9.3 Entering Commands at the Prompt

Commands are entered at the shell command prompt simply by typing the command and pressing the Enter key. While some commands perform tasks silently, most will display some form of output before returning to the prompt. For example, the ls command can be used to display the files and directories in the current working directory:

$ ls

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The available commands are either built into the shell itself, or reside on the physical file system. The location on the file system of a command may be identified using the which command. For example, to find out where the ls executable resides on the file system:

$ which ls

alias ls=’ls --color=auto’

/usr/bin/ls

Clearly the ls command resides in the /usr/bin directory. Note also that an alias is configured, a topic which will be covered later in this chapter. Using the which command to locate the path to commands that are built into the shell will result in a message indicating the executable cannot be found. For example, attempting to find the location of the history command (which is actually built into the shell rather than existing as an executable on the file system) will result in output similar to the following:

$ which history

/usr/bin/which: no history in (/home/demo/.local/bin:/home/demo/bin:/usr/share/Modules/bin:/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin)