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How to read lines from stdin (*in*) in clojure
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Closed 2 years ago.
I´m building a CLI on Clojure that will receive a file called operations.txt that will have in every line an operation that I want to process. Let's say:
clojure -M -m project.process < operations.txt
Right now I have a simple repo with deps and when I don't add the < operator I can receive the file name as an argument, but once I added the operator the arguments returns nil.
Is there something I can do for this?
I don't have to much added to my project other the what is created with https://github.com/seancorfield/clj-new command.
Here is the code on the main file:
(defn -main
"I don't do a whole lot ... yet."
[& args]
(println args))
What I mean to receive in the arguments on this function is something similar that if I was using this:
cat < operations.txt
If you use < on the command line, then the contents of 'operations.txt' will be available not as an argument to -main, but as stdin, which you can access via *in*.
You can use read-line to read a single line, or wrap it in a BufferedReader and process it with doseq.
(doseq [line (line-seq (java.io.BufferedReader. *in*))]
(println line))
See more details at this question.
Related
I'd like to run an interactive CLI program from within Clojure (e.g., vim) and be able to interact with it.
In bash and other programming languages, I can do that with
vim > `tty`
I tried to do the same in Clojure:
(require '[clojure.java.shell :as shell])
(shell/sh "vim > `tty`")
but it just opens vim without giving me tty.
Background: I'm developing a Clojure CLI tool which parses emails and lets a user edit the parsed data before saving them on the disk. It works the following way:
Read a file with email content and parse it. Each email is stored as a separate file.
Show a user the parsed data and let the user edit the data in vim. Internally I create a temporary file with the parsed data, but I don't mind doing it another way if that would solve my issue.
After a user finished editing the parsed data (they might decide to keep it as it is) append the data to a file on a disk. So all parsed data are saved to the same file.
Go to 1st step if there are any files with emails left.
This code relies on Clojure Java interop to make use of Java's ProcessBuilder class.
(defn -main
[]
;use doseq instead of for because for is lazily evaluated
(doseq [i [1 2 3]]
;extract current directory from system variable
(let [file-name (str "test" i ".txt")
working-directory (trim-newline (:out (sh "printenv" "PWD")))]
(spit file-name "")
;this is where fun begins. We use ProcessBuilder to forward commands to terminal
;we pass a list of commands and their arguments to its constructor
(let [process-builder (java.lang.ProcessBuilder. (list "vim" (str working-directory "/" file-name)))
;inherit is a configuration constant
inherit (java.lang.ProcessBuilder$Redirect/INHERIT)]
;we configure input, output and error redirection
(.redirectOutput process-builder inherit)
(.redirectError process-builder inherit)
(.redirectInput process-builder inherit)
;waitFor used to block execution until vim is closed
(.waitFor (.start process-builder))
)
;additional processing here
)
)
;not necessary but script tends to hang for around 30 seconds at end of its execution
;so this command is used to terminate it instantly
(System/exit 0)
)
Is there a way to get a dump of all the source code I have entered into a repl session. I have created a bunch of functions using (defn ...) but did it 'on the fly' without entering them in a text file (IDE) first.
Is there a convenience way to get the source back out of the repl session?
I note that:
(dir user)
will give me a printed list of type:
user.proxy$java.lang.Object
so I can't appear to get that printed list into a Seq for mapping a function like 'source' over. And even if I could then:
(source my-defined-fn)
returns "source not found"...even though I personally entered it in to the repl session.
Any way of doing this? Thanks.
Sorry, but I suspect the answer is no :-/
The best you get is scrolling up in the repl buffer to where you defined it. The source function works by looking in the var's metadata for the file and line number where the functions code is (or was last time it was evaluated), opening the file, and printing the lines. It looks like this:
...
(when-let [filepath (:file (meta v))]
(when-let [strm (.getResourceAsStream (RT/baseLoader) filepath)]
(with-open [rdr (LineNumberReader. (InputStreamReader. strm))]
(dotimes [_ (dec (:line (meta v)))] (.readLine rdr))
...
Not including the full source in the metadata was done on purpose to save memory in the normal case, though it does make it less convenient here.
I'm writing a Brainf*** interpreter in Clojure. I want to pass a program in using stdin. However, I still need to read from stdin later for user input.
Currently, I'm doing this:
$ cat sample_programs/hello_world.bf | lein trampoline run
My Clojure code is only reading the first line though, using read-line:
(defn -main
"Read a BF program from stdin and evaluate it."
[]
;; FIXME: only reads the first line from stdin
(eval-program (read-line)))
How can I read all the lines in the file I've piped in? *in* seems to be an instance of java.io.Reader, but that only provides .read (one char), .readLine (one line) and read(char[] cbuf, int off, int len) (seems very low level).
It's simple enough to read all input data as a single string:
(defn -main []
(let [in (slurp *in*)]
(println in)))
This works fine if your file can fit in available memory; for reading large files lazily, see this answer.
you could get a lazy seq of lines from *in* like this:
(take-while identity (repeatedly #(.readLine *in*)))
or this:
(line-seq (java.io.BufferedReader. *in*))
which are functionally identical.
I am writing a text game in Clojure. I want the player to type lines at the console, and the game to respond on a line-by-line basis.
Research showed me that (read-line) is the way one is meant to get text lines from standard input in Clojure, but it is not working for me.
I am in a fresh Leiningen project, and I have added a :main clause to the project.clj pointing to the only source file:
(ns textgame.core)
(defn -main [& args]
(println "Entering -main")
; (flush) ;makes no difference if flush are commented out
(let [input (read-line)]
(println "ECHO:" input))
; (flush)
(println "Exiting -main"))
using lein run yields:
Entering -main
ECHO: nil
Exiting -main
In other words, there is no opportunity to enter text at the console for (read-line) to read.
How should I get Clojure to wait for characters and newline to be entered and return the corresponding string?
(I am using GNOME Terminal 2.32.1 on Linux Mint 11, Leiningen 1.6.1.1 on Java 1.6.0_26 Java HotSpot(TM) 64-Bit Server VM, Clojure version 1.2.1.)
Update: If I run lein repl, I can (println (read-line)), but not when I have a -main function and run using lein run.
Try "lein trampoline run". See http://groups.google.com/group/leiningen/browse_thread/thread/a07a7f10edb77c9b for more details also from https://github.com/technomancy/leiningen:
Q: I don't have access to stdin inside my project.
A: There's a problem in the library that Leiningen uses to spawn new processes that blocks access to console input. This means that functions like read-line will not work as expected in most contexts, though the repl task necessarily includes a workaround. You can also use the trampoline task to launch your project's JVM after Leiningen's has exited rather than launching it as a subprocess.
I have had similar problems and resorted to building a jar file and then running that.
lein uberjar
java -jar project-standalone.jar
It's a bit slower, though it got me unstuck. An answer that works from the repl would
be better
Wrap your read-line calls with the macro with-read-line-support which is now in ns swank.core [since swank-clojure 1.4+ I believe]:
(use 'swank.core)
(with-read-line-support
(println "a line from Emacs:" (read-line)))
Thanks to Tavis Judd for the fix.
You can use read and use a string as input.
Not sure about the lein aspects of the problem, but definitely in emacs it is impossible to make stdin work. However, if you want to get text from the user, you can easily do it using a JOptionPane like this code from my little tic-tac-toe program:
(defn get-input []
(let [input (JOptionPane/showInputDialog "Enter your next move (row/column)")]
(map #(Integer/valueOf %) (.split input "/"))))
How would you convert a clojure source file to YAML? I have used the clj-yaml library to do it in the interactive REPL, but I'd like to automate this, so I can pass in an input file and specify an output, ie:
clj2yaml input.clj > output.yml
As I understand it you need help to read and write the files?! See slurp and spit. For a real example of reading a YAML config file and parsing it with clj-yaml, see pswincom.gateway.config.
And here's an implementation of a simple clojure tool to do the convertion:
(ns sample
(:require [clj-yaml.core :as yaml]))
(->> (slurp (nth *command-line-args* 0))
read-string ; converts the file content to a clojure datastructure
yaml/generate-string
(spit (nth *command-line-args* 1)))
(On Windows) I can create a batch file called clj2yaml.bat to make it easy to use. It assumes the needed jar-files are located in the current directory. I'm just a novice when it comes to this kind of execution, so a better script is quite likely possible, but here it is:
java.exe -cp .\clojure-1.2.0.jar;.\clojure-contrib-1.2.0.jar;.\clj-yaml-0.3.0-20101010.033133-1.jar;.\snakeyaml-1.5.jar clojure.main sample.clj %*
I can now execute clj2yaml foo.clj foo.yaml to create the yaml file.
You already know how to code a clojure converter, you now just need to package it as a standalone application, and possibly create a sh script that just invokes your class.
As an alternative, here's a neat way to do it, if you're on a *nix environment:
#^:shebang '[
exec java -cp "$HOME/src/clj/clojure/clojure.jar" clojure.lang.Script "$0" -- "$#"
]
(your code here)