Web Vulnerabilities
Shell Metacharacters
Also: shell special characters
Characters the shell reads as instructions instead of text, such as ; | & $ and backticks.
In more detail
A metacharacter can end a command, chain another, or substitute the output of a third. When input containing them is placed in a command line given to a shell, the input can add commands. Passing arguments as a list, without a shell, means these characters stay ordinary text.