Conch is actually two libraries. The first, me.raynes.conch.low-level
is a simple low-level
interface to the Java process APIs. The second and more interesting library is
an interface to low-level inspired by the Python
sh library.
The general idea is to be able to call programs just like you would call Clojure functions. See Usage for examples.
This library is the continuation of Raynes/conch. Sadly Raynes passed away in 2016 so the clj-commons clojure organisation has taken over maintenance of this excellent library.
With Leiningen:
First of all, let's require
a few things.
user> (require '[me.raynes.conch :refer [programs with-programs let-programs] :as sh])
nil
Let's call a program. What should we call? Let's call echo
, because I
obviously like to hear myself talk.
user> (programs echo)
#'user/echo
user> (echo "Hi!")
"Hi!\n"
Cool! programs
is a simple macro that takes a number of symbols and creates
functions that calls programs on the PATH with those names. echo
is now just a
normal function defined with defn
just like any other.
with-programs
and let-programs
are lexical and specialized versions of
programs
. with-programs
is exactly the same as programs
, only it defines
functions lexically:
user> (with-programs [ls] (ls))
"#README.md#\nREADME.md\nclasses\ndocs\nfoo.py\nlib\nlol\npom.xml\npom.xml.asc\nproject.clj\nsrc\ntarget\ntest\ntestfile\n"
user> ls
CompilerException java.lang.RuntimeException: Unable to resolve symbol: ls in
this context, compiling:(NO_SOURCE_PATH:1)
let-programs
is similar, but is useful for when you want to specify a path to
a program that is not on the PATH:
user> (let-programs [echo "/bin/echo"] (echo "hi!"))
"hi!\n"
Bad example since echo
is on the path, but if it wasn't there already it
still would have worked. I promise.
You can pass input to a program easily:
user> (programs cat)
#'user/cat
user> (cat {:in "hi"})
"hi"
user> (cat {:in ["hi" "there"]})
"hi\nthere\n"
user> (cat {:in (java.io.StringReader. "hi")})
"hi"
:in
is handled by a protocol and can thus be extended to support other data.
So, going back to our ls
example. Of course, ls
gives us a bunch of
lines. In a lot of cases, we're going to want to process lines individually. We
can do that by telling conch that we want a lazy seq of lines instead of a
monolithic string:
user> (ls {:seq true})
("#README.md#" "README.md" "classes" "docs" "foo.py" "lib" "lol" "pom.xml"
"pom.xml.asc" "project.clj" "src" "target" "test" "testfile")
We can also redirect output to other places.
user> (let [writer (java.io.StringWriter.)] (echo "foo" {:out writer}) (str writer))
"foo\n"
user> (echo "foo" {:out (java.io.File. "conch")})
nil
user> (slurp "conch")
"foo\n"
And if that wasn't cool enough for you, :out
is handled by a protocol and thus
can be extended.
Need the exit code and stuff? Sure:
user> (echo "foo" {:verbose true})
{:proc {:out ("foo\n"), :in #<ProcessPipeOutputStream
java.lang.UNIXProcess$ProcessPipeOutputStream@19c12ee7>, :err (), :process
#<UNIXProcess java.lang.UNIXProcess@2bfabe2a>}, :exit-code
#<core$future_call$reify__6110@5adacdf4: 0>, :stdout "foo\n", :stderr ""}
user> (sleep "5")
... yawn ...
Tired of waiting for that pesky process to exit? Make it go away!
user> (sleep "5" {:timeout 2000})
... two seconds later ...
ExceptionInfo Program returned non-zero exit code :timeout clojure.core/ex-info (core.clj:4227)
Much better.
Conch can handle exit codes pretty well. You can make it do pretty much whatever you want in failure scenarios.
By default, conch throws ExceptionInfo
exceptions for non-zero exit codes, as
demonstrated here:
user> (ls "-2")
ExceptionInfo Program returned non-zero exit code 1 clojure.core/ex-info
(core.clj:4227)
This exception's data is the same result you'd get by passing the :verbose
option:
user> (ex-data *e)
{:proc {:out (), :in #<ProcessPipeOutputStream java.lang.UNIXProcess$ProcessPipeOutputStream@79bb65ee>, :err ("ls: illegal
option -- 2\nusage: ls [-ABCFGHLOPRSTUWabcdefghiklmnopqrstuwx1] [file ...]\n"), :process #<UNIXProcess java.lang.UNIXProcess@1172897f>}, :exit-code #<core$future_call$reify__6110@76a0f9cb: 1>, :stdout "", :stderr "ls: illegal option -- 2\nusage: ls [-ABCFGHLOPRSTUWabcdefghiklmnopqrstuwx1] [file ...]\n"}
You can control this behavior in two ways. The first way is to set
me.raynes.conch/*throw*
to false
:
user> (binding [sh/*throw* false] (ls "-2"))
""
You can also just override whatever *throw*
is with the :throw
argument to
the functions themselves:
user> (ls "-2" {:throw false})
""
You can pipe the output of one program as the input to another about how you'd expect:
user> (programs grep ps)
#'user/ps
user> (grep "ssh" {:in (ps "-e" {:seq true})})
" 4554 ?? 0:00.77 /usr/bin/ssh-agent -l\n"
These functions also look for a lazy seq arg, so you can get rid of the explicit
:in
part.
user> (programs grep ps)
#'user/ps
user> (grep "ssh" (ps "-e" {:seq true}))
" 4554 ?? 0:00.77 /usr/bin/ssh-agent -l\n"
Conch gets rid of some ugly edge-cases by always reading process output immediately when it becomes available. It buffers this data into a queue that you consume however you want. This is how returning lazy seqs work. Keep in mind that if you don't consume data, it is being held in memory.
You can change how conch buffers data using the :buffer
key.
user> (ls {:seq true :buffer 5})
("#READ" "ME.md" "#\nREA" "DME.m" "d\ncla" "sses\n" "conch" "\ndocs" "\nfoo." "py\nli" "b\nlol" "\npom." "xml\np" "om.xm" "l.asc" "\nproj" "ect.c" "lj\nsr" "c\ntar" "get\nt" "est\nt" "estfi" "le\n")
user> (ls {:seq true :buffer :none})
(\# \R \E \A \D \M \E \. \m \d \# \newline \R \E \A \D \M \E \. \m \d \newline
\c \l \a \s \s \e \s \newline \c \o \n \c \h \newline \d \o \c \s \newline \f \o
\o \. \p \y \newline \l \i \b \newline \l \o \l \newline \p \o \m \. \x \m \l
\newline \p \o \m \. \x \m \l \. \a \s \c \newline \p \r \o \j \e \c \t \. \c \l
\j \newline \s \r \c \newline \t \a \r \g \e \t \newline \t \e \s \t \newline \t
\e \s \t \f \i \l \e \newline)
Another nice thing gained by the way conch consumes data is that it is able to kill a process after a timeout and keep whatever data it has already consumed.
PTY stuff seems like it'd be a lot of work and would involve non-Clojure stuff. If you need a PTY for output, I suggest wrapping your programs in 'unbuffer' from the expect package. It usually does the trick for unbuffering program output by making it think a terminal is talking to it.
You might run into an issue where your program finishes after using conch but does not exit. Conch uses futures under the hood which spin off threads that stick around for a minute or so after everything else is done. This is an unfortunate side effect, but futures are necessary to conch's functionality so I'm not sure there is much I can do about it.
You can work around this by adding a (System/exit 0)
call to the end of your program.
The low-level API is available in a separate package:
(use '[me.raynes.conch.low-level :as sh])
It is pretty simple. You spin off a process with proc
.
user=> (def p (sh/proc "cat"))
#'user/p
user=> p
{:out #<BufferedInputStream java.io.BufferedInputStream@5809fdee>, :in #<BufferedOutputStream java.io.BufferedOutputStream@5ebbfa5c>, :err #<DeferredCloseInputStream java.lang.UNIXProcess$DeferredCloseInputStream@58e5f46e>, :process #<UNIXProcess java.lang.UNIXProcess@18f42160>}
When you create a process with proc
, you get back a map containing the
keys :out
, :err
, :in
, and :process
.
:out
is the process's stdout.:err
is the process's stderr.:in
is the process's stdin.:process
is the process object itself.Conch is more flexible than clojure.java.shell
because you have direct
access to all of the streams and the process object itself.
So, now we have a cat process. This is a unix tool. If you
run cat
with no arguments, it echos whatever you type in. This makes it
perfect for testing input and output.
Conch defines a few utility functions for streaming output and feeding input. Since we want to make sure that our input is going to the right place, let's set up a way to see the output of our process in realtime:
user=> (future (sh/stream-to-out p :out))
#<core$future_call$reify__5684@77b5c22f: :pending>
The stream-to-out
function takes a process and either :out
or :err
and streams that to System/out
. In this case, it has the effect of printing
everything we pipe into our cat process, since our cat process just
outputs whatever we input.
user=> (sh/feed-from-string p "foo\n")
nil
foo
The feed-from-string
function just feeds a string to the process. It
automatically flushes (which is why this prints immediately) but you can
stop it from doing that by passing :flush false
.
I think our cat process has lived long enough. Let's kill it and get its
exit code. We can use the exit-code
function to get the exit code.
However, since exit-code
stops the thread and waits for the process to
terminate, we should run it in a future until we actually destroy the
process.
user=> (def exit (future (sh/exit-code p)))
#'user/exit
Now let's kill. R.I.P process.
user=> (sh/destroy p)
nil
And the exit code, which we should be able to obtain now that the process has been terminated:
user=> @exit
0
Awesome! Let's go back to proc
and see what else we can do with it. We
can pass multiple strings to proc
. The first string will be considered
the executable and the rest of them the arguments to that executable.
user=> (sh/proc "ls" "-l")
{:out #<BufferedInputStream java.io.BufferedInputStream@7fb6634c>, :in #<BufferedOutputStream java.io.BufferedOutputStream@1f315415>, :err #<DeferredCloseInputStream java.lang.UNIXProcess$DeferredCloseInputStream@5f873eb2>, :process #<UNIXProcess java.lang.UNIXProcess@2825491d>}
(require '[me.raynes.conch.low-level :as sh])
Here is an easy way to get the output of a one-off process like this as a string:
user=> (sh/stream-to-string (sh/proc "ls" "-l") :out)
"total 16\n-rw-r--r-- 1 anthony staff 2545 Jan 24 16:37 README.md\ndrwxr-xr-x 2 anthony staff 68 Jan 19 19:23 classes\ndrwxr-xr-x 3 anthony staff 102 Jan 19 19:23 lib\n-rw-r--r-- 1 anthony staff 120 Jan 20 14:45 project.clj\ndrwxr-xr-x 3 anthony staff 102 Jan 20 14:45 src\ndrwxr-xr-x 3 anthony staff 102 Jan 19 16:36 test\n"
Let's print that for readability:
user=> (print (sh/stream-to-string (sh/proc "ls" "-l") :out))
total 16
-rw-r--r-- 1 anthony staff 2545 Jan 24 16:37 README.md
drwxr-xr-x 2 anthony staff 68 Jan 19 19:23 classes
drwxr-xr-x 3 anthony staff 102 Jan 19 19:23 lib
-rw-r--r-- 1 anthony staff 120 Jan 20 14:45 project.clj
drwxr-xr-x 3 anthony staff 102 Jan 20 14:45 src
drwxr-xr-x 3 anthony staff 102 Jan 19 16:36 test
nil
So, that's the ls
of the current directory. I ran this REPL in the
conch project directory. We can, of course, pass a directory to ls
to
get it to list the files in that directory, but that isn't any fun. We
can pass a directory to proc
itself and it'll run in the context of
that directory.
user=> (print (sh/stream-to-string (sh/proc "ls" "-l" :dir "lib/") :out))
total 6624
-rw-r--r-- 1 anthony staff 3390414 Jan 19 19:23 clojure-1.3.0.jar
nil
You can also pass a java.io.File
or anything that can be passed to
clojure.java.io/file
.
We can also set environment variables:
user=> (print (sh/stream-to-string (sh/proc "env" :env {"FOO" "bar"}) :out))
FOO=bar
nil
The map passed to :env
completely replaces any other environment
variables that were in place.
Finally, there a couple of low-level functions for streaming from and
feeding to a process. They are stream-to
and feed-from
. These
functions are what the utility functions are built off of, and you can
probably use them to stream to and feed from your own special places.
You might want to fire off a program that listens for input until EOF.
In these cases, you can feed it data for as long as you want and just
tell it when you are done. Let's use pygmentize
as an example:
user=> (def proc (sh/proc "pygmentize" "-fhtml" "-lclojure"))
#'user/proc
user=> (sh/feed-from-string proc "(+ 3 3)")
nil
user=> (sh/done proc)
nil
user=> (sh/stream-to-string proc :out)
"<div class=\"highlight\"><pre><span class=\"p\">(</span><span class=\"nb\">+ </span><span class=\"mi\">3</span> <span class=\"mi\">3</span><span class=\"p\">)</span>\n</pre></div>\n"
When we call done
, it closes the process's output stream which is
like sending EOF. The process processes its input and then puts it on
its input stream where we read it with stream-to-string
.
All of conch's streaming and feeding functions (including the lower
level ones) pass all of their keyword options to clojure.java.io/copy
.
It can take an :encoding
and :buffer-size
option. Guess what they
do.
You might notice that the map that proc
returns is mapped like so:
:in
-> output stream:out
-> input streamI did this because swapping them feels counterintuitive. The output
stream is what you put :in
to and the input stream is what you pull
:out
from.
Copyright (C) 2012 Anthony Grimes
Distributed under the Eclipse Public License, the same as Clojure.
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