GNU and Unix Commands

Objective 1: Work Effectively on the Command Line

The interactive shell and shell variables

  • A shell provides the command prompt and interprets commands.

  • A shell variable holds a value that is accessible to shell programs.

  • PATH is a shell variable that contains a listing of directories that hold executable programs.

  • Commands must be bash built-ins, found in the PATH, or explicitly defined in order to succeed.

  • When shell variables are exported, they become part of the environment.

Entering commands

  • Commands are comprised of a valid command, with or without one or more options and arguments, followed by a carriage return.

  • Interactive commands can include looping structures more often used in shell scripts.

Command history, editing, and substitution

  • Shell sessions can be viewed as a conversation. History, expansion, and editing make that dialog more productive.

  • Commands can be reissued, modified, and edited. Examples are shown in Table 10-2.

  • Command substitution allows the result of a command to be placed into a shell variable.

Table 10-2. Shell expansion, editing, and substitution examples

History type









Ctrl-P, previous line


Ctrl-K, kill to end of line


Ctrl-Y, paste (yank) text



Recursive execution

  • Many commands contain either a -r or -R option for recursive execution through a directory hierarchy.

  • The find command is inherently recursive, and is intended to descend through directories ...

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