From 3647703c4fd9079475c5ac5661c5b98f43ac2a27 Mon Sep 17 00:00:00 2001
From: Mark Allen <mrallen1@yahoo.com>
Date: Thu, 2 Feb 2017 18:08:09 -0600
Subject: Assert perl exists before builds (#170)

Perl 5 is required to compile Erlang from source. It's used (among other
things) to assemble BEAM opcodes, NIF jump tables and more. We now
assert perl exists on the PATH before we proceed to build Erlang or test
for Perl's version string.

We also now test for Java before we try to find its version. Java is not
required to compile Erlang though, so we don't output any warnings or
errors if its not found.
---
 kerl | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/kerl b/kerl
index a494256..11d6fe2 100755
--- a/kerl
+++ b/kerl
@@ -382,13 +382,35 @@ get_otp_version()
 
 get_perl_version()
 {
-    perl -v | grep version | sed $SED_OPT -e 's/.*v5\.([0-9]+)\.[0-9].*/\1/'
+    if assert_perl; then
+        perl -v | grep version | sed $SED_OPT -e 's/.*v5\.([0-9]+)\.[0-9].*/\1/'
+    else
+        echo "FATAL: I couldn't find perl which is required to compile Erlang."
+        exit 1
+    fi
+}
+
+assert_perl()
+{
+    perl_loc=$(which perl)
+    if [ -z "$perl_loc" ]; then
+        return 1
+    else
+        # 0 to bash is "true" because of Unix exit code conventions
+        return 0
+    fi
 }
 
 get_javac_version()
 {
-    javaout=$(javac -version 2>&1)
-    echo "$javaout" | cut -d' ' -f2 | cut -d'.' -f2
+    java_loc=$(which javac)
+    if [ -z "$java_loc" ]; then
+        # Java's not installed, so just return 0
+        0
+    else
+        javaout=$(javac -version 2>&1)
+        echo "$javaout" | cut -d' ' -f2 | cut -d'.' -f2
+    fi
 }
 
 show_configuration_warnings()
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