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bash/secret-handshake/README.md

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+# Secret Handshake
+
+> There are 10 types of people in the world: Those who understand
+> binary, and those who don't.
+
+You and your fellow cohort of those in the "know" when it comes to
+binary decide to come up with a secret "handshake".
+
+```text
+1 = wink
+10 = double blink
+100 = close your eyes
+1000 = jump
+
+
+10000 = Reverse the order of the operations in the secret handshake.
+```
+
+Given a decimal number, convert it to the appropriate sequence of events for a secret handshake.
+
+Here's a couple of examples:
+
+Given the input 3, the function would return the array
+["wink", "double blink"] because 3 is 11 in binary.
+
+Given the input 19, the function would return the array
+["double blink", "wink"] because 19 is 10011 in binary.
+Notice that the addition of 16 (10000 in binary)
+has caused the array to be reversed.
+
+
+Run the tests with:
+
+```bash
+bats secret_handshake_test.sh
+```
+
+After the first test(s) pass, continue by commenting out or removing the
+`[[ $BATS_RUN_SKIPPED == true ]] || skip` 
+annotations prepending other tests.
+
+To run all tests, including the ones with `skip` annotations, run:
+
+```bash
+BATS_RUN_SKIPPED=true bats secret_handshake_test.sh
+```
+
+## Source
+
+Bert, in Mary Poppins [http://www.imdb.com/title/tt0058331/quotes/qt0437047](http://www.imdb.com/title/tt0058331/quotes/qt0437047)
+
+
+## External utilities
+`Bash` is a language to write "scripts" -- programs that can call
+external tools, such as
+[`sed`](https://www.gnu.org/software/sed/),
+[`awk`](https://www.gnu.org/software/gawk/),
+[`date`](https://www.gnu.org/software/coreutils/manual/html_node/date-invocation.html)
+and even programs written in other programming languages, 
+like [`Python`](https://www.python.org/).
+This track does not restrict the usage of these utilities, and as long
+as your solution is portable between systems and does not require
+installation of third party applications, feel free to use them to solve
+the exercise.
+
+For an extra challenge, if you would like to have a better understanding
+of the language, try to re-implement the solution in pure `Bash`,
+without using any external tools. Note that there are some types of
+problems that bash cannot solve, such as performing floating point
+arithmetic and manipulating dates: for those, you must call out to an
+external tool.
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others
+have completed the exercise.

bash/secret-handshake/secret_handshake.sh

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+#!/usr/bin/env bash
+
+num=$1
+
+strings=(
+    "wink"
+    "double blink"
+    "close your eyes"
+    "jump"
+)
+reverse=n
+result=()
+
+(( $num & 2#10000 )) && reverse=y
+
+# get matching bits
+for (( i=0 ; i<4 ; ++i )); do
+    (( $num & 1<<$i )) && result+=( "${strings[$i]}" )
+done
+# output in normal or reverse order
+for (( i=0 ; i<${#result[@]} ; ++i)) ; do
+    [[ $reverse == n ]] && echo -n "$sep${result[i]}" || echo -n "$sep${result[~i]}"
+    sep=","
+done
+echo
+exit 0