/bin/zsh
Lecture 03: Command Line Interface
Department of Quantitative Theory and Methods
Emory University
09 September, 2024
Credit Dave Kerr
Credit Dave Kerr/Kkchaudhary11
Credit Dave Kerr
Credit Dave Kerr
Terminals are really quite simple - they’re just interfaces
The first thing that a terminal will do is run a shell - a programme we can use to operate the computer
Back to the shell: the shell usually takes input
In interactive mode the shell then returns output
The command line represents what is shown and entered in the terminal. They can be customised (e.g., with colour highlighting) to make interaction more convenient
Why should you use this…
… instead of this?
Speed. Typing is fast: A skilled shell user can manipulate a system at dazzling speeds just using a keyboard. Typing commands is generally much faster than exploring through user interfaces with a mouse.
Power. Both for executing commands and for fixing problems. There are some things you just can’t do in an IDE or GUI. It also avoids memory complications associated with certain applications and/or IDEs.
Reproducibility. Scripting is reproducible, while clicking is not.
Portability. A shell can be used to interface to almost any type of computer, from a mainframe to a Raspberry Pi, in a very similar way. The shell is often the only game in town for high performance computing (interacting with servers and super computers).
Automation. Shells are programmable: Working in the shell allows you to program workflows, that is create scripts to automate time-consuming or repetitive processes.
Become a marketable data scientist. Modern programming is often polyglot. The shell provides a common interface for tooling. Modern solutions are often built to run in containers on Linux. In this environment shell knowledge has become very valuable. In short, the shell is having a renaissance in the age of data science.
The shell tools that we’re going to be using have their roots in the Unix family of operating systems originally developed at Bells Labs in the 1970s.
Besides paying homage, acknowledging the Unix lineage is important because these tools still embody the “Unix philosophy”:
Do One Thing And Do It Well
By pairing and chaining well-designed individual components, we can build powerful and much more complex larger systems.
You can see why the Unix philosophy is also referred to as “minimalist and modular”.
Again, this philosophy is very clearly expressed in the design and functionality of the Unix shell.
Let’s open up our shell!
A convenient way to do this is through VS Code’s built-in Terminal.
Click on the View menu, then Terminal. You can also use the shortcut Ctrl + `
(backtick).
Your system default shell is loaded. To find out what that is, type echo $SHELL
in the terminal.
It is Z shell in my case
… what about you? It is your turn to find out!
Of course, it’s always possible to open up the shell directly if you prefer. It’s your turn!
Feel free to check our class tutorial on how to set up your shell in VS Code.
You should see something like:
This is shell-speak for: “Who am I and where am I?”
username
denotes a specific user (one of potentially many on this computer).
@hostname
denotes the name of the computer or server.
:~
denotes the directory path (where ~
signifies the user’s home directory).
$
(or maybe %
) denotes the start of the command prompt.
#
).All bash commands have the same basic syntax:
command option(s) argument(s)
Examples:
Commands
You don’t always need options or arguments
For example:
ls ~/Documents/
and ls -lh ~/Documents
are both valid commands that will yield (different) outputHowever, you always need a command.
All Bash commands have the same basic syntax:
command option(s) argument(s)
Examples:
Options (also called Flags)
Start with a dash. Usually one letter.
Multiple options can be chained under a single dash.
l
: Use a long listing format. This option shows detailed information about the files and directories
h
: With -l
, print sizes in human-readable format (e.g., KB, MB)
u
: Unique, it filters out the duplicate entries in the output
Think it’s difficult to memorize what the individual letters stand for? You’re totally right!
All Bash commands have the same basic syntax:
command option(s) argument(s)
Examples:
The man
tool can be used to look at the manual page for a topic.
The man
pages are grouped into sections, we can see them with man man
.
The cht.sh
website can be used directly from the shell to get help on tools. Run it like this: curl cht.sh/command
tldr
tool which provides simplified help pages for common commands. Run it like this: tldr command
ls
List directory contents.
More information: https://www.gnu.org/software/coreutils/ls.
List files one per line:
ls -1
List all files, including hidden files:
ls -a
List all files, with trailing / added to directory names:
ls -F
Long format list (permissions, ownership, size, and modification date) of all files:
ls -la
Long format list with size displayed using human-readable units (KiB, MiB, GiB):
ls -lh
Long format list sorted by size (descending) recursively:
ls -lSR
Long format list of all files, sorted by modification date (oldest first):
ls -ltr
Only list directories:
ls -d */
man
The man
command (“manual pages”) is your friend if you need help.
LS(1) General Commands Manual LS(1)
NNAAMMEE
llss – list directory contents
SSYYNNOOPPSSIISS
llss [--@@AABBCCFFGGHHIILLOOPPRRSSTTUUWWaabbccddeeffgghhiikkllmmnnooppqqrrssttuuvvwwxxyy11%%,,] [----ccoolloorr=_w_h_e_n]
[--DD _f_o_r_m_a_t] [_f_i_l_e _._._.]
DDEESSCCRRIIPPTTIIOONN
For each operand that names a _f_i_l_e of a type other than directory, llss
displays its name as well as any requested, associated information. For
each operand that names a _f_i_l_e of type directory, llss displays the names of
files contained within that directory, as well as any requested, associated
information.
If no operands are given, the contents of the current directory are
displayed. If more than one operand is given, non-directory operands are
displayed first; directory and non-directory operands are sorted separately
and in lexicographical order.
The following options are available:
--@@ Display extended attribute keys and sizes in long (--ll) output.
--AA Include directory entries whose names begin with a dot (‘_.’) except
for _. and _._.. Automatically set for the super-user unless --II is
specified.
--BB Force printing of non-printable characters (as defined by ctype(3)
and current locale settings) in file names as \_x_x_x, where _x_x_x is
the numeric value of the character in octal. This option is not
defined in IEEE Std 1003.1-2008 (“POSIX.1”).
--CC Force multi-column output; this is the default when output is to a
terminal.
--DD _f_o_r_m_a_t
When printing in the long (--ll) format, use _f_o_r_m_a_t to format the
date and time output. The argument _f_o_r_m_a_t is a string used by
strftime(3). Depending on the choice of format string, this may
result in a different number of columns in the output. This option
overrides the --TT option. This option is not defined in IEEE Std
1003.1-2008 (“POSIX.1”).
--FF Display a slash (‘/’) immediately after each pathname that is a
directory, an asterisk (‘*’) after each that is executable, an at
sign (‘@’) after each symbolic link, an equals sign (‘=’) after
each socket, a percent sign (‘%’) after each whiteout, and a
vertical bar (‘|’) after each that is a FIFO.
--GG Enable colorized output. This option is equivalent to defining
CLICOLOR or COLORTERM in the environment and setting ----ccoolloorr=_a_u_t_o.
(See below.) This functionality can be compiled out by removing
the definition of COLORLS. This option is not defined in IEEE Std
1003.1-2008 (“POSIX.1”).
--HH Symbolic links on the command line are followed. This option is
assumed if none of the --FF, --dd, or --ll options are specified.
--II Prevent --AA from being automatically set for the super-user. This
option is not defined in IEEE Std 1003.1-2008 (“POSIX.1”).
--LL Follow all symbolic links to final target and list the file or
directory the link references rather than the link itself. This
option cancels the --PP option.
--OO Include the file flags in a long (--ll) output. This option is
incompatible with IEEE Std 1003.1-2008 (“POSIX.1”). See chflags(1)
for a list of file flags and their meanings.
--PP If argument is a symbolic link, list the link itself rather than
the object the link references. This option cancels the --HH and --LL
options.
--RR Recursively list subdirectories encountered.
--SS Sort by size (largest file first) before sorting the operands in
lexicographical order.
--TT When printing in the long (--ll) format, display complete time
information for the file, including month, day, hour, minute,
second, and year. The --DD option gives even more control over the
output format. This option is not defined in IEEE Std 1003.1-2008
(“POSIX.1”).
--UU Use time when file was created for sorting or printing. This
option is not defined in IEEE Std 1003.1-2008 (“POSIX.1”).
--WW Display whiteouts when scanning directories. This option is not
defined in IEEE Std 1003.1-2008 (“POSIX.1”).
--aa Include directory entries whose names begin with a dot (‘_.’).
--bb As --BB, but use C escape codes whenever possible. This option is
not defined in IEEE Std 1003.1-2008 (“POSIX.1”).
--cc Use time when file status was last changed for sorting or printing.
----ccoolloorr=_w_h_e_n
Output colored escape sequences based on _w_h_e_n, which may be set to
either aallwwaayyss, aauuttoo, or nneevveerr.
aallwwaayyss will make llss always output color. If TERM is unset or set
to an invalid terminal, then llss will fall back to explicit ANSI
escape sequences without the help of termcap(5). aallwwaayyss is the
default if ----ccoolloorr is specified without an argument.
aauuttoo will make llss output escape sequences based on termcap(5), but
only if stdout is a tty and either the --GG flag is specified or the
COLORTERM environment variable is set and not empty.
nneevveerr will disable color regardless of environment variables.
nneevveerr is the default when neither ----ccoolloorr nor --GG is specified.
For compatibility with GNU coreutils, llss supports yyeess or ffoorrccee as
equivalent to aallwwaayyss, nnoo or nnoonnee as equivalent to nneevveerr, and ttttyy or
iiff--ttttyy as equivalent to aauuttoo.
--dd Directories are listed as plain files (not searched recursively).
--ee Print the Access Control List (ACL) associated with the file, if
present, in long (--ll) output.
--ff Output is not sorted. This option turns on --aa. It also negates
the effect of the --rr, --SS and --tt options. As allowed by IEEE Std
1003.1-2008 (“POSIX.1”), this option has no effect on the --dd, --ll,
--RR and --ss options.
--gg This option has no effect. It is only available for compatibility
with 4.3BSD, where it was used to display the group name in the
long (--ll) format output. This option is incompatible with IEEE Std
1003.1-2008 (“POSIX.1”).
--hh When used with the --ll option, use unit suffixes: Byte, Kilobyte,
Megabyte, Gigabyte, Terabyte and Petabyte in order to reduce the
number of digits to four or fewer using base 2 for sizes. This
option is not defined in IEEE Std 1003.1-2008 (“POSIX.1”).
--ii For each file, print the file's file serial number (inode number).
--kk This has the same effect as setting environment variable BLOCKSIZE
to 1024, except that it also nullifies any --hh options to its left.
--ll (The lowercase letter “ell”.) List files in the long format, as
described in the _T_h_e _L_o_n_g _F_o_r_m_a_t subsection below.
--mm Stream output format; list files across the page, separated by
commas.
--nn Display user and group IDs numerically rather than converting to a
user or group name in a long (--ll) output. This option turns on the
--ll option.
--oo List in long format, but omit the group id.
--pp Write a slash (‘/’) after each filename if that file is a
directory.
--qq Force printing of non-graphic characters in file names as the
character ‘?’; this is the default when output is to a terminal.
--rr Reverse the order of the sort.
--ss Display the number of blocks used in the file system by each file.
Block sizes and directory totals are handled as described in _T_h_e
_L_o_n_g _F_o_r_m_a_t subsection below, except (if the long format is not
also requested) the directory totals are not output when the output
is in a single column, even if multi-column output is requested.
(--ll) format, display complete time information for the file,
including month, day, hour, minute, second, and year. The --DD
option gives even more control over the output format. This option
is not defined in IEEE Std 1003.1-2008 (“POSIX.1”).
--tt Sort by descending time modified (most recently modified first).
If two files have the same modification timestamp, sort their names
in ascending lexicographical order. The --rr option reverses both of
these sort orders.
Note that these sort orders are contradictory: the time sequence is
in descending order, the lexicographical sort is in ascending
order. This behavior is mandated by IEEE Std 1003.2 (“POSIX.2”).
This feature can cause problems listing files stored with
sequential names on FAT file systems, such as from digital cameras,
where it is possible to have more than one image with the same
timestamp. In such a case, the photos cannot be listed in the
sequence in which they were taken. To ensure the same sort order
for time and for lexicographical sorting, set the environment
variable LS_SAMESORT or use the --yy option. This causes llss to
reverse the lexicographical sort order when sorting files with the
same modification timestamp.
--uu Use time of last access, instead of time of last modification of
the file for sorting (--tt) or long printing (--ll).
--vv Force unedited printing of non-graphic characters; this is the
default when output is not to a terminal.
--ww Force raw printing of non-printable characters. This is the
default when output is not to a terminal. This option is not
defined in IEEE Std 1003.1-2001 (“POSIX.1”).
--xx The same as --CC, except that the multi-column output is produced
with entries sorted across, rather than down, the columns.
--yy When the --tt option is set, sort the alphabetical output in the same
order as the time output. This has the same effect as setting
LS_SAMESORT. See the description of the --tt option for more
details. This option is not defined in IEEE Std 1003.1-2001
(“POSIX.1”).
--%% Distinguish dataless files and directories with a '%' character in
long
--11 (The numeric digit “one”.) Force output to be one entry per line.
This is the default when output is not to a terminal. (--ll) output,
and don't materialize dataless directories when listing them.
--, (Comma) When the --ll option is set, print file sizes grouped and
separated by thousands using the non-monetary separator returned by
localeconv(3), typically a comma or period. If no locale is set,
or the locale does not have a non-monetary separator, this option
has no effect. This option is not defined in IEEE Std 1003.1-2001
(“POSIX.1”).
The --11, --CC, --xx, and --ll options all override each other; the last one
specified determines the format used.
The --cc, --uu, and --UU options all override each other; the last one specified
determines the file time used.
The --SS and --tt options override each other; the last one specified
determines the sort order used.
The --BB, --bb, --ww, and --qq options all override each other; the last one
specified determines the format used for non-printable characters.
The --HH, --LL and --PP options all override each other (either partially or
fully); they are applied in the order specified.
By default, llss lists one entry per line to standard output; the exceptions
are to terminals or when the --CC or --xx options are specified.
File information is displayed with one or more ⟨blank⟩s separating the
information associated with the --ii, --ss, and --ll options.
TThhee LLoonngg FFoorrmmaatt
If the --ll option is given, the following information is displayed for each
file: file mode, number of links, owner name, group name, number of bytes
in the file, abbreviated month, day-of-month file was last modified, hour
file last modified, minute file last modified, and the pathname. If the
file or directory has extended attributes, the permissions field printed by
the --ll option is followed by a '@' character. Otherwise, if the file or
directory has extended security information (such as an access control
list), the permissions field printed by the --ll option is followed by a '+'
character. If the --%% option is given, a '%' character follows the
permissions field for dataless files and directories, possibly replacing
the '@' or '+' character.
If the modification time of the file is more than 6 months in the past or
future, and the --DD or --TT are not specified, then the year of the last
modification is displayed in place of the hour and minute fields.
If the owner or group names are not a known user or group name, or the --nn
option is given, the numeric ID's are displayed.
If the file is a character special or block special file, the device number
for the file is displayed in the size field. If the file is a symbolic
link the pathname of the linked-to file is preceded by “->”.
The listing of a directory's contents is preceded by a labeled total number
of blocks used in the file system by the files which are listed as the
directory's contents (which may or may not include _. and _._. and other files
which start with a dot, depending on other options).
The default block size is 512 bytes. The block size may be set with option
--kk or environment variable BLOCKSIZE. Numbers of blocks in the output will
have been rounded up so the numbers of bytes is at least as many as used by
the corresponding file system blocks (which might have a different size).
The file mode printed under the --ll option consists of the entry type and
the permissions. The entry type character describes the type of file, as
follows:
-- Regular file.
bb Block special file.
cc Character special file.
dd Directory.
ll Symbolic link.
pp FIFO.
ss Socket.
ww Whiteout.
The next three fields are three characters each: owner permissions, group
permissions, and other permissions. Each field has three character
positions:
1. If rr, the file is readable; if --, it is not readable.
2. If ww, the file is writable; if --, it is not writable.
3. The first of the following that applies:
SS If in the owner permissions, the file is not
executable and set-user-ID mode is set. If in the
group permissions, the file is not executable and
set-group-ID mode is set.
ss If in the owner permissions, the file is executable
and set-user-ID mode is set. If in the group
permissions, the file is executable and setgroup-ID
mode is set.
xx The file is executable or the directory is
searchable.
-- The file is neither readable, writable, executable,
nor set-user-ID nor set-group-ID mode, nor sticky.
(See below.)
These next two apply only to the third character in the last
group (other permissions).
TT The sticky bit is set (mode 1000), but not execute
or search permission. (See chmod(1) or sticky(7).)
tt The sticky bit is set (mode 1000), and is searchable
or executable. (See chmod(1) or sticky(7).)
The next field contains a plus (‘+’) character if the file has an ACL, or a
space (‘ ’) if it does not. The llss utility does not show the actual ACL;
use getfacl(1) to do this.
EENNVVIIRROONNMMEENNTT
The following environment variables affect the execution of llss:
BLOCKSIZE If this is set, its value, rounded up to 512 or down to
a multiple of 512, will be used as the block size in
bytes by the --ll and --ss options. See _T_h_e _L_o_n_g _F_o_r_m_a_t
subsection for more information.
CLICOLOR Use ANSI color sequences to distinguish file types.
See LSCOLORS below. In addition to the file types
mentioned in the --FF option some extra attributes
(setuid bit set, etc.) are also displayed. The
colorization is dependent on a terminal type with the
proper termcap(5) capabilities. The default “cons25”
console has the proper capabilities, but to display the
colors in an xterm(1), for example, the TERM variable
must be set to “xterm-color”. Other terminal types may
require similar adjustments. Colorization is silently
disabled if the output is not directed to a terminal
unless the CLICOLOR_FORCE variable is defined or
----ccoolloorr is set to “always”.
CLICOLOR_FORCE Color sequences are normally disabled if the output is
not directed to a terminal. This can be overridden by
setting this variable. The TERM variable still needs
to reference a color capable terminal however otherwise
it is not possible to determine which color sequences
to use.
COLORTERM See description for CLICOLOR above.
COLUMNS If this variable contains a string representing a
decimal integer, it is used as the column position
width for displaying multiple-text-column output. The
llss utility calculates how many pathname text columns to
display based on the width provided. (See --CC and --xx.)
LANG The locale to use when determining the order of day and
month in the long --ll format output. See environ(7) for
more information.
LSCOLORS The value of this variable describes what color to use
for which attribute when colors are enabled with
CLICOLOR or COLORTERM. This string is a concatenation
of pairs of the format _f_b, where _f is the foreground
color and _b is the background color.
The color designators are as follows:
aa black
bb red
cc green
dd brown
ee blue
ff magenta
gg cyan
hh light grey
AA bold black, usually shows up as dark grey
BB bold red
CC bold green
DD bold brown, usually shows up as yellow
EE bold blue
FF bold magenta
GG bold cyan
HH bold light grey; looks like bright white
xx default foreground or background
Note that the above are standard ANSI colors. The
actual display may differ depending on the color
capabilities of the terminal in use.
The order of the attributes are as follows:
1. directory
2. symbolic link
3. socket
4. pipe
5. executable
6. block special
7. character special
8. executable with setuid bit set
9. executable with setgid bit set
10. directory writable to others, with sticky
bit
11. directory writable to others, without sticky
bit
The default is "exfxcxdxbxegedabagacad", i.e., blue
foreground and default background for regular
directories, black foreground and red background for
setuid executables, etc.
LS_COLWIDTHS If this variable is set, it is considered to be a
colon-delimited list of minimum column widths.
Unreasonable and insufficient widths are ignored (thus
zero signifies a dynamically sized column). Not all
columns have changeable widths. The fields are, in
order: inode, block count, number of links, user name,
group name, flags, file size, file name.
LS_SAMESORT If this variable is set, the --tt option sorts the names
of files with the same modification timestamp in the
same sense as the time sort. See the description of
the --tt option for more details.
TERM The CLICOLOR and COLORTERM functionality depends on a
terminal type with color capabilities.
TZ The timezone to use when displaying dates. See
environ(7) for more information.
EEXXIITT SSTTAATTUUSS
The llss utility exits 0 on success, and >0 if an error occurs.
EEXXAAMMPPLLEESS
List the contents of the current working directory in long format:
$ ls -l
In addition to listing the contents of the current working directory in
long format, show inode numbers, file flags (see chflags(1)), and suffix
each filename with a symbol representing its file type:
$ ls -lioF
List the files in _/_v_a_r_/_l_o_g, sorting the output such that the most recently
modified entries are printed first:
$ ls -lt /var/log
CCOOMMPPAATTIIBBIILLIITTYY
The group field is now automatically included in the long listing for files
in order to be compatible with the IEEE Std 1003.2 (“POSIX.2”)
specification.
LLEEGGAACCYY DDEESSCCRRIIPPTTIIOONN
In legacy mode, the --ff option does not turn on the --aa option and the --gg,
--nn, and --oo options do not turn on the --ll option.
Also, the --oo option causes the file flags to be included in a long (-l)
output; there is no --OO option.
When --HH is specified (and not overridden by --LL or --PP) and a file argument
is a symlink that resolves to a non-directory file, the output will reflect
the nature of the link, rather than that of the file. In legacy operation,
the output will describe the file.
For more information about legacy mode, see compat(5).
SSEEEE AALLSSOO
chflags(1), chmod(1), getfacl(1), sort(1), xterm(1), localeconv(3),
strftime(3), strmode(3), compat(5), termcap(5), sticky(7), symlink(7)
SSTTAANNDDAARRDDSS
With the exception of options --gg, --nn and --oo, the llss utility conforms to
IEEE Std 1003.1-2001 (“POSIX.1”) and IEEE Std 1003.1-2008 (“POSIX.1”). The
options --BB, --DD, --GG, --II, --TT, --UU, --WW, --ZZ, --bb, --hh, --ww, --yy and --, are non-
standard extensions.
The ACL support is compatible with IEEE Std 1003.2c (“POSIX.2c”) Draft 17
(withdrawn).
HHIISSTTOORRYY
An llss command appeared in Version 1 AT&T UNIX.
BBUUGGSS
To maintain backward compatibility, the relationships between the many
options are quite complex.
The exception mentioned in the --ss option description might be a feature
that was based on the fact that single-column output usually goes to
something other than a terminal. It is debatable whether this is a design
bug.
IEEE Std 1003.2 (“POSIX.2”) mandates opposite sort orders for files with
the same timestamp when sorting with the --tt option.
macOS 12.7 August 31, 2020 macOS 12.7
man
Manual pages are shown in the shell. Here are the essentials to navigate through contents presented in the pager:
d
- Scroll down half a pageu
- Scroll up half a pagej
/ k
- Scroll down or up a line. You can also use the arrow keys for thisq
- Quit/pattern
- Search for text provided as “pattern”n
- When searching, find the next occurrenceN
- When searching, find the previous occurrenceman
tricks are detailed in the help pages (hit “h” when you’re in the pager for an overview).RTFM!
Always check the documentation!
man
page explorer challengePartner up and choose a command from the list below. Use man
to complete these tasks:
You have about 5 minutes. Be ready to share your findings!
Reflection: How was using man
compared to online searches? How might you use it in future projects?
Key navigation commands are: - pwd
to print (the current) working directory. - cd
to change directory.
You can use absolute paths, but it’s better to use relative paths and invoke special symbols for a user’s home folder (~
), current directory (.
), and parent directory (..
) as needed
Let’s try it out!
Accessing the figures/
directory:
/Users/politicaltheory/Documents/github/qtm350/lectures/lecture-03/figures
Now, let’s go back to the previous directory:
/Users/politicaltheory/Documents/github/qtm350/lectures
Back two directories:
Beware of directory names that contain spaces. Say you have a directory called “My Documents”. (I’m looking at you, Windows.)
$ cd My Documents
work?$ cd "My Documents"
.$ cd My\ Documents
.assignment-05
or assignment_05
ls
(list): Show files and directories in the current directoryls -l
: Long listing format with detailed informationls -a
: Show hidden files (those starting with a dot)ls -lh
: Long listing format with human-readable sizesls -R
: List subdirectories recursivelypwd
(print working directory): Show the current directory pathcd
(change directory): Change the current working directorycd -
: Go back to the previous directory.
: Refers to the current directory..
: Refers to the parent directory~
: Refers to the home directorymkdir
: Create a new directorytouch
: Create a new empty file or update timestampscp
: Copy files or directoriesmv
: Move or rename files or directoriesrm
: Remove files (use with caution!)rmdir
: Remove empty directoriescat
: Display file contentsfind
: Search for files and directoriesFor a more detailed overview, click here
Follow these steps to practice using basic shell commands. Type each command and observe the results.
cd ~
mkdir practice && cd practice
touch file1.txt file2.txt
ls
mv file2.txt file3.txt
ls && cd ~
rm -r practice
ls
cd ~
mkdir shell-practice
cd shell-practice
touch file1.txt file2.txt file3.txt
ls
mkdir subdir
mv file2.txt subdir/
cp file1.txt file4.txt
ls -R
cd ..
rm -r shell-practice
ls
Bonus: Try using the man
command to learn more about any of the commands you’ve used.
pwd
, ls
, and cd
for file system navigation~
, .
, and ..
for directory navigation