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A LISP that runs wherever Bash is
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Fleck is a Clojure-like LISP that runs wherever Bash is.

Fleck screencast

Get it

curl -s > flk && chmod 755 flk

Examples | Reference | FAQ | make-a-lisp


$ echo '(println "Hello world!") (println "Hostname:" (sh* "hostname")))' > example.clj
$ ./flk example.clj
Hello world!
Hostname: diziet


Now you can use a humble LISP to do Bash things. Bash as a scripting language has many edges, but it is everywhere. Fleck attempts to round off the edges.

Fleck runs on Bash 4 and higher.


Almost all of this code is from the make-a-LISP project. All I've done is put together a simple Makefile to package it up into an easily deployable single-file bash script.


A list of variables, macros and functions that are present in Fleck.


This is the set of built-ins from the make-a-lisp project. These more or less work but are generally more limited in functionality than their Clojure equivalents. For example the addition function (+) can only add two integers at a time.

def! | defmacro! | if | do | fn* | try* | sh* | let* | quote | quasiquote | macroexpand | type | = | throw | nil? | true? | false? | string? | symbol | symbol? | keyword | keyword? | number? | fn? | macro? | pr-str | str | prn | println | readline | read-string | slurp | < | <= | > | >= | + | - | * | / | time-ms | list | list? | vector | vector? | hash-map | map? | assoc | dissoc | get | contains? | keys | vals | sequential? | cons | concat | nth | first | rest | empty? | count | apply | map | conj | seq | with-meta | meta | atom | atom? | deref | reset! | swap!

  • *ARGV* - list of arguments passed on the command line.


These are wrappers around the limited make-a-lisp versions and are much more limited than the Clojure equivalents.

let | when | def | fn | defn

Mal extras

These functions are pulled from a selection of mal/lib/*.mal.

partial | inc | dec | zero | identity | reduce | foldr

Fleck extras

These functions are hand crafted Fleck specials designed to make common shell scripting tasks easier.

  • (str-replace STRING FIND REPLACE) - Replace all occurrences of the string FIND in STRING with the string REPLACE.
  • (str-split STRING SPLIT-CHARACTER) - Split STRING into a list of strings on the single characters SPLIT-CHARACTER.
  • (dc OPERATOR ARRAY-OF-NUMBERS) - Wraps the dc command to do decimal math. E.g. (dc '+ [1 2 3]) yeilds 6.
  • (env [KEY] [VALUE]) - Returns a hash-map of environment variables. Returns the value of KEY if present. Sets the value of KEY to VAL if the latter is present.


  • (sh* COMMAND) - Run arbitrary bash strings and return the stdout result.
  • (env [KEY] [VALUE]) - See above section.

For examples of writing your own Fleck functions in Bash see src/ Functions should set the special return value r and use Fleck type casting functions like _string to wrap the result in a reference. Internal Fleck functions such as _string automatically do this and can be used bare. Use _fref to make your function available to the Fleck namespace e.g. _fref "my-bash-function" _my_bash_function.


You can make a pure bash script from your Fleck script by bundling your script and Fleck together into a new script.

Say you have a Fleck script called wow.clj, you can bundle it as follows:

make DEST=wow INSERT=./wow.clj NOREPL=1

This will produce a new standalone script called wow with Fleck + wow.clj bundled together.

When you run wow the embedded wow.clj will be run by the embedded Fleck.


Think of this as homoiconic Bash rather than Clojure, and code as if you're in Bash.

Will my favourite piece of Clojure run in this?

No, it's bash.

Some subset of Clojure-like code will run. See the documentation and examples.

How do I access command line arguments?

Use the special global list *ARGV*.

How do I access and modify environment variables?

Check the (env) function above. See also examples/environment-variables.clj.

How can I execute a one-liner of Fleck code?

Either of these methods will work:

flk <<< '(println "hi")'
echo '(println "hi")' | flk

Why can't I add more than 2 numbers together?

It's bash. Try the dc function: (dc '+ [1 2 3 4])

Where are the floating point numbers?

It's bash. Try the dc function for decimals: (dc '* [8.2 3.5])

Note that dc's divide seems to only output integers. ¯\(ツ)

How do I cast a string to a number?

Try (read-str "42") but also Bash doesn't care and (+ "1" 1) will yeild 2.

Why can't I iterate on a string?

Try (seq "somestring").

How do I do destructuring?

You can't.

Can I use anything as a hash-map key?

Seems unlikely. Better stick to strings.

This is even slower than Python!


PS That is not actually a question.

Why is it called Fleck?

At 36k and running on any machine with Bash 4, the name seemed appropriate.


    n. A tiny mark or spot.
    n. A small bit or flake.
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