Created SC2005 (markdown)

SC2005.md

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+Useless `echo`? Instead of `echo $(cmd)`, just use `cmd`
+--------------------------------------------------------
+
+### Problematic code:
+
+```sh
+echo "$(cat 1.txt)"
+echo `< /dev/urandom tr -dc _A-Z-a-z-0-9 | head -c6`
+```
+
+### Correct code:
+
+```sh
+cat 1.txt # In bash, but faster and still sticks exactly one newline: printf '%s\n' "$(<1.txt)"
+# The original `echo` sticks a newline; we want it too.
+< /dev/urandom tr -dc _A-Z-a-z-0-9 | head -c6; echo
+```
+
+### Rationale
+
+The command substitution `$(foo)` yields the result of command `foo` with trailing newlines erased, and when it is passed to `echo` it generally just gives the same result as `foo`.
+
+### Exceptions
+
+One may want to use command substitutions plus `echo` to make sure there is exactly one trailing newline. The special command substitution `$(<file)` in `bash` is also un-outline-able.
+
+Anyway, echo is still not that reliable (see [[SC2039#echo-flags]]) and `printf` should be used instead.