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Programming with the UNIX system shell

Shell command language

This section introduces commands and, more importantly, special characters that let you

``Characters with special meanings in the shell language'' summarizes the characters that have special meanings in the shell.

Characters with special meanings in the shell language

Character Function
* ? [ ] The asterisk, question mark, and brackets allow you to specify filenames by pattern matching.
& The ampersand places commands in background mode, leaving your terminal free for other tasks.
; The semicolon separates multiple commands on one command line.
\ The backslash turns off the meaning of special characters such as * ? [ ] & ; > < and |.
' . . . ' Single quotes turn off the delimiting meaning of a space and the special meaning of all special characters.
" . . . " Double quotes turn off the delimiting meaning of a space and the special meaning of all special characters except $ and `.
> The greater than sign redirects the output of a command into a file (replacing the existing contents).
< The less than sign redirects the input for a command to come from a file.
>> Two greater than signs redirect the output of a command to be added to the end of an existing file.
| The vertical bar, or pipe, makes the output of one command the input of another command.
` . . . ` A pair of grave accents around a command embedded on a command line makes the output of the embedded command an argument on the larger command line.
$ The dollar sign retrieves the value of positional parameters and user-defined variables. It is also the default shell prompt.


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