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173 Cards in this Set
- Front
- Back
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Definition: Shell |
A program that takes keyboard commands and passes them to the operating system to carry out |
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Definition: Bash |
Bourne Again SHell, an enhanced replacement for sh (the original Unix shell program written by Steve Bourne) |
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Definition: Terminal Emulator |
Required to provide the graphical user interface with the capacity of interacting with the shell |
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Definition: Shell prompt |
Appears whenever the shell is ready to accept input |
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Tip: Shell Prompt - $ vs. # |
Seen as the last character of the shell prompt, # denotes that the terminal session has superuser privileges |
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Definition: Command history |
Pressing up-arrow key in the terminal will bring up the previously typed commands, generally up to 500 |
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Definition: Cursor |
Flashing character in the text, navigate using left and right arrow keys |
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Command: date |
Displays the current time and date |
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Command: cal |
By default, displays a calendar of the current month |
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Tip: How to copy and paste |
Left click mouse and drag through text, middle mouse button to paste |
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Command: df |
Shows the current amount of free space on your disk drives |
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Command: free |
Display the amount of free memory |
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Command: exit |
Ends a terminal session |
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Command: pwd |
Print name of the current working directory |
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Command: cd |
Change directory |
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Command: ls |
List directory contents |
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Definition: Hierarchical directory structure |
Organized in a tree like pattern of directories (folders in other systems) |
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Definition: Root directory |
First directory in the file system |
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Definition: Parent directory |
Directory above the current directory |
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Definition: Sub-directories |
Directories below the current directory |
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Definition: Absolute pathname |
Begins with the root directory and follows the tree, branch by branch, until the the desired directory or file is reached |
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Definition: Relative pathname |
Starts from the current working directory and leads to its destination |
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Relative Pathname: . |
Refers to the current working directory |
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Relative Pathname: .. |
Refers to the working directory's parent directory |
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cd - |
Changes to working directory to the previous working directory |
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cd ~username |
Changes to the home directory of the current user |
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Command: file |
Determine the file type |
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Command: less |
View file contents |
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ls: -a |
List all files, even hidden files (have a period at the beginning of the filename) |
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ls: -d |
See details about a directory |
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ls: -F |
Append an indicator character to the end of each listed name (such as a \ for directory) |
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ls: -h |
Display file sizes in human-readable format rather than in bytes |
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ls: -l |
Display results in long format |
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ls: -r |
Display results in reverse order |
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ls: -S |
Sort results by file size |
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ls: -t |
Sort results by modification time |
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less: b |
Scroll back one page |
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less: spacebar |
Scroll forward one page |
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less: up arrow key |
Scroll up one line |
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less: down arrow key |
Scroll down one line |
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less: G |
Move to the end of the text file |
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less: g |
Move to the beginning of the text file |
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less: \[characters] |
Search forward for the next occurrence of "characters" |
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less: n |
Search for the next occurrence of the previous search |
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less: h |
Display help screen |
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less: q |
Quit less |
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Directory: / |
Root directory |
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Directory: /bin |
Contains binaries (programs) that must be present for the system to boot and run |
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Directory: /boot |
Contains the Linux kernel, initial RAM disk image (for drivers needed at boot time), and the boot loader |
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Directory: /dev |
Contains device nodes, where the kernel maintains a list of all devices that it understands |
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Directory: /etc |
Contains all of the system-wide configuration files and shell scripts that start each of the system services at boot time |
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Directory: /home |
Directory that contains sub-directories for each user |
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Directory: /lib |
Contains shared library files used by the core system programs, similar to DLLs in Windows |
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Directory: /lost+found |
Each formatted partition using a Linux filesystem will have this directory, used in the case of a partial recovery from a filesystem corruption. Generally empty. |
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Directory: /media |
Contains the mount points for removable media that are mounted automatically on insertion |
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Directory: /mnt |
Contains mount points for removable media that have been mounted manually |
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Directory: /opt |
Used to install optional software, such as commercial products installed on a system |
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Directory: /proc |
Virtual filesystem maintained by the Linux kernel, contains readable files that give an understanding of how the kernel views your computer |
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Directory: /root |
Home directory for the root account |
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Directory: /sbin |
Contains system binaries, puritan's that perform vital system tasks that are generally reserved for the superuser |
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Directory: /tmp |
Storage for temporary files created by various programs |
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Directory: /usr |
Contains all the files and programs and support files used by regular users |
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Directory: /usr/bin |
Contains executable programs installed by your Linux distribution |
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Directory: /usr/lib |
The shared libraries for programs contained in /usr/bin |
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Directory: /usr/local |
Contains programs not installed by your distribution but are intended for system-wide use |
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Directory: /usr/sbin |
Contains more system administration programs |
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Directory: /usr/share |
Contains all the shared data used by programs in /usr/bin, such as icons, configuration files, system sound files, etc. |
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Directory: /usr/share/doc |
Contains documentation organized by package |
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Directory: /var |
Where data that is likely to change is stored |
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Directory: /var/log |
Contains log files of various system activities, especially /var/log/messages |
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Definition: Symbolic link |
File pointing to another file, similar to a shortcut. Often used in programming as the symbolic link can be replaced by a new symbolic link with the same name, but referencing a newer file version (e.g. foo -> foo 2.6, replaced by foo -> foo 2.7). Also called soft links and sym links. |
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Command: cp |
Copy files and directories, (e.g. cp item... directory) |
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Command: mv |
Move/rename files and directories, (e.g. mv item... directory) |
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Command: mkdir |
Create directories, (e.g. mkdir directory...) |
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Command: rm |
Remove files and directories, (e.g. rm item...) |
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Command: ln |
Create hard and symbolic links |
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Wildcard: * |
Any characters |
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Wildcard: ? |
Any single character |
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Wildcard: [characters] |
Any character that is a member of the set listed in characters |
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Wildcard: [!characters] |
Any characters that is not a member of the set of characters |
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Wildcard: [[:class:]] |
Any character that is a member of the specified class (almun, alpha, digit, lower, upper) |
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Long listing (1): -rw-r--r-- Example: -rw-r--r-- 1 root root 159744 2007-04-03 11:05 test.doc |
Access rights to the file. The first character indicates thetype of file. Among the different types, a leading dashmeans a regular file, while a “d” indicates a directory.The next three characters are the access rights for thefile's owner, the next three are for members of the file'sgroup, and the final three are for everyone else. |
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Long listing (2): 1 Example: -rw-r--r-- 1 root root 159744 2007-04-03 11:05 test.doc |
File's number of hard links. |
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Long listing (3): root Example: -rw-r--r-- 1 root root 159744 2007-04-03 11:05 test.doc |
The user name of the file's owner. |
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Long listing (4): root Example: -rw-r--r-- 1 root root 15974 2007-04-03 11:05 test.doc |
The name of the group which owns the file. |
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Long Listing (5): 15974 Example: -rw-r--r-- 1 root root 15974 2007-04-03 11:05 test.doc |
Size of the file in bytes. |
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Long Listing (6): 2007-04-03 11:05 Example: -rw-r--r-- 1 root root 15974 2007-04-03 11:05 test.doc |
Date and time of the file's last modification. |
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Long Listing (7): test.doc Example: -rw-r--r-- 1 root root 15974 2007-04-03 11:05 test.doc |
Name of the file. |
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cp: -a |
Copy the files and directories and all of their attributes,including ownerships and permissions. Normally,copies take on the default attributes of the userperforming the copy. |
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cp: -i |
Before overwriting an existing file, prompt the user forconfirmation. If this option is not specified, cp willsilently overwrite files. |
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cp: -r |
Recursively copy directories and their contents. Thisoption (or the -a option) is required when copyingdirectories. |
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cp: -u |
When copying files from one directory to another, onlycopy files that either don't exist, or are newer than theexisting corresponding files, in the destinationdirectory. |
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cp: -v |
Display informative messages as the copy isperformed. |
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mv: -i |
Before overwriting an existing file, prompt the user forconfirmation. If this option is not specified, mv willsilently overwrite files. |
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mv: -u |
When moving files from one directory to another, onlymove files that either don't exist, or are newer than theexisting corresponding files in the destinationdirectory. |
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mv: -v |
Display informative messages as the move is performed |
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rm: -i |
Before deleting an existing file, prompt the user forconfirmation. If this option is not specified, rm willsilently delete files. |
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rm: -r |
Recursively delete directories. This means that if adirectory being deleted has subdirectories, delete themtoo. To delete a directory, this option must bespecified. |
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rm: -f |
Ignore nonexistent files and do not prompt. Thisoverrides the -i option. |
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rm: -v |
Display informative messages as the deletion isperformed. |
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Tip: rm vs. trashcan |
Unix-like operating systems such as Linux do not have an undelete command.Once you delete something with rm, it's gone. Linux assumes you're smart andyou know what you're doing.Be particularly careful with wildcards. Example: Deleting all of the html files in a directory would be "rm *.html" However, "rm * .html" will delete all the files in the directory and then complain thatthere is no file called “.html”. With wildcards, you can also test the return with ls. |
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Hard Links |
Create an additional directory entry for a file Limitations 1. Cannot reference a file outside its own file system (not on the same disk partition as the link itself) 2. May not reference a directory. |
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Definition: Symbolic Links |
A special type of file that contains a text pointer to the referenced file ordirectory, similar to a Windows shortcut. A file pointed to by a symbolic link, and the symbolic link itself are largelyindistinguishable from one another, besides deletion. |
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Definition: Inode |
Numbered connection between data and name, hard links are additional names that refer to the same inode and therefore the same days. Shown with -i. |
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ls: -i |
Show inode number, generally -li and useful for hard links |
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ln: -s |
Create a symbolic link |
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Symbolic links: relative pathname vs absolute pathname |
Relative pathnames are preferred, as directories can be moved without breaking the link |
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Command: type |
Indicate how a command name is interpreted, (e.g. type [command]) |
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Definition: command |
1. An executable program, either compiled binaries (C and C++) or programs written in scripting languages (Perl, Python, Ruby, etc.) 2. Shell built-in 3. Shell function, miniature shell scripts incorporated into the environment 4. An alias, command we define built on other commands |
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Command: which |
Displays which executable program will be executed, used in the case where there is more than one version of an executable. Does not work for builtins or aliases, basically substitutes fire actual executables. |
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Command: help |
Provides info for shell builtins, (e.g. help [command]) |
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Command option: --help |
Many executables support this as an option to display a description of the commands supported syntax and options |
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Command: man |
Most executables include a formal piece of documentation, a manual |
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Tips: Man page organization |
1. User command 2. Programming interfaces fire kernel system calls 3. Programming interfaces to the C library 4. Special files such as device nodes and drivers 5. File formats 6. Games and amusements 8. System administration commands |
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Command: apropos |
Display a list of appropriate commands, based on a search term, (e.g. apropos floppy). Identical to man -k. |
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Command: info |
Display a command's info entry, GNU alternative to the man page for their programs that uses it's own reader program and includes hyperlinks (identified by leading asterisk, hover and press enter). |
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Command: whatis |
Displays a very brief description of a command, generally a one line-description of the man page, (e.g. whatis ls) |
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Command: alias |
Create an alias for a command, (e.g. alias name='string'). Using alias by itself will show you all of the current aliases. |
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Info: ? |
Display command help |
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Info: PgUp or Backspace |
Display previous page |
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Info: PgDn or Space |
Display next page |
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Info: n |
Display the next node |
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Info: p |
Display the previous node |
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Info: u |
Display the parent node of the currently displayed node |
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Info: Enter |
Follow the hyperlink at the cursor location |
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Info: q |
Quit |
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Definition: coreutils |
GNU project package of programs. Typing "info coreutils" will display a main page with hyperlinks |
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Tip: Product Documentation |
Many software packages installed on your system have documentation files residing in the usr/share/doc directory |
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Tip: .gz and zless |
.gz is a compressed gzip file. The gzip package includes a version of less called zless that with let you read gzip compressed text files. |
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Tip: Multiple commands |
It's possible to perform multiple commands in a row by separating each command with a semicolon, (e.g. command1; command2; command3; etc. or cd example; ls; cd -) |
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Tip: Check for used alias |
To see if an alias is already assigned, use the type command. |
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Command: unalias |
Remove an alias, (e.g. unalias foo) |
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Tip: Limitation of defining aliases on the command line |
Aliases will be erased when the terminal session is ended. To have them saved, you need to add the alias to the proper files. |
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Definition: I/O |
Input / Output |
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Command: cat |
Concatenate files, generally used for short text files or to join text files together (e.g. cat movie.mpeg.0* > movie.mpeg) |
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Command: sort |
Sort lines of text |
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Command: uniq |
Report or omit repeated lines |
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Command: grep |
Print lines matching a pattern |
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Command: wc |
Print newline, word, and byte counts for each file |
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Command: head |
Output the first part of a file; 10 lines by default, but can be adjusted with -n (e.g. head -n 5 ls-output.txt); Can also be used in pipelines |
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Command: tail |
Output the last part of a file; 10 lines by default, but can be adjusted with -n (e.g. tail -n 5 ls-output.txt); Can also be used in pipelines |
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Command: tee |
Read from standard input and write to standard output files, (e.g. "ls /usr/bin | tee ls.txt | grep zip" will output the entier listing to the ls.txt file before performing the grep filter) |
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Definition: standard ouput |
Results of the command line are sent to stdout. Generally not actually saved into a disk file; 1> |
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Definition: standard error |
Errors from the command line are sent to stderr. Generally not actually saved into a disk file; 2> |
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Definition: standard input |
stdin, is attached to the keyboard by default, and routed as input to certain programs; 0> |
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Definition: I/O redirection |
Allows the user to change where the output goes and where the input comes from. Normally, input comes from the keyboard and output goes to the screen. Basic redirection operator is ">", (e.g. ls -l /usr/bin > ls-output.txt) |
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Tip: Truncate a text file |
Using no command before the redirection operator (>) will empty a text file, (e.g. > ls-output.txt) |
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Redirection operator: > |
Overwrite/empty redirection operator |
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Redirection operator: >> |
Append redirection operator |
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Redirection operator: 2> |
Used for standard error (e.g. ls -l /bin/user/ 2> ls-error.txt) |
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Redirection operator: 2>&1 |
Added to the end of an output redirection to also redirect stderr to stdout, thereby capturing both (e.g. ls -l /bin/usr > ls-output.txt 2>&1). |
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Redirection operator: &> |
Modern way to redirect both stdout and stderr to the same file |
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Tip: How to redirect and hide unwanted output and errors |
Redirect to a bit bucket, which accepts input and does nothing with it; (e.g. ls -l /bin/usr 2> /dev/null) |
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Cat: ctrl+d |
Command to tell cat that it has reached the end of file (EoF) |
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Redirection operator: < |
Changes the source of stdin, (e.g. cat < lazy_dog.txt) |
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Pipe operator: | |
Causes the stdout of one command to be pipped into the stdin of another (e.g ls -l /usr/bin | less) |
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Filter: sort |
Sort (and combine if multiple directories) files (e.g. ls /bin /usr/bin | sort | less) |
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Filter: uniq |
Remove duplicates from the list, often used with sort, (e.g. ls /bin /usr/bin | sort | uniq | less) |
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uniq: -d |
Show only duplicate instances instead of unique instances, (e.g. ls /bin /usr/bin | sort | uniq -d | less) |
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Command: wc |
Word count displays the number of lines words and bytes contained in each file, (e.g. wc ls-output.txt) |
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wc: -l |
Only display line count, often used with sort to determine the number of individual items listed, (e.g. ls /bin /usr/bin | sort | uniq | wc -l) |
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Command: grep |
Used to find text patterns within files, (e.g. ls /bin /usr/bin | sort | uniq | grep zip) |
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grep: -i |
Ignore case |
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grep: -v |
only print lines without the pattern |
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head/tail: -n |
Adjust the number of lines to be output (e.g. -n 5) |
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Command: echo |
Display a line of text, causes the shell to print out its text arguments on standard output |
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Definition: Expansion |
The process that converts input into something that the shell can act upon (e.g. * is expanded to the files in the current working directory) |
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Definition: Pathname expansion |
The mechanism by which wildcards work |
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Tip: Pathname expansion of hidden files |
echo .* will show names with "." and ".." and since ".." refers to the relative pathnames of files in the parent directory, your result will be incorrect ls -d .[!.]?* would show any file starting with a ".", not followed by a subsequent ".", at least one other character, and finally followed by any number of characters |
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Definition: Tilde expansion |
Expands into the home directory of the named user or, if no name is specified, the current user |
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Definition: Arithmetic expansion |
The shell can perform arithmetic using expansion, $((expression)); only supports integers and allows for nesting; e.g. echo $(((5**2) * 3)) |
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Tip: Arithmetic expansion / vs % |
% is called the modulo, which will show remainders of division |
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Definition: Brace Expansion |
Allows you to create multiple text strings from a pattern containing braces Example: $ echo Front-{A,B,C}-Back Front-A-Back Front-B-Back Front-C-Back |
