Add Compare Two Variables In A Bash Script as a unix til

unix/compare-two-variables-in-a-bash-script.md

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+# Compare Two Variables In A Bash Script
+
+You can compare two variables in a bash script with an `if` block like so:
+
+```bash
+if [ "$EDITOR" = "$PREFERRED_EDITOR" ]; then
+  # do something ...
+fi
+```
+
+If those variables are equal, then the contents of the `if` block will be
+executed.
+
+Notice that both variables are wrapped in quotes. This is to avoid a potential
+syntax error. If the quotes were excluded and one of the variables happened to
+be unset, then the comparison would evaluate to:
+
+```bash
+if [ "vim" = ]; then
+  # do something ...
+fi
+```
+
+That would cause an error, rather than evaluating to false and moving in.
+Wrapping each in quotes allows an unset variable to turn into an empty string
+(`""`).