## 3.4. Common Features

The following table displays features that are common to the Bourne, Korn, and C shells. Note that the Korn shell is an enhanced version of the Bourne shell; therefore, the Korn shell includes all features of the Bourne shell, plus some others. The commands `bg`, `fg`, `jobs`, `stop`, and `suspend` are available only on systems that support job control. (Essentially all modern Unix systems do.)

Symbol/Command | Meaning/Action
--- | ---
`>` | Redirect output.
`>>` | Append to file.
`<` | Redirect input.
`<<` | “Here” document (redirect input).
`|` | Pipe output.
`|&` | Start a coprocess. Korn shell only.
`&` | Run process in background.
`;` | Separate commands on same line.
`*` | Match any character(s) in filename.
`?` | Match single character in filename.
`[ ]` | Match any characters enclosed.
`( )` | Execute in subshell.
`‘ ‘` | Substitute output of enclosed command.
`" "` | Partial quote (allows variable and command expansion).
`' '` | Full quote (no expansion).
`\` | Quote following character.
`$``var` | Use value for variable.
`$$` | Process ID.
`$0` | Command name.
`$``n` | nth argument (0 n 9).
`$*` | All arguments as simple words.
`#` | Begin comment.
`bg` | Background execution.
`break` | Break from loop statements.
`cd` | Change directory.
`continue` | Resume a program loop.
`echo` | Display output.
`eval` | Evaluate arguments.
`exec` | Execute a new shell.
`fg` | Foreground execution.
`jobs` | Show active jobs.
`kill` | Terminate running jobs.
`shift` | Shift positional parameters.
`stop` | Suspend a background job.
`suspend` | Suspend a foreground job (such as a shell created by `su`).
`time` | Time a command.
`umask` | Set default file permissions for new files.
`unset` | Erase variable or function definitions.
`wait` | Wait for a background job to finish.

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