1 files changed, 146 insertions, 0 deletions
diff --git a/_notes/bash.html b/_notes/bash.html
new file mode 100644
index 0000000..ea0cb8a
--- /dev/null
+++ b/_notes/bash.html
@@ -0,0 +1,146 @@
+---
+title: Bash
+subtitle: best practices
+layout: plain
+features:
+  - title: Arrays
+    topics:
+      - title: Declaration
+        do:
+          - |
+            local -a xs=()
+            declare -a xs=()
+            local -A xs=()
+            declare -A xs=()
+
+            # Works with nounset:
+            echo "${#xs[@]}"
+        dont:
+          - |
+            local -a xs
+            declare -a xs
+            local -A xs
+            declare -A xs
+
+            # Doesn't work with nounset:
+            echo "${#xs[@]}"
+      - title: Expansion
+        do:
+          - |
+            func ${arr[@]+"${arr[@]}"}
+        dont:
+          - |
+            # Doesn't work with nounset:
+            func "${arr[@]}"
+            # Doesn't work properly with `declare -a arr=('')`:
+            func "${arr[@]+"${arr[@]}"}"
+      - title: unset
+        do:
+          - |
+            unset -v 'arr[x]'
+            unset -v 'arr[$i]'
+        dont:
+          - |
+            # May break due to globbing:
+            unset -v arr[x]
+            # In addition, possible quoting problem:
+            unset -v arr[$i]
+            # Doesn't work for some reason:
+            unset -v 'arr["x"]'
+            unset -v 'arr["]"]'
+            # Also rejected:
+            unset -v 'arr["$i"]'
+
+            # An insightful discussion on the topic:
+            # https://lists.gnu.org/archive/html/help-bash/2016-09/msg00020.html
+  - title: errexit
+    topics:
+      - title: Command substitution
+        do:
+          - |
+            # Without this, bar will be executed w/ errexit disabled!
+            shopt -s inherit_errexit
+
+            bar() {
+                false
+                echo 'should never see this' >&2
+            }
+
+            bar_output="$( bar )"
+            foo "$bar_output"
+        dont:
+          - |
+            bar() {
+                false
+                echo 'should never see this' >&2
+            }
+
+            # Even with errexit, foo will still get executed.
+            # More than that, the script will print 'should never see this'!
+            foo "$( bar )"
+      - title: Process substitution
+        do:
+          - |
+            shopt -s lastpipe
+
+            command | while IFS= read -r line; do
+                process_line "$line"
+            done
+        dont:
+          - |
+            # Without lastpipe, you cannot pipe into read:
+            command | while IFS= read -r line; do
+                process_line "$line"
+            done
+          - |
+            # errexit doesn't work here no matter what:
+            while IFS= read -r line; do
+                process_line "$line"
+            done < <( command )
+            echo 'should never see this'
+          - |
+            # This would break if $output contains the \0 byte:
+            output="$( command )"
+
+            while IFS= read -r line; do
+                process_line "$line"
+            done <<< "$output"
+      - title: Functions
+        do:
+          - |
+            foo() {
+                false
+                echo 'should never see this' >&2
+            }
+
+            foo
+            echo ok
+        dont:
+          - |
+            # foo will still print 'should never see this'.
+            if foo; then
+                echo ok
+            fi
+
+            # Same below.
+            foo && echo ok
+            foo || echo ok
+---
+{% for feature in page.features %}
+  <h2>{{ feature.title }}</h2>
+  {% for topic in feature.topics %}
+    <h3>{{ topic.title }}</h3>
+    <div class="row">
+      <div class="col-md-6">
+        {% for guide in topic.do %}
+          {% highlight bash %}{{ guide }}{% endhighlight %}
+        {% endfor %}
+      </div>
+      <div class="col-md-6">
+        {% for guide in topic.dont %}
+          {% highlight bash %}{{ guide }}{% endhighlight %}
+        {% endfor %}
+      </div>
+    </div>
+  {% endfor %}
+{% endfor %}