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--- os_cp:intro [2023/03/01 11:38]
jkonczak [Autocompletion]
+++ os_cp:intro [2026/03/12 00:57] (current)
jkonczak [Glob names and wildcards]
@@ Line 22: / Line 22: @@
 POSIX - a standard (published by IEEE and The Open Group) for operating system interface and environment, predominantly built to unify Unix-like systems
-<html><small></html>
+<small>
-GNU/Linux
+Linux, GNU/Linux, Linux distribution…
   * [[https://www.gnu.org/gnu/gnu.html|GNU]] is a collection of free software that altogether forms an operating system supplied with a broad choice of user applications [[https://www.gnu.org/manual/blurbs.html]]
   * the kernel of GNU, [[https://www.gnu.org/software/hurd/|Hurd]], has never been fit enough for the task
   * therefore GNU software is usually run on top of Linux kernel
-  * most Linux distributions, apart form GNU software, has also a multitude of other software (not necessarely free or open source)
+  * most Linux distributions, apart form GNU software, has also a multitude of other software (not necessarily free or open source)
+  * some Linux distributions base on free and/or open source software that is neither GNU software nor uses GNU licenses
-<html></small></html>
+</small>
 ==== Shell and vital utilities ====
@@ Line 59: / Line 60: @@
   * Apple operating systems (e.g. MacOS) ship with modified BSD tools [[https://opensource.apple.com/releases/|[1]]] [[https://github.com/apple-oss-distributions/file_cmds|[2]]] [[https://github.com/apple-oss-distributions/text_cmds|[3]]]
   * Embedded / resource restrained systems often use [[https://www.busybox.net/downloads/BusyBox.html|BusyBox]]
-  * Android uses [[https://www.landley.net/toybox/|toybox]] [[https://cs.android.com/android/platform/superproject/+/master:external/toybox/toys/posix/|[4]]]
+  * Android uses [[https://www.landley.net/toybox/|toybox]] [[https://cs.android.com/android/platform/superproject/main/+/main:external/toybox/toys/posix/|[4]]]
   * For more, see [[https://wiki.archlinux.org/title/core_utilities]]
 <html></small></html>
-POSIX standarizes both the [[https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html|shell]]
+POSIX standarizes both the [[https://pubs.opengroup.org/onlinepubs/9799919799/utilities/V3_chap02.html|shell]]
-and its vital [[https://pubs.opengroup.org/onlinepubs/9699919799/utilities/contents.html|utilities]].
+and its vital [[https://pubs.opengroup.org/onlinepubs/9799919799/utilities/contents.html|utilities]].
 ==== Accessing the shell ====
@@ Line 78: / Line 79: @@
   * terminals bundled with some Linux desktop environment: [[https://docs.xfce.org/apps/terminal/start|xfce4-terminal]], [[https://en.wikipedia.org/wiki/GNOME_Terminal|GNOME Terminal]], [[https://konsole.kde.org/|konsole]]
   * default MacOS [[https://en.wikipedia.org/wiki/Terminal_(macOS)|Terminal]]
-  * drop-down terminals: [[https://apps.kde.org/yakuake/|yakuake]] / [[http://guake-project.org/|guake]] / [[https://github.com/lanoxx/tilda|tilda]]
+  * drop-down terminals: [[https://apps.kde.org/yakuake/|yakuake]] / [[https://guake.github.io/|guake]] / [[https://github.com/lanoxx/tilda|tilda]]
 <html></small></html>
@@ Line 98: / Line 99: @@
 where ''user'' is the user name and ''host'' is the name or address of the target device.
 \\
-For instance, if used ''john'' would like to log into a computer named ''polluks.cs.put.poznan.pl'', he would have to input \\ ''ssh john@polluks.cs.put.poznan.pl''.
+For instance, if the user ''john'' would like to log into a computer named ''polluks.cs.put.poznan.pl'', he would have to input \\ ''ssh john@polluks.cs.put.poznan.pl''.
+\\
+To terminate a ssh session, one can use either ''logout'' or ''exit'' command, or use //Ctrl// + //d// key combination on empty prompt line((//Ctrl// + //d// actually indicates //end-of-file// condition.)).
 Currently all major operating systems (including Windows) provide ''ssh'' command by default.
-<html><small></html>
+<small>
 Secure SHell encrypts all traffic. Its predecessor – telnet – sends all data (including passwords) in plaintext.
-<html></small></html>
+Upon password authentication, the client must send the password to the server.
+\\
+It is vital for security to confirm the authenticity of the server – the client
+must verify that it does not contact a rogue server that can learn the password
+([[https://docs.ssh-mitm.at/user_guide/authentication.html#id2|ready-to-go tool]])
+and/or hijack the session.
+\\
+[[https://en.wikipedia.org/wiki/Public-key_cryptography|Asymmetric cryptography]]
+is used to this end: the server has a (secret) private key, and upon each
+connection it sends the public key to the client, and the client verifies whether
+the public key pairs with the private.
+\\
+Hence, upon the first connection to a new server the SSH client program requests
+the  user to verify the authenticity of the public key and stores the key (in
+OpenSSH in ''~/.ssh/known_hosts'') to verify it automatically upon subsequent
+connections.
+</small>
 ~~Exercise.#~~ Run a terminal emulator. Execute command ''date'' and ''echo $SHELL'' within.
-~~Exercise.#~~ Execute command ''sleep 1h'' and interrupt it by pressing //Ctrl + c//.
+~~Exercise.#~~ Execute command ''sleep 1h'' and interrupt it by pressing //Ctrl + c//.
 ~~Exercise.#~~ Switch to second virtual console and log in. Execute ''pwgen''. Return to graphical console.
-~~Exercise.#~~ Use SSH to access ''polluks.cs.put.poznan.pl''.
+~~Exercise.#4~~a Use SSH to access your neighbour's computer.
+\\
+<small>~~Exercise.#4~~b Use SSH to access ''polluks.cs.put.poznan.pl''.</small>
 ===== Getting help =====
@@ Line 124: / Line 146: @@
 ~~Exercise.#~~ Display help for ''cat'' and ''bat'' commands by running them with help option. <html><small></html>(NB: ''bat'' is installed by default only in some Linux distros.)<html></small></html>
-Usually together with a program comes with a set of system manual pages. The pages can be displayed using the **''man //pagename//''** command. To leave the manual, type ''q''.
+Usually a program comes together with a set of system manual pages. The pages can be displayed using the **''man //pagename//''** command. To leave the manual, type ''q''.
 ~~Exercise.#~~ Display manual page for ''timeout'' command.
@@ Line 132: / Line 154: @@
 Page names are unique within a section, but there may be pages with the same name in different sections.
 \\
-You may use the **''whatis //pagename//''** command to learn which sections contain given page name and display the full page title.
+You may type **''whatis //pagename//''** or <small>''man -f //pagename//''</small> to learn which sections contain given page name and display the full page title.
 ~~Exercise.#~~ List all pages that are named ''time''.
-To select a page from a given section, one has to use ''man //section// //pagename//'' syntax.
+To select a page from a given section, one has to use ''man //section// //pagename//'' syntax, e.g., ''man 2 write''.
 ~~Exercise.#~~ The ''man'' itself is described on two manual pages. Display both. What information is contained in each one?
@@ Line 147: / Line 169: @@
 <html><small></html>
-For searching within manual there is also the ''apropos //what//'' command that searches within page names and titles.
+For searching within manual there are also the ''apropos //what//'' and ''man -k //what//'' commands that search within page names and titles.
 Apart from ''man'', there is an alternative (and less popular) documentation system called ''info''. To see an Info page, type ''info //name//''. Some programs ship with a more detailed Info document than manual page.
@@ Line 178: / Line 200: @@
 For instance, in ''find -amin N'' and ''find -anewer FILE'' the ''N'' and ''FILE'' are such placeholders: ''N'' must be replaced by number of minutes, and ''FILE'' must be replaced by a name of a file.
-~~Exercise.#~~ Run: \\ ''man zip'' and review the SYNOPSIS, \\ ''more --help'' and explain its syntax \\ ''taskset -h'' and explain its syntax
+~~Exercise.#~~ Run: \\ ''man zip'' and review the SYNOPSIS, \\ ''findmnt --help'' and explain its syntax \\ ''taskset -h'' and explain its syntax
 ==== Autocompletion ====
@@ Line 213: / Line 235: @@
 The command **''ls [//dir//]''** lists file in directory ''dir''. When run with no arguments, it lists the current working directory.
 \\
-By default ''ls'' does not list hidden files. The **''-a''** and ''--all'' switch changes this behaviour.
+By default ''ls'' does not list hidden files. The **''-a''** switch changes this behaviour.
 \\
-Switch **''-l''** / ''--list'' prints list of files with details such as file owner, size, modification date, etc.
+Switch **''-l''** prints list of files with details such as file owner, size, modification date, etc.
 ~~Exercise.#~~ List files in ''/usr/share/zoneinfo/'' and ''../../../../../bin''.
@@ Line 241: / Line 263: @@
 To change directory the command **''cd [//target//]''** is used. If no target is provided, ''cd'' changes current directory to the home directory.
 \\
-<html><small></html>If ''-'' is uses as the target, the directory is changed to the previously visited. <html></small></html>
+<html><small></html>If ''-'' is used as the target, the directory is changed to the previously visited. <html></small></html>
 ~~Exercise.#~~ Enter ''.config'' directory (located in your home directory) and list files within.
@@ Line 257: / Line 279: @@
 <html></small></html>
-==== Glob names and wildcards ====
+==== Wildcard, regex, … ====
-Upon parsing the user input, the shell attempts to replace any word containing wildcard characters **''*''**, **''?''** and expressions in square brackets **''[…]''**. A word that contains such wildcards is called [[https://en.wikipedia.org/wiki/Glob_(programming)|glob]].
-''*'' expands to any text, ''?'' expand to single character, ''[ace]'' expands to either ''a'', or ''c'', or ''e'', and ''[f-h]'' expands to either ''f'', or ''g'', or ''h''.
-If there is at least one file that matches the glob, the shell replaces the glob with all filenames that match. If no file matches, then the glob is left unaltered.
-~~Exercise.#~~ Change directory to ''/usr/bin/'' directory. List all files that end with ''cat''.
-~~Exercise.#~~ List all files that end with ''cat'' in ''/usr/bin/'' while being in your home directory.
-~~Exercise.#~~ List all files that are in the ''/usr/bin/'' directory that have names consisting of two chatacters.
-~~Exercise.#~~ List contents of ''/usr/share/zoneinfo/'' and its subdirectories using a single command.
-~~Exercise.#~~ List all files named ''UTC'' that are in any subdirectory of ''/usr/share/zoneinfo/''.
-~~Exercise.#~~ List all files starting with ''L'' that are in any subdirectory of ''/usr/share/zoneinfo/''.
-<html><small></html>
-~~Exercise.#~~ List all files starting with ''F'' or ''H''  that are in any subdirectory of ''/usr/share/zoneinfo/''. Use a single glob.
-~~Exercise.#~~ Navigate to ''/usr/bin'' and attempt to execute ''ls*''. What has happened?
-<html></small></html>
-==== Copying, moving and erasing files ====
-<html><small></html>
-To create an empty file, you can use ''touch //file//''. To create file with some contents, you can use ''echo //contents// > //file//''. The ''touch'' and ''echo'' commands as well as meaning of ''>'' will be explained later on.
-To display a file, use ''cat //filename//''.
-<html></small></html>
-=== Directories ===
+<small>
-**''mkdir //dir//''** creates a new directory.
+In computer science patterns/expressions that describe the expected data can be
+expressed and used to match against some data, usually to find fitting data or
+check if the data matches the description.
 \\
-<html><small></html>
+For instance, //lines beginning with a word followed by an equals sign// might
-''mkdir -p //dir1/dir2/dir3//'' creates directory ''dir1'', and directory ''dir2'' within ''dir1'', and ''dir3'' within ''dir1/dir2''.
+be written as a regular expression ''^\w+=''.
-With the ''-p'' switch ''mkdir'' does not print an error if a directory already exists.
-<html></small></html>
-To remove an empty directory one can use ''rmdir //dir//''.
+There are countless syntaxes and implementations of such patterns/expressions.
-~~Exercise.#~~ Create the following directory tree:
+In the shell, [[https://en.wikipedia.org/wiki/Wildcard_character|wildcards]]
-  .
+and [[https://en.wikipedia.org/wiki/Regular_expression|regular expressions]]
-  ├── foo
+are commonplace.
-  │   ├── baz
-  │   │   └── bar
-  │   └── bar
-  └── foobaz
-      └── bar
-~~Exercise.#~~ Remove ''foo/baz'' directory
-=== Hard and soft links ===
-Multiple directory entries can point to the same file. This is called a [[https://en.wikipedia.org/wiki/Hard_link|hard link]]. \\
-A directory entry can also point to another directory entry.  This is called a [[https://en.wikipedia.org/wiki/Symbolic_link|soft link or symbolic link]] (usually abbreviated as symlink).
-All Linux filesystems [[https://en.wikipedia.org/wiki/Comparison_of_file_systems#File_capabilities|support]] hard links for ordinary files, and soft links to arbitrary path (e.g., a file or a directory).
-To create a hard link, one can use **''ln //source// //destination//''**.\\
-To create a symlink, one can use **''ln -s //source// //destination//''**.
-~~Exercise.#~~ Create file ''file1'' with some contents. Create a hard link called ''file2'' of the file ''file1''. Modify ''file2''. Display ''file1''.
-<html><small></html>
-~~Exercise.#~~ The ''ls'' command can display for each file its link count. Discover how to do it.
-The disk space used by a file is reclamied once link count drops to 0 (all directory entries that link to the file are erased) and the file is no longer open in any process.
-<html></small></html>
-~~Exercise.#~~ Create in your home directory a symlink called ''TMP'' pointing to ''/tmp''. Change directory to ''TMP''. What does ''pwd'' output?
-~~Exercise.#~~ Create in your home directory a symlink called ''loop'' that points to your home directory. Enter it. And enter it again.
-~~Exercise.#~~ Create a symlink to a non-existent path. List the directory containing it.
-<html><small></html>
-The ''readlink [-f] //target//'' command resolves all symlinks and prints a [[https://en.wikipedia.org/wiki/Canonicalization|canonical]] path.
-The Windows NTFS filesystem supports links as well. Creating the links is possible e.g., with [[https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/mklink|mklink]] command.
-<html></small></html>
-=== Copying and moving files ===
-To copy files, one can use the **''cp''** command. To move (or rename) file, one can use the **''mv''** command.
-The basic syntax is ''cp/mv //source//… //destination//''. \\
-Multiple source files can be provided if the destination is a directory. \\
-If the destination is a file, it will be overwritten without warning <html><small></html>(unless ''-i'' or ''-n'' switch is used)<html></small></html>.
-<html><small></html>
-By default ''cp'' will deny copying a directory. Use ''-r'' to copy a directory recursively.
-<html></small></html>
-When ''cp'' copies a file, it creates a new file with current date, default permissions, etc.
+Syntax and implementation of both wildcards and regexes is language/application
+specific.
 \\
-To copy recursively, and preserve dates, permissions and more, one can use the **''-a''** switch (that stands for ''--archive'').
+The shell uses syntax summarized e.g., in
+''[[https://man7.org/linux/man-pages/man7/glob.7.html|man 7 glob]]'' and
+''[[https://man7.org/linux/man-pages/man7/regex.7.html|man 7 regex]]''
-<html><small></html>
+</small>
-With the ''-l'' switch ''cp'' creates a hard link instead of copying a file. Notice that this can be combined with ''--recursive''.
+==== Glob names and wildcards ====
-<html></small></html>
+Upon parsing the user input, the shell attempts to replace with filenames any
+word containing wildcard characters **''*''**, **''?''** and expressions in
+square brackets **''[…]''**. A word that contains such wildcards is called
+[[https://en.wikipedia.org/wiki/Glob_(programming)|glob]].
-~~Exercise.#~~ Copy, using a single command, the files ''/etc/os-release'' and ''/etc/SUSE-brand'' to the current working directory.
+''*'' expands to any text\\
+''?'' expand to single character\\
+''[ace]'' expands to either ''a'', or ''c'', or ''e'' \\
+''[f-h]'' expands to either ''f'', or ''g'', or ''h''
-~~Exercise.#~~ Run ''mkdir someDir && for F in file{1..3}; do echo $RANDOM$RANDOM > someDir/$F; done'' to create ''someDir'' directory with three files inside.
+If there is at least one file that matches the glob, the shell replaces the glob with all filenames that match. If no file matches, then the glob is left unaltered.
-~~Exercise.#~~ Copy the ''someDir'' directory recursively under a new name.
-~~Exercise.#~~ Move the newly copied directory into the ''someDir'' directory.
-~~Exercise.#~~ Rename ''someDir'' to a name of your choice.
+~~Exercise.#~~ Change directory to ''/usr/bin/'' directory. List all files that end with ''cat''.
-<html><small></html>
+~~Exercise.#~~ Change directory to your home directory. From there, list all files that end with ''cat'' in ''/usr/bin/''.
-~~Exercise.#~~ Copy the renamed directory with ''-al'' switches. Modify a selected file with any of the directories. Which files changed contents? <html><small></html> (You can ''cat //filename//'' or display modification dates with second accuracy using ''ls -l --time-style=+%H:%M:%S …'' or ''tree -D --timefmt=%H:%M:%S …'')<html></small></html>
+~~Exercise.#~~ List all files that are in the ''/usr/bin/'' directory that have names consisting of two characters.
-<html></small></html>
+~~Exercise.#~~ List contents of ''/usr/share/zoneinfo/'' and its subdirectories using a single command.
-=== Copying files to/from a remote machine ===
+~~Exercise.#~~ List all files named ''UTC'' that are in any subdirectory of ''/usr/share/zoneinfo/''.
-It is possible to copy files via SSH. Whenever one has SSH access to a remote machine, one can copy files with **''scp''** command. \\
+~~Exercise.#~~ List all files starting with ''L'' that are in any subdirectory of ''/usr/share/zoneinfo/''.
-''scp'' accepts ''//file//'' as file path on local machine and ''//user//@//host//://file//'' as a file path on a remote machine. Remote relative paths are relative to home directory.\\
-''scp'' accepts the ''-r'' switch for copying recursively.
 <html><small></html>
-Microsoft Windows now ships with ''scp'' command, but usually [[https://en.wikipedia.org/wiki/Comparison_of_FTP_client_software#Protocol_support|various file commanders]] are more convenient.
+~~Exercise.#~~ List all files starting with ''F'' or ''H''  that are in any subdirectory of ''/usr/share/zoneinfo/''. Use a single glob.
-<html></small></html>
+~~Exercise.#~~ Navigate to ''/usr/bin'' and attempt to execute ''ls*''. What has happened?
-Most SSH servers enable also the SFTP protocol that allows copying files more conveniently.\\
-**''sftp //user//@//host//''** launches sftp command line. You can use ''ls'' and ''cd'' to navigate the remote filesystem, and ''get'' and ''put'' to copy files. Type ''help'' to see all supported commands.
-~~Exercise.#~~ Create a file in ''/tmp'' directory in your computer. Copy the file to home directory of user ''student'' on another computer.
-~~Exercise.#~~ Copy the file to ''/tmp'' directory on another computer.
-~~Exercise.#~~ Copy the file to ''/tmp'' directory on another computer using ''sftp''.
-<html><small></html>
-=== Rsync ===
-The ''[[https://en.wikipedia.org/wiki/Rsync|rsync]]'' program is widely used to copy files and directories. It efficiently compares source files with destination files and copies only the differences. It can copy data to/from remote machines, and can compress the data sent via network to increase throughput. ''rsync'' is also commonly used to make backups.
 <html></small></html>
-=== Removing files ===
-The program that removes files is called **''rm''**.
-''rm'' by default won't remove directories (regardless if empty) and write-protected files.
-To remove a directory with ''rm'' (recursively with their contents) one has to add a ''-r'' switch.
-To remove write-protected files (and stop printing warnings whenever a file to be removed already does not exist) the switch ''-f'' (''--force'') can be used.
-A misused ''rm -rf …'' command is a notorious source of data loss. Beware especially of asterisk and what it expands to.
-''rm'' accepts **''-I''** and ''-i'' switches that ask for confirmation. ''-I'' asks once upon attempt to remove multiple files, and ''-i'' asks upon each file.
-~~Exercise.#~~ Create multiple files with ''touch file_{a..z}''. \\ Remove all files with a single ''rm'' command with 1) no switches 2) ''-f'' switch 3) ''-I'' switch 4) ''-i'' switch.
-~~Exercise.#~~ Repeat the remove command from the previous exercise when the files are gone. \\ Then repeat the command again with ''-f'' switch.
-~~Exercise.#~~ Create a directory and remove it with ''rm''.

Jan Kończak

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