72 lines
2.3 KiB
Markdown
72 lines
2.3 KiB
Markdown
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# Input and output flags
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In one-liners the `*input*` value may come in handy. It contains the input read
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from stdin as EDN by default. If you want to read in text, use the `-i` flag,
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which binds `*input*` to a lazy seq of lines of text. If you want to read
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multiple EDN values, use the `-I` flag. The `-o` option prints the result as
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lines of text. The `-O` option prints the result as lines of EDN values.
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> **Note:** `*input*` is only available in the `user` namespace, on other namespaces use `*in*`.
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The following table illustrates the combination of options for commands of the form
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echo "{{Input}}" | bb {{Input flags}} {{Output flags}} "*input*"
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| Input | Input flags | Output flag | `*input*` | Output |
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|----------------|-------------|-------------|---------------|----------|
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| `{:a 1}` <br> `{:a 2}` | | | `{:a 1}` | `{:a 1}` |
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| hello <br> bye | `-i` | | `("hello" "bye")` | `("hello" "bye")` |
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| hello <br> bye | `-i` | `-o` | `("hello" "bye")` | hello <br> bye |
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| `{:a 1}` <br> `{:a 2}` | `-I` | | `({:a 1} {:a 2})` | `({:a 1} {:a 2})` |
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| `{:a 1}` <br> `{:a 2}` | `-I` | `-O` | `({:a 1} {:a 2})` | `{:a 1}` <br> `{:a 2}` |
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When combined with the `--stream` option, the expression is executed for each value in the input:
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``` clojure
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$ echo '{:a 1} {:a 2}' | bb --stream '*input*'
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{:a 1}
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{:a 2}
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```
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When writing Clojure scripts that should be fully portable with the JVM, it is
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not recommended to use in- and output flags and `*input*` since those are not
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available in standard Clojure. Here is how you can rewrite:
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## EDN input
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Reading a single EDN value from stdin:
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``` clojure
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(ns script
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(:require [clojure.edn :as edn]))
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(edn/read *in*)
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```
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Reading multiple EDN values from stdin (the `-I` flag):
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``` clojure
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(ns script
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(:require [clojure.edn :as edn]
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[clojure.java.io :as io]))
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(let [reader (java.io.PushbackReader. (io/reader *in*))]
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(take-while #(not (identical? ::eof %)) (repeatedly #(edn/read {:eof ::eof} reader))))
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```
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## Text input
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Reading text from stdin can be done with `(slurp *in*)`. To get a lazy seq of
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lines (the `-i` flag), you can use:
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``` clojure
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(ns script
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(:require [clojure.java.io :as io]))
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(line-seq (io/reader *in*))
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```
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## Output
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To print to stdout, use `println` for text and `prn` for EDN values.
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