1.1 Your First Steps with the Command Line - Modern Software Development Practices

mkdir -p ../home/ch1
cd ../home/ch1

Before we jump into the world of Git, let’s first get comfortable with the command line. This section will introduce you to the basic commands that are essential for navigating your computer and managing files.

The Command Line Interface¶

The command line is a powerful, text-based tool for interacting with your computer. It allows you to perform tasks, manage files, and run programs by typing commands instead of clicking on icons.

The Prompt¶

When you open the command line, you are greeted by the prompt. It typically shows information like your username, the machine’s name (hostname), and your current location (directory). For example:

user@hostname:~$

Let’s break this down:

user: The current logged-in user.
hostname: The name of the computer.
~: A shortcut for your home directory.
$: A standard symbol indicating you are logged in as a regular user. An administrator (or root) user often sees a # symbol.

Where Am I? Finding Your Place¶

The first thing you need to know is how to find out where you are in the file system.

To display the full path of your current directory, use the pwd (print working directory) command:

pwd

/home/runner/work/msdp-book/msdp-book/home/ch1

This command will print the absolute path from the root of the file system (/) to your current location.

Now that you know where you are, let’s see what’s in there. To list the files and directories in your current location, use the ls (list) command:

ls

Navigating the File System¶

Knowing where you are is useful, but you’ll often need to move around. The cd (change directory) command is your tool for navigation.

First, let’s create a new directory to practice with. To create a directory, use the mkdir (make directory) command:

mkdir my-test-folder

Now, to move into your new my-test-folder directory, use cd followed by the directory name:

cd my-test-folder

You can confirm your new location with pwd:

pwd

/home/runner/work/msdp-book/msdp-book/home/ch1/my-test-folder

To go back up one level to the parent directory, you can use the special .. argument:

cd ..

Creating and Managing Files¶

Now that you can navigate, let’s create and work with files.

To create a new, empty file, use the touch command:

touch notes.txt

To add content to a file, you can use the echo command combined with the > redirection operator.

echo "Hello, Command Line!" > notes.txt

To display the content of your new file, use the cat (concatenate) command:

cat notes.txt

Hello, Command Line!

Cleaning Up Your Workspace¶

To keep things tidy, you’ll need to know how to delete files and directories.

To remove a file, use the rm (remove) command:

rm notes.txt

To remove an empty directory, you can use rmdir. However, to remove a directory and all the files and subdirectories inside it, you need to use rm with the -r (recursive) option.

Let’s remove the my-test-folder directory we created earlier:

rm -r my-test-folder

Getting Help¶

Almost every command has a help page that lists its options and how to use them. To see it, you can usually use the --help flag.

ls --help

Usage: ls [OPTION]... [FILE]...

List information about the FILEs (the current directory by default).

Sort entries alphabetically if none of -cftuvSUX nor --sort is specified.

Mandatory arguments to long options are mandatory for short options too.

  -a, --all                  do not ignore entries starting with .

  -A, --almost-all           do not list implied . and ..

      --author               with -l, print the author of each file

  -b, --escape               print C-style escapes for nongraphic characters

      --block-size=SIZE      with -l, scale sizes by SIZE when printing them;

                             e.g., '--block-size=M'; see SIZE format below

  -B, --ignore-backups       do not list implied entries ending with ~

  -c                         with -lt: sort by, and show, ctime (time of last

                             change of file status information);

                             with -l: show ctime and sort by name;

                             otherwise: sort by ctime, newest first

  -C                         list entries by columns

      --color[=WHEN]         color the output WHEN; more info below

  -d, --directory            list directories themselves, not their contents

  -D, --dired                generate output designed for Emacs' dired mode

  -f                         list all entries in directory order

  -F, --classify[=WHEN]      append indicator (one of */=>@|) to entries WHEN

      --file-type            likewise, except do not append '*'

      --format=WORD          across -x, commas -m, horizontal -x, long -l,

                             single-column -1, verbose -l, vertical -C

      --full-time            like -l --time-style=full-iso

  -g                         like -l, but do not list owner

      --group-directories-first

                             group directories before files;

                             can be augmented with a --sort option, but any

                             use of --sort=none (-U) disables grouping

  -G, --no-group             in a long listing, don't print group names

  -h, --human-readable       with -l and -s, print sizes like 1K 234M 2G etc.

      --si                   likewise, but use powers of 1000 not 1024

  -H, --dereference-command-line

                             follow symbolic links listed on the command line

      --dereference-command-line-symlink-to-dir

                             follow each command line symbolic link

                             that points to a directory

      --hide=PATTERN         do not list implied entries matching shell PATTERN

                             (overridden by -a or -A)

      --hyperlink[=WHEN]     hyperlink file names WHEN

      --indicator-style=WORD

                             append indicator with style WORD to entry names:

                             none (default), slash (-p),

                             file-type (--file-type), classify (-F)

  -i, --inode                print the index number of each file

  -I, --ignore=PATTERN       do not list implied entries matching shell PATTERN

  -k, --kibibytes            default to 1024-byte blocks for file system usage;

                             used only with -s and per directory totals

  -l                         use a long listing format

  -L, --dereference          when showing file information for a symbolic

                             link, show information for the file the link

                             references rather than for the link itself

  -m                         fill width with a comma separated list of entries

  -n, --numeric-uid-gid      like -l, but list numeric user and group IDs

  -N, --literal              print entry names without quoting

  -o                         like -l, but do not list group information

  -p, --indicator-style=slash

                             append / indicator to directories

  -q, --hide-control-chars   print ? instead of nongraphic characters

      --show-control-chars   show nongraphic characters as-is (the default,

                             unless program is 'ls' and output is a terminal)

  -Q, --quote-name           enclose entry names in double quotes

      --quoting-style=WORD   use quoting style WORD for entry names:

                             literal, locale, shell, shell-always,

                             shell-escape, shell-escape-always, c, escape

                             (overrides QUOTING_STYLE environment variable)

  -r, --reverse              reverse order while sorting

  -R, --recursive            list subdirectories recursively

  -s, --size                 print the allocated size of each file, in blocks

  -S                         sort by file size, largest first

      --sort=WORD            sort by WORD instead of name: none (-U), size (-S),

                             time (-t), version (-v), extension (-X), width

      --time=WORD            select which timestamp used to display or sort;

                               access time (-u): atime, access, use;

                               metadata change time (-c): ctime, status;

                               modified time (default): mtime, modification;

                               birth time: birth, creation;

                             with -l, WORD determines which time to show;

                             with --sort=time, sort by WORD (newest first)

      --time-style=TIME_STYLE

                             time/date format with -l; see TIME_STYLE below

  -t                         sort by time, newest first; see --time

  -T, --tabsize=COLS         assume tab stops at each COLS instead of 8

  -u                         with -lt: sort by, and show, access time;

                             with -l: show access time and sort by name;

                             otherwise: sort by access time, newest first

  -U                         do not sort; list entries in directory order

  -v                         natural sort of (version) numbers within text

  -w, --width=COLS           set output width to COLS.  0 means no limit

  -x                         list entries by lines instead of by columns

  -X                         sort alphabetically by entry extension

  -Z, --context              print any security context of each file

      --zero                 end each output line with NUL, not newline

  -1                         list one file per line

      --help        display this help and exit

      --version     output version information and exit

The SIZE argument is an integer and optional unit (example: 10K is 10*1024).

Units are K,M,G,T,P,E,Z,Y,R,Q (powers of 1024) or KB,MB,... (powers of 1000).

Binary prefixes can be used, too: KiB=K, MiB=M, and so on.

The TIME_STYLE argument can be full-iso, long-iso, iso, locale, or +FORMAT.

FORMAT is interpreted like in date(1).  If FORMAT is FORMAT1<newline>FORMAT2,

then FORMAT1 applies to non-recent files and FORMAT2 to recent files.

TIME_STYLE prefixed with 'posix-' takes effect only outside the POSIX locale.

Also the TIME_STYLE environment variable sets the default style to use.

The WHEN argument defaults to 'always' and can also be 'auto' or 'never'.

Using color to distinguish file types is disabled both by default and

with --color=never.  With --color=auto, ls emits color codes only when

standard output is connected to a terminal.  The LS_COLORS environment

variable can change the settings.  Use the dircolors(1) command to set it.

Exit status:

 0  if OK,

 1  if minor problems (e.g., cannot access subdirectory),

 2  if serious trouble (e.g., cannot access command-line argument).

GNU coreutils online help: <https://www.gnu.org/software/coreutils/>

Report any translation bugs to <https://translationproject.org/team/>

Full documentation <https://www.gnu.org/software/coreutils/ls>

or available locally via: info '(coreutils) ls invocation'