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Terminal Basics

A beginner-friendly guide to the command line. What shells, terminals, and commands are, plus essential operations for navigating and managing files.

17 min read

The examples target Bash on GNUGNU's Not Unix/Linux unless stated otherwise. macOS uses BSDBerkeley Software Distribution versions of several utilities, and flags can differ. Replace angle-bracketed placeholders before running commands; quote paths containing spaces.

What is a command?

A command is a program that you can run from the terminal, it is also a utility of the shell, a shell function, or an alias. A command can receive arguments and options.

What is a shell?

A shell is a command line interpreter, it is a program that reads commands from the keyboard and executes them.

  • Bourne shell (sh)
  • Bash shell (bash)
  • C shell (csh)
  • Korn shell (ksh)
  • Z shell (zsh)
  • Fish shell (fish)
  • PowerShell (powershell)

What is a terminal?

A terminal emulator provides a text interface to a shell or another program. It often runs inside a graphical desktop window; the shell is the command interpreter running within it.

Commands

ls

  • ls -al : list files in long format, including hidden files
  • ls -lrt : list files in long format, sorted by modification time, oldest first
  • ls -lh : list files in long format, with human readable sizes

tree : list files in a tree format

  • tree -L 2 : list files in a tree format, 2 levels deep.

cd [path]

  • cd : move to home directory
  • cd -: change directory to previous directory
  • cd .. : change directory to parent directory
  • cd / : change directory to root directory
  • cd <path>: change directory to the specified path
  • cd ~<user>: change directory to user’s home directory
  • cd ~: change directory to current user’s home directory

pwd (print working directory)

  • pwd

managing files

touch

  • touch file_name: create an empty file if absent; otherwise update its timestamps.
  • touch file_1_name file_2_name : create file1 and file2
  • > file_name : create an empty file or truncate an existing file to zero bytes

cp

  • cp file_name file_name_copy: copy file_name to file_name_copy.
  • cp -r dir_name dir_name_copy: copy dir_name to dir_name_copy.
  • cp -p : copy files preserving attributes
  • cp -a : copy files preserving attributes and links
  • cp -i : prompt before overwriting existing files
  • cp -f : force overwrite existing files

mv

  • mv <file_name> <path> : move file to specified path

  • mv <file1> <file2> : rename file1 to file2

  • mv -i : prompt before overwriting existing files

  • mv -f : force overwrite existing files

  • mv <dir1> <path>: move dir1 to specified path

  • To include hidden entries in Bash, use dotglob and nullglob, then pass the expanded array to mv. The destination must be outside the source:

    (
  shopt -s dotglob nullglob
  files=(source_dir/*)
  if ((${#files[@]})); then
    mv -- "${files[@]}" destination_dir/
  fi
)

mkdir

  • mkdir <dir_name>: create dir_name directory.
  • mkdir <dir1> <dir2> <dir3> : create directories dir1, dir2, dir3
  • mkdir -p : create parent directories as needed

cat head tail less

  • cat <file_name>: print file_name contents.
  • cat > <file_name> : create file and write to it.
  • cat <file_name1> <file_name2> : print file1 and file2 contents.
  • head <file_name>: print the first 10 lines of file_name.
  • head -n 20 <file_name>: print the first 20 lines of file_name.
  • tail <file_name>: print the last 10 lines of file_name.
  • tail -n 20 <file_name>: print the last 20 lines of file_name.
  • less <file_name>: print file_name contents in less.
  • less +20 <file_name>: print file_name contents in less starting at line 20.
  • less +/text <file_name>: print file_name contents in less starting at the first occurrence of text.
  • less -N <file_name>: print file_name contents in less with line numbers.
  • less -S <file_name>: print file_name contents in less without wrapping lines.
  • less -F <file_name>: exit automatically if the contents fit on one screen.
  • less -R <file_name>: display supported color escape sequences.
  • less -X <file_name>: skip terminal initialization/deinitialization sequences.
  • less -Q <file_name>: suppress the terminal bell.
  • less -K <file_name>: exit on an interrupt, such as Ctrl-C.
  • less -M <file_name>: use a more detailed prompt.
  • less -i <file_name>: case-insensitive search unless the pattern has uppercase letters.
  • less -I <file_name>: always ignore case in searches.
  • less -I -N -S <file_name>: combine case-insensitive search, line numbers and unwrapped lines.

less

  • less file_name: print file contents, one page at a time.
    • /word_to_search_for : allow you to search for a word in the file.
    • q : quit.

file

  • file <path> : print file type

rm

  • rm <file_name>: delete file_name.
  • rm -i <file> : prompt before removing a file
  • rm -f <file> : remove without prompting; ignore missing files
  • rm -r <dir> : remove directories recursively
  • rmdir <dir_name>: remove an empty directory.
  • rm -rf <dir_name>: delete dir_name and its contents.

xdg-open / open

  • xdg-open file_name: open with the default desktop application on Linux.
  • open file_name: use the default application on macOS.

nautilus

  • nautilus [path_to_folder] : open file manager

type

  • type command: print command type

alias

  • alias: list aliases
  • alias foo="bar": create alias foo for bar

help

In Bash, help is a built-in that documents Bash built-ins; it does not provide the manual for arbitrary external programs.

  • help command: print command help

man

user manual for commands

  • man command: print command manual

info

  • info command: print command info

whatis

  • whatis command: print command description

wildcards

Allows us to match patterns in filenames.

  • *: matches any number of characters.
  • ls *.txt: matches any file with .txt extension.
  • ls data*.txt: list files with .txt extension starting with data.
  • ?: matches any single character.
  • ??: matches any two characters and so on.
  • ls data?.txt: list files with .txt extension starting with data and a single character.
  • [abc]: matches a, b, or c.
  • [!abc]: matches anything but a, b, or c.
  • ls [[:upper:]]*: list matching uppercase-leading names; for matching directories, ls lists their contents unless -d is used.
  • ls -d [[:upper:]]*/: list matching directories starting with an uppercase letter.
  • ls -d [[:lower:]]*/: list matching directories starting with a lowercase letter.
  • ls [ad]*: list files starting with a or d followed by any number of characters.
  • ls -l [2-9]*: list files starting with a number between 2 and 9.
  • ls -l [0-9][0-9]*: list files starting with two numbers.

redirection

A redirection is a way to redirect the output of a command to a file or another command. file descriptorA small number that a process uses to refer to an open file or stream. (0-1-2).

  • standard input (stdin) : 0
  • standard output (stdout) : 1
  • standard error (stderr) : 2
  • command < file_name: read from file.
  • command > file_name: write stdout of the specified command to file.
  • command >> file.txt : append stdout to file.
  • ls 2> file_name: write stderr to file.
  • ls 2>> file_name: append standard error to file.
  • ls > file_name 2>&1: write standard output and standard error to file.

pipes

A pipe is a way to connect the output of one command to the input of another command.

  • echo "foo" | grep "foo": print “foo” and grep for “foo”.
  • cat file1 file2 | grep "foo": print file1 and file2 and grep for “foo”.
  • ls -lh | tee file_name | less: list files in long format with human readable sizes, write to file, and print one page at a time.
  • ls -lh folder | sort | tee file_name | less: list files in long format with human readable sizes, sort, write to file, and print one page at a time.
  • cowsay "foo" | lolcat: print “foo” with cowsay and lolcat.
  • echo "foo" | cowsay | lolcat: print “foo” with cowsay and lolcat.

control operators

Control operators determine sequencing and conditions. ;, &&, and || do not by themselves create subshellsA child copy of the shell that runs commands in a separate process.; & starts an asynchronous job in Bash.

  • ls; echo "foo": list files and print “foo”.
  • ls; mkdir dir; cal: list files, create directory, and print calendar. (asynchronous ”&” creates a background process).
  • ls & echo "foo": run ls in the background and echo in the foreground.
  • ls && echo "foo": list files and print “foo” if ls succeeds.
  • ls || echo "foo": list files and print “foo” if ls fails.

permissions

A permission is a way to control access to a file or directory.

ls -l begins with a type character: - for a regular file, d for a directory, l for a symbolic linkA file that points to another path, like a shortcut., and b for a block device. A block device is a device that is accessed in fixed-size blocks.

Kind of permissions

  • r : read
  • w : write
  • x : execute
ownergroupother
rwxr-xr-x
111101101
755

Symbolic mode

u : user g : group o : other a : all chmod u=rwx,g=rwx,o=rwx file : set permissions to 777

  • root user: a root user has full access to the system.
  • chmod : change file permissions (change mode)(octal).
  • chmod 755 file_name: set permissions to 755. (owner: rwx, group: rx, other: rx).
  • chmod u=rwx,g=rwx,o=rwx file_name: set permissions to 777. (owner: rwx, group: rwx, other: rwx).
  • chmod u-rwx,g-rwx,o-rwx file_name: set permissions to 000. (owner: ---, group: ---, other: ---).
  • chmod g+w file_name: add group write permission, preserving all other bits.
  • whoami: print current user.
  • id: print current user and group.
  • su root: switch to root user.
  • su user: switch to user.
  • in ubuntu: sudo su :switch to root user.
  • passwd: change password.
  • chown -R "$(id -un):$(id -gn)" folder_name: recursively set owner and primary group to the current user; sufficient privileges are required.

change password

passwd : change password

managing permissions

  • chmod u=rwx,g=rwx,o=rwx file_name: set permissions to 777
  • chmod u=rwx,g=rwx,o=rx file_name: set permissions to 775
  • chmod u=rwx,g=rwx,o= file_name: set permissions to 770
  • chmod u=rwx,g=rwx file_name: set user and group to rwx; leave other bits unchanged
  • chmod u=rwx,go=w file_name: set ordinary permission bits to 722
  • chmod 777 file_name: change file_name permissions to 777.
  • chmod 755 file_name: change file_name permissions to 755.
  • chmod 644 file_name: change file_name permissions to 644.
  • chmod 600 file_name: change file_name permissions to 600.
  • chmod 400 file_name: change file_name permissions to 400.
  • chmod 000 file_name: change file_name permissions to 000.
  • chmod u+x file_name: add execute permission to file_name for user.
  • chmod u-x file_name: remove execute permission to file_name for user.
  • chmod u+r file_name: add read permission to file_name for user.
  • chmod u-r file_name: remove read permission to file_name for user.
  • chmod u+w file_name: add write permission to file_name for user.
  • chmod u-w file_name: remove write permission to file_name for user.
  • chmod u+x,g+x,o+x file_name: add execute permission to file_name for user, group and others.
  • chmod u-x,g-x,o-x file_name: remove execute permission to file_name for user, group and others.
  • chmod u+r,g+r,o+r file_name: add read permission to file_name for user, group and others.
  • chmod u-r,g-r,o-r file_name: remove read permission to file_name for user, group and others.
  • chmod u+w,g+w,o+w file_name: add write permission to file_name for user, group and others.
  • chmod u-w,g-w,o-w file_name: remove write permission to file_name for user, group and others.
  • chmod u+x,g+x,o+x,u-r,g-r,o-r,u-w,g-w,o-w file_name: add execute permission to file_name for user, group and others and remove read and write permission to file_name for user, group and others.

environment variables

Environment variables are name/value pairs inherited by child processes. In Bash, assignment creates a shell variable; export makes it part of the environment passed to subsequent commands.

  • ln -s /home/user/dir link_name: create symbolic link to dir named link_name.
  • printenv: print environment variables
  • echo $VARIABLE_NAME: print VARIABLE_NAME environment variable
  • echo $PATH: /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin: /sbin:/bin:/usr/games:/usr/local/games:/snap/bin —> the directories where the shell looks for commands
  • echo $HOME: print HOME environment variable — /home/user — the home directory of the current user
  • echo $USER : print USER environment variable — user — the current user
  • echo $SHELL : print SHELL environment variable — /bin/bash — the shell program

how to modify environment variables?

export PATH=$PATH:/home/user/bin: add /home/user/bin to PATH environment variable

  • look for the file .bashrc (bash) in the home directory of the user.
  • open the file .bashrc with a text editor to who is using bash. In mac .zshrc. That’s could vary depending on the shell you are using.
  • add the line export PATH=$PATH:/home/user/bin to the file .bashrc.
  • to add a environment variable, add the line export VARIABLE_NAME='value' to the file .bashrc.
  • to add an alias, add the line alias alias_name='command' to the file .bashrc.
  • to add bins to the path, add the line export PATH=$PATH:/home/user/bin to the file .bashrc.
  • save the file .bashrc.

Searching command

A search command is a way to search for a command.

  • which <command> : print command path. If the command is not found, nothing is printed.
  • which code: /usr/bin/code —> the path to the command code
  • find path -name "file_name": search for file_name in path. segment by name (wildcards and find):
  • find path -name "*.txt": search for files with .txt extension in current directory. segment by type:
  • find path -type f -name "*.txt" : search for files with .txt extension in the specified path.
  • find ./ -type f -name "*.log": search for files with .log extension in current directory.
  • find ./ -type d -name dir: search for directories with name dir in current directory.
  • find ./ -type d -empty: search for empty directories in current directory.
  • find ./ -maxdepth 2 -type d: search for directories in current directory with a maximum depth of 2
  • find ./ -mindepth 2 -type d: search for directories in current directory with a minimum depth of 2 segment by size:
  • find ./ -type f -size +100k: search for files in current directory with a size greater than 100k.
  • find ./ -size +100M: search for files larger than 100M in current directory.
  • find ./ | less: search for files in current directory and print the results in less. segment by date:
  • find ./ -type f -mtime +1: search for files in current directory that were modified at least two full 24-hour periods ago (-mtime rounds down). segment by permission:
  • find ./ -type f -perm 777: search for files in current directory with permissions 777.
  • find ./ -type f -perm -777: search for files in current directory with all of the listed permission bits set (additional special bits may be set).
  • find ./ -type f -perm /777: search for files in current directory with at least one listed permission bit set (GNU find syntax). segment by owner:
  • find ./ -type f -user user: search for files in current directory with owner user.
  • find ./ -type f -group group: search for files in current directory with group group. segment by content:
  • find ./ -type f -exec grep -l 'text' {} \;: search for files in current directory with the text text and print the file name.
  • find ./ -type f -exec grep -q 'text' {} \; -ok rm {} \;: find matching files and ask before deleting each; this preserves filenames containing spaces.
  • find ./ -type f -size +100k -exec rm {} \;: search for files in current directory with a size greater than 100k and delete them.

managing directories

A directory is a way to manage directories.

  • pwd: print working directory.
  • cd dir_name: change directory to dir_name.
  • cd ..: change directory to parent directory.
  • cd ~: change directory to home directory.
  • cd -: change directory to previous directory.
  • ls: list directory contents.
  • ls -a: list directory contents including hidden files.
  • ls -l: list directory contents in long format.
  • ls -la: list directory contents in long format including hidden files.
  • ls -lh: list directory contents in long format with human readable sizes.
  • ls -lah: list directory contents in long format with human readable sizes including hidden files.
  • ls -lt: list directory contents in long format sorted by modification time.
  • ls -lat: list directory contents in long format sorted by modification time including hidden files.
  • ls -lS: list directory contents in long format sorted by size.
  • ls -lSr: list directory contents in long format sorted by size in reverse.
  • ls -lX: list directory contents in long format sorted by extension.
  • ls -lXr: list directory contents in long format sorted by extension in reverse.
  • GNU ls -lU: use directory order, without sorting. On macOS, -U has different timestamp semantics; check the local man ls.
  • ls -lF: list directory contents in long format with a slash after directories.

whereis

whereis locates binaries, manual pages and source locations for command names; it is not a general file search.

  • whereis <file_name>: find file_name.
  • whereis -b <file_name>: find file_name binaries.
  • whereis -m <file_name>: find file_name manuals.
  • whereis -s <file_name>: find file_name sources.

ln

ln -s : create symbolic links

find

Quote patterns so find, rather than the shell, interprets them:

find . -type f -name '*.txt'
find . -type f -name '*.txt' -exec grep -n 'foo' {} +

The first command finds text files recursively. The second searches their contents and safely handles filenames containing spaces. Permission predicates are bit tests, not numeric comparisons; see the GNU find mode-bit referencegnu.orgGNU find manual, at the section on file mode bits: how -perm and -chmod read permission bits..

grep

A grep is a way to search for a pattern in a file.

  • grep <regex> <file_name>: search for regex in file_name.
  • grep -r <regex> <file_name>: search for regex in file_name recursively.
  • grep -i <regex> <file_name>: search for “foo” in files, case insensitive.
  • grep -v <regex> <file_name> : invert match, print non-matching lines.
  • grep -l <regex> <file_name>: print names of files with at least one matching line
  • grep -c <regex> <file_name>: count matching lines, not individual occurrences.
  • grep -n <regex> <file_name>: print line numbers.
  • grep -A 2 <regex> <file_name>: search for regex in files, print 2 lines after match
  • grep -B 2 <regex> <file_name>: search for regex in files, print 2 lines before match
  • grep -C 2 <regex> <file_name>: search for regex in files, print 2 lines before and after match
  • wc <file_name>: count newline characters, words and bytes.
  • wc -l <file_name>: count lines in file_name.
  • wc -w <file_name>: count words in file_name.
  • wc -c <file_name>: count bytes. Use wc -m to count characters.

Network utilities

These commands inspect interfaces or communicate with network services.

  • ifconfig: print network interfaces.
  • ping <host-or-ip>: send ICMPInternet Control Message Protocol echo requests; a missing reply can reflect filtering
  • curl <url>: print url contents.
  • curl <url> > index.html: write url contents (stdout) to index.html.
  • wget <url>: download url. get form url.
  • traceroute <host-or-ip>: probe hops toward a destination; some may not reply.
  • netstat -tulpn: print listening ports.
  • netstat -i: print networks interfaces.

compression

A compression is a way to compress files.

  • gzip <file_name>: compress a regular file; use tar with gzip for a directory tree.
  • tar -cvf <file_name.tar> <file_name/dir>: create tar file.
  • tar -cvzf <file_name.tar.gz> <file_name/dir>: create tar.gz file (gzip).
  • tar -xvzf <file_name.tar.gz>: extract tar file.
  • zip -r <file_name.zip> <file/dir>: create zip file.
  • unzip <file_name.zip> : extract zip file.

Process management

A process is a running instance of a program.

  • ps: show processes associated with the current terminal by default.
  • ps -ef: show a broader process listing on common Unix systems.
  • kill <pid>: send SIGTERMThe termination signal: it asks a process to exit, and the process may catch or ignore it., requesting termination; it is not guaranteed to stop the process.
  • top: inspect processes interactively; keys vary by platform. Read its help or man top.
  • htop: an optional interactive terminal process viewer.

Background jobs

Bash job control manages commands started in the current interactive shell:

  • sleep 1000 &: start a background job.
  • jobs: list this shell’s jobs.
  • Ctrl-Z: suspend the foreground job, rather than terminate it.
  • bg %1: continue job 1 in the background.
  • fg %1: continue job 1 in the foreground.
  • kill %1: send SIGTERM to job 1.
  • kill %%: signal the current job, not all background jobs.

A background command that tries to read from the terminal normally stops with SIGTTINThe signal sent to a background job that reads from the terminal; by default it stops the job.. Use input from a file or run it in the foreground instead.

vim

  • vim <file_name>: open file_name.
    • i: insert mode.
    • esc: normal mode.
    • :w: write file.
    • :q: quit file.
    • :wq: write and quit file.
    • :q!: quit without saving.
    • :w!: write over file.
    • :wq!: write over file and quit.
    • :w <file_name>: write to file_name.
    • /regex: search for regex.
    • dd: delete line.
    • yy: copy line.
    • p: paste line.
    • u: undo.
    • ctrl + r: redo.
    • gg: go to first line.
    • G: go to last line.
    • n: next match.
    • N: previous match.
    • :%s/foo/bar/g: replace every match of foo with bar throughout the buffer.
  • vim -R <file_name>: open file_name in read-only mode.
  • vim -O file1 file2: open files in vertical splits.
  • vim -o <file_name>: open file_name in horizontal split mode.
  • vim -p <file_name>: open file_name in tab mode.
  • vim -c <command>: execute command.
  • vim -c "set number" <file_name>: open file_name with line numbers.
  • vim -c "set number" -c "set hlsearch" <file_name>: open file_name with line numbers and highlight search.

customize the terminal

  • bashohmybash.github.ioOh My Bash, an open source framework of themes, plugins and aliases for Bash.
  • zshohmyz.shOh My Zsh, an open source framework of themes and plugins for configuring Zsh.

References