jq is better for json parsing

rust-lang#423 (comment) was having problems installing. (I think their python3 install was having a problem parsing json?) Having an install fail just because it was unable to locate the version number seems like "my kingdom for a horseshoe nail" now that the version is relatively stable. (Its good to have a single point of truth, but) we could have an emergency version number of "3.0.0" in this file rather than have the install fail because rust and rustlings does not depend on python for to function.

Having this rustlings install depend on bash that depends on python seems like "extra steps" that could be avoided. The pure shell version also works with some other shells such as dash.

install.sh

@@ -40,15 +40,26 @@ then
 elif [ -x "$(command -v python2)" ]
 then
     PY="$(command -v python2)"
+elif [ -x "$(command -v jq)" ]
+then
+    PY="" # we will ignore python and try to use jq
+    JQ="$(command -v jq)" #jq is much faster than python for json parsing
 else
-    echo "ERROR: No working python installation was found"
-    echo "Please install python and add it to the PATH variable"
-    exit 1
+    echo "WARNING: No working python installation was found; trying jq"
+    #echo "Please install python and add it to the PATH variable"
+    #exit 1
+fi
+
+# install jq for faster and more efficient json parsing
+if [ -x "$(command -v brew)" ] && uname -a|grep -q Darwin;
+then # probably OSX
+    command -v jq 1>/dev/null|| $(command -v brew ) install jq
+    JQ="$(command -v jq)" #jq is much faster than python for json parsing
 fi
 
 # Function that compares two versions strings v1 and v2 given in arguments (e.g 1.31 and 1.33.0).
 # Returns 1 if v1 > v2, 0 if v1 == v2, 2 if v1 < v2.
-function vercomp() {
+vercomp() {
     if [[ $1 == $2 ]]
     then
         return 0
@@ -102,7 +113,36 @@ Path=${1:-rustlings/}
 echo "Cloning Rustlings at $Path..."
 git clone -q https://github.com/rust-lang/rustlings $Path
 
-Version=$(curl -s https://api.github.com/repos/rust-lang/rustlings/releases/latest | ${PY} -c "import json,sys;obj=json.load(sys.stdin);print(obj['tag_name']);")
+# function to locate the version number from the latest releases JSON
+locate_version(){
+  if [ -x "$JQ" ]; then
+    curl -s https://api.github.com/repos/rust-lang/rustlings/releases/latest | $JQ -r .tag_name
+  elif [ -x "$PY" ]; then
+    curl -s https://api.github.com/repos/rust-lang/rustlings/releases/latest | ${PY} -c "import json,sys;obj=json.load(sys.stdin);print(obj['tag_name']);"
+  else # try to use BASH to locate the version number in the json
+    #if [ ! -f "/tmp/rustlings_latest.json" ]; then
+    #  curl -s https://api.github.com/repos/rust-lang/rustlings/releases/latest > /tmp/rustlings_latest.json
+    #  #curl -s https://api.github.com/repos/rust-lang/rustlings/releases/latest|grep tag_name|awk '{print $NF}'|tr -d '"'|tr -d ','
+    #fi
+    #if [ -f "/tmp/rustlings_latest.json" ]; then #  the advantage of writing to a temp file is that we can error if the network, (or curl) fail.
+    #  ## Writing to a temp file so that my tests don't hammer the github api
+    #  #grep tag_name /tmp/rustlings_latest.json|awk '{print $NF}'|tr -d '"'|tr -d ','
+    #  # the above line is faster but requires awk and tr 
+    #  VER=$(grep tag_name /tmp/rustlings_latest.json)
+      VER=$(curl -s https://api.github.com/repos/rust-lang/rustlings/releases/latest|grep tag_name)
+      VER=${VER%\"*} # shadowing
+      VER=${VER##*\"}
+    if [ "$VER" ];then # we can do this in memory, rather than writing to /tmp/
+      echo $VER
+    else
+      # echo 3.0.0 # we could fall back to a default version and change this to a WARNING?
+      echo "ERROR: unable to parse json using either jq or python" >&2
+      exit 1
+    fi
+  fi
+}
+
+Version="$(locate_version)"
 CargoBin="${CARGO_HOME:-$HOME/.cargo}/bin"
 
 echo "Checking out version $Version..."