -ane 'BEGIN { $, = "\t"; $\ = "\n" }; print $F[0], $F[2]' data.csv
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```
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My attention was originally drawn to `$,` by a [post from Chris
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Oliver](https://lnkd.in/p/g6YH5KvQ) which showed this method definition from
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Rails source:
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```ruby
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def safe_join(array, sep = $,)
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```
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Note that this is [now
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deprecated](https://docs.ruby-lang.org/en/master/language/globals_md.html#deprecated).
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