Update cheatsheets

tldr/$

@@ -0,0 +1,29 @@
+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# Dollar sign
+
+> Expand a bash variable.
+> More information: <https://gnu.org/software/bash/manual/bash.html#Shell-Variables>.
+
+- Print a variable:
+
+`echo ${{VARIABLE}}`
+
+- Print the exit status of the previous command:
+
+`echo $?`
+
+- Print a random number between 0 and 32767:
+
+`echo $RANDOM`
+
+- Print one of the prompt strings:
+
+`echo ${{PS1|PS2|PS3|PS4}}`
+
+- Expand with the output of `command` and run it. Same as enclosing `command` in backtics:
+
+`$({{command}})`