Updated SC2154 (markdown)

SC2154.md

@@ -1,63 +1,6 @@
-## var is referenced but not assigned.
+RUN \
-
+  export http_proxy=${http_proxy}; \
-### Problematic code:
+  export https_proxy=${https_proxy}; \
-
+  dnf -y upgrade; \
-```sh
+  dnf -y install libXext libXrender libXtst xorg-x11-server-Xvfb fontconfig unzip sudo telnet; \
-var=name
+  dnf -y clean all
-n=42
-echo "$var_$n.jpg"   # overextended
-```
-
-or
-
-```sh
-target="world"
-echo "hello $tagret"  # misspelled
-```
-
-or
-
-```sh
-echo "Result: ${mycmd -a myfile}"  # trying to execute commands
-```
-
-### Correct code:
-
-```sh
-var=name
-n=42
-echo "${var}_${n}.jpg"
-```
-
-or
-
-```sh
-target="world"
-echo "hello $target"
-```
-
-or
-
-```sh
-echo "Result: $(mycmd -a myfile)"
-```
-
-### Rationale:
-
-ShellCheck has noticed that you reference a variable that is not assigned. Double check that the variable is indeed assigned, and that the name is not misspelled.
-
-Note: This message only triggers for variables with lowercase characters in their name (`foo` and `kFOO` but not `FOO`) due to the standard convention of using lowercase variable names for unexported, local variables.
-
-### Exceptions:
-
-ShellCheck intentionally does not attempt to figure out runtime or dynamic assignments like with `source "$(date +%F).sh"` or `eval var=value`. See [[SC2034]] for an extended discussion of why this is the case.
-
-If you know for a fact that the variable is set, you can use `${var:?}` to fail if the variable is unset (or empty), initialize it to a default value if uninitialized with `: "${var:=}"`, or explicitly initialize/declare it with `var=""` or `declare var`. You can also disable the message with a [[directive]].
-
----
-
-## Read more:
-
-POSIX - Parameter expansion:
-* https://stackoverflow.com/a/16753536/2309247
-* http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_02