Prefer command -v <cmd> to which <cmd> (heroku#1716)

* Prefer `command -v <cmd>` to `which <cmd>`


Mentioned in heroku#1714 (comment)

`command -v <cmd>` is a POSIX shell builtin that prints the path of a command (or the alias/function definition) if it exists, and returns a non-zero exit code if it doesn't. Because it's a shell builtin, it's available in any POSIX-compliant shell (bash, zsh, dash, sh, etc.) without depending on an external binary.

https://stackoverflow.com/questions/592620/how-can-i-check-if-a-program-exists-from-a-bash-script

* Fix failure

```
  1) LanguagePack::Helpers::BinstubCheck can determine if a file is binary or not
     Failure/Error: out = `command -v ruby`.strip

     Errno::ENOENT:
       No such file or directory - command
     # ./spec/helpers/binstub_check_spec.rb:5:in ``'
     # ./spec/helpers/binstub_check_spec.rb:5:in `get_ruby_path!'
     # ./spec/helpers/binstub_check_spec.rb:29:in `block (2 levels) in <top (required)>'
     # ./vendor/bundle/ruby/3.3.0/gems/rspec-core-3.13.6/lib/rspec/core/example.rb:263:in `instance_exec'
     # ./vendor/bundle/ruby/3.3.0/gems/rspec-core-3.13.6/lib/rspec/core/example.rb:263:in `block in run'
     # ./vendor/bundle/ruby/3.3.0/gems/rspec-core-3.13.6/lib/rspec/core/example.rb:511:in `block in with_around_and_singleton_context_hooks'
     # ./vendor/bundle/ruby/3.3.0/gems/rspec-core-3.13.6/lib/rspec/core/example.rb:468:in `block in with_around_example_hooks'
     # ./vendor/bundle/ruby/3.3.0/gems/rspec-core-3.13.6/lib/rspec/core/hooks.rb:486:in `block in run'
     # ./vendor/bundle/ruby/3.3.0/gems/rspec-core-3.13.6/lib/rspec/core/hooks.rb:626:in `block in run_around_example_hooks_for'
     # ./vendor/bundle/ruby/3.3.0/gems/rspec-core-3.13.6/lib/rspec/core/example.rb:352:in `call'
     # ./vendor/bundle/ruby/3.3.0/gems/rspec-retry-0.6.2/lib/rspec/retry.rb:124:in `block in run'
     # <internal:kernel>:187:in `loop'
```

The belief is that the failure mode is due to Ruby trying to lookup `command` on the PATH and not finding it. This behavior is documented in Kernel#exec https://www.rubydoc.info/stdlib/core/Kernel:exec but not on backticks (they use different codepaths, just noting).

Backticks https://ruby-doc.org/3.4.1/Kernel.html#method-i-60 have an issue reported but closed https://bugs.ruby-lang.org/issues/4477.

Adding a stderr redirect triggers the correct behavior.

Author: schneems

bin/support/bash_functions.sh

@@ -33,7 +33,7 @@ curl_retry_on_18() {
 
 which_java()
 {
-  which java > /dev/null
+  command -v java > /dev/null
 }
 
 # Detects if a given Gemfile.lock has jruby in it

lib/language_pack/rails3.rb

@@ -118,13 +118,13 @@ def warn_x_sendfile_use!
   end
 
   def has_apache?
-    path = run("which apachectl")
+    path = run("command -v apachectl")
     return true if path && $?.success?
     false
   end
 
   def has_nginx?
-    path = run("which nginx")
+    path = run("command -v nginx")
     return true if path && $?.success?
     false
   end

lib/language_pack/ruby.rb

@@ -822,7 +822,7 @@ def node_preinstall_bin_path
     return @node_preinstall_bin_path if defined?(@node_preinstall_bin_path)
 
     legacy_path = "#{Dir.pwd}/#{NODE_BP_PATH}"
-    path = run("which node").strip
+    path = run("command -v node").strip
     @node_preinstall_bin_path = if path && $?.success?
       path
     elsif run("#{legacy_path}/node -v") && $?.success?
@@ -850,7 +850,7 @@ def self.yarn_preinstall_bin_path
   def self.yarn_preinstall_binary_path
     return @yarn_preinstall_binary_path if defined?(@yarn_preinstall_binary_path)
 
-    path = run("which yarn").strip
+    path = run("command -v yarn").strip
     @yarn_preinstall_binary_path = if path && $?.success?
       path
     else

spec/hatchet/getting_started_spec.rb

@@ -21,7 +21,7 @@
       # Assert no warnings from `cp`
       # https://github.com/heroku/heroku-buildpack-ruby/pull/1586/files#r2064284286
       expect(app.output).to_not include("cp --help")
-      expect(app.run("which ruby").strip).to eq("/app/bin/ruby")
+      expect(app.run("command -v ruby").strip).to eq("/app/bin/ruby")
 
       environment_variables = app.run("env")
       expect(environment_variables).to match("PUMA_PERSISTENT_TIMEOUT")
@@ -66,7 +66,7 @@
       # Assert no warnings from `cp`
       # https://github.com/heroku/heroku-buildpack-ruby/pull/1586/files#r2064284286
       expect(app.output).to_not include("cp --help")
-      expect(app.run("which ruby").strip).to eq("/app/bin/ruby")
+      expect(app.run("command -v ruby").strip).to eq("/app/bin/ruby")
     end
   end
 end

spec/hatchet/node_spec.rb

@@ -19,8 +19,8 @@
       expect(app.output).to include("Installing a default version (#{LanguagePack::Helpers::Nodebin::YARN_VERSION}) of Yarn")
       expect(app.output).to include("Installing a default version (#{LanguagePack::Helpers::Nodebin::NODE_VERSION}) of Node.js")
 
-      expect(app.run("which node")).to match("/app/bin/node")     # We put node in bin/node
-      expect(app.run("which yarn")).to match("/app/vendor/yarn-") # We put yarn in /app/vendor/yarn-
+      expect(app.run("command -v node")).to match("/app/bin/node")     # We put node in bin/node
+      expect(app.run("command -v yarn")).to match("/app/vendor/yarn-") # We put yarn in /app/vendor/yarn-
     end
   end
 
@@ -37,8 +37,8 @@
       expect(app.output).to include(".heroku/node/bin/yarn is the yarn directory ")
       expect(app.output).to include(".heroku/node/bin/node is the node directory")
 
-      expect(app.run("which node")).to match("/app/.heroku/node/bin")
-      expect(app.run("which yarn")).to match("/app/.heroku/node/bin")
+      expect(app.run("command -v node")).to match("/app/.heroku/node/bin")
+      expect(app.run("command -v yarn")).to match("/app/.heroku/node/bin")
     end
   end
 end

spec/hatchet/ruby_spec.rb

@@ -207,7 +207,7 @@
             raise e
           end
 
-          expect(app.run("which ruby").strip).to eq("/app/bin/ruby")
+          expect(app.run("command -v ruby").strip).to eq("/app/bin/ruby")
         end
       end
     end

spec/helpers/binstub_check_spec.rb

@@ -2,8 +2,8 @@
 
 describe LanguagePack::Helpers::BinstubCheck do
   def get_ruby_path!
-    out = `which ruby`.strip
-    raise "command `which ruby` failed with output: #{out}" unless $?.success?
+    out = `command -v ruby 2>/dev/null`.strip
+    raise "command `command -v ruby` failed with output: #{out}" unless $?.success?
 
     Pathname.new(out)
   end