By default, Bash “remembers” commands you have entered. This feature is called history. To repeat a command that has been entered before, press ↑ until the desired command appears at the prompt. Press ↓ to move forward through the list of previously entered commands. Use Ctrl-R to search in the history.

You can edit the selected command, for example, changing the name of a file, before you execute the command by pressing Enter. To edit the command line, just move the cursor to the desired position using the arrow keys and start typing.

Completing a filename or directory name to its full length after typing its first letters is another helpful feature of Bash. To do so, type the first letters then press →|. If the filename or path can be uniquely identified, it is completed at once and the cursor moves to the end of the filename. You can then enter the next option of the command, if necessary. If the filename or path cannot be uniquely identified (because there are several filenames starting with the same letters), the filename or path is only completed up to the point where it is again getting ambiguous. You can then obtain a list of the options available by pressing →| a second time. After this, you can enter the next letters of the file or path then try completion again by pressing →|. When completing filenames and paths with →|, you can simultaneously check whether the file or path you want to enter really exists (and you can be sure of getting the spelling right).

Another convenience offered by the shell is wild cards for pathname expansion. Wild cards are characters that can stand for other characters. There are three different types of these in Bash:

Assuming that your test directory contains the files Testfile, Testfile1, Testfile2, and datafile.

Of the four types of wild cards, the most inclusive one is the asterisk. It could be used to copy all files contained in one directory to another one or to delete all files with one command. The command rm *fil*, for instance, would delete all files in the current directory whose name includes the string fil.

Linux includes two small programs for viewing text files directly in the shell: less and more. Rather than starting an editor to read a file like Readme.txt, simply enter less Readme.txt to display the text in the console window. Use Space to scroll down one page. Use Page Up and Page Down to move forward or backward in the text. To exit less, press Q.

Instead of less, you can also use the older program more. However, it is less convenient because it does not allow you to scroll backwards.

The program less got its name from the the precept that less is more and can also be used to view the output of commands in a convenient way. To see how this works, read Section 20.1.2.4, “Redirection and Pipes”.

Normally, the standard output of the shell is your screen or the console window and the standard input is the keyboard. However, the shell provides functions by which you can redirect the input or the output to another object, such as a file or another command. With the help of the symbols > and <, for example, you can forward the output of a command to a file (output redirection) or use a file as input for a command (input redirection). For example, if you want to write the output of a command such as ls to a file, enter ls -l > file.txt. This creates a file named file.txt that contains the list of contents of your current directory as generated by the ls command. However, if a file named file.txt already exists, this command overwrites the existing file. To prevent this, use >>. Entering ls -l >> file.txt simply appends the output of the ls command to an already existing file named file.txt. If the file does not exist, it is created.

Sometimes it is also useful to use a file as the input for a command. For example, with the tr command, you can replace characters redirected from a file and write the result to the standard output, your screen. Suppose you want to replace all characters t of your file.txt from the example above with x and print this to your screen. Do so by entering tr t x < file.txt.

Just like the standard output, the standard error output is sent to the console. To redirect the standard error output to a file named errors, append 2> errors to the corresponding command. Both standard output and standard error are saved to one file named alloutput if you append >& alloutput.

Using pipelines or pipes is also a sort redirection, although the use of the pipe is not constrained to files. With a pipe (|), you can combine several commands, using the output of one command as input for the next command. For example, to view the contents or your current directory in less, enter ls | less. This only makes sense if the normal output with ls would be too lengthy. For instance, if you view the contents of the dev directory with ls /dev, you only see a small portion in the window. View the entire list with ls /dev | less.