Chapter 2 . Running Commands from the Shell (Web proxy server)
Chapter 2 . Running Commands from the Shell 55 You could make that your current directory by typing cd $M. You could run a program from that directory called hotdog by typing $M/hotdog. You could edit a file from there called bun by typing vi $M/bun. Adding Aliases Setting aliases can save you even more typing than setting environment variables. With aliases, you can have a string of characters execute an entire command line. You can add and list aliases with the alias command. Here are some examples: alias p= pwd ; ls CF alias rm= rm -i alias p= pwd ; ls -CF alias rm= rm -i In the first example, the letter p is assigned to run the command pwd, and then to run ls -CF to print the current working directory and list its contents in column form. The second runs the rm command with the -i option each time you simply type rm. (This is an alias that is often set automatically for the root user, so that instead of just removing files, you are prompted for each individual file removal. This prevents you from removing all the files in a directory by mistakenly typing something such as rm *.) While you are in the shell, you can check which aliases are set by typing the alias command. If you want to remove an alias, type unalias. (Remember that if the alias is set in a configuration file, it will be set again when you open another shell.) Using Shell Environment Variables Every active shell stores pieces of information that it needs to use in what are called environment variables. An environment variable can store things such as locations of configuration files, mailboxes, and path directories. They can also store values for your shell prompts, the size of your history list, and type of operating system. To see the environment variables currently assigned to your shell, type the declare command. (It will probably fill more than one screen, so type declare | more.) You can refer to the value of any of those variables by preceding it with a dollar sign ($) and placing it anywhere on a command line. For example: $ echo $USER chris This command prints the value of the USER variable, which holds your username (chris). Substitute any other value for USER to print its value instead.
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