Command Line – File Manipulation

The most common way to work with data files is to use the copy, cut, and paste keyboard commands (Ctrl+C, Ctrl+X, and Ctrl+V) to edit information between files. On the desktop, these are by far the most efficient methods. However, although the same commands can also be used at the prompt (with a Shift+ as a prefix), the command line offers more alternatives. Instead of keystrokes and applications, commands can be used. Three of the most useful options for manipulating data are parts of the ls and sort commands as well as pipes, which allow commands to be chained in a single line.

ls

Along with cd, the ls command [1] is a basic navigation tool. However, for many users, its main purpose is to locate a file. Today, most distributions create an alias for the bare command with the option --color=auto or set custom colors with the LS_COLORS environment variable to differentiate different kinds of files, but often that is the only additional feature added. Occasionally, --all (-a) is used to include dotfiles, or --almost-all (-A) to exclude them, but since the default is to not display dotfiles as a safety precaution, even these options are rare.

Yet dig a little deeper, and more navigation and mining tools await. Add -l --author to list a file's creator and group. Use --reverse (-r) to list a directory's files in reverse order. Include --recursive (-R) to show the contents of subfolders, or, conversely, use --directory (-d) to list only subfolders. For convenience, --sort=CHOICE sorts directory listings by size (-S), time (-t), version (-v), or extension (-X). If you prefer, you can use --ignore-backups (-B) to not display files ending with ~, --dereference-command-line (-H) to go to the original file and bypass symbolic links, or --hide=PATTERN to exclude files you know are irrelevant. Similarly, -l displays output in a more readable form (Figure 1). You can also use --time=CHOICE to sort by time to display contents by the last time that a file was read (-u), the last time that a file was modified (default), or the last time that file attributes were changed (ctime). In effect, all these options allow much of the sorting options available in a spreadsheet from the command line. Additionally, ls also includes display format options, such as --width=SIZE for column widths, which may make analysis easier in addition to allowing customization.

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