Unix quicksheet

Unix Beginners QuickSheet stdin Standard in. This is the stream of data that a program recieves Quirks of the shell
Version: 0.10.0 from the command line. Not to be confused with command line • When you type a command in Unix the shell will set about finding
Date: 2/23/7 arguments that are specified when the program is run this is it. If you do not specify a path (such as /usr/bin/ls) but instead call
data that is recieved from user input or other commands while the command without a path (such as ls) the shell is responsible for
the program is running. Input can be sent from program to pro- finding it. To do this the shell uses a list of directories that it stores
This document is written for those who find themselves new to the Unix gram by piping it between the two using ones stdin and anothers in the $PATH variable. If the command you are trying to run is not in
command line (shell). Each Unix version has local variations in terms stdout. these directories it will not be found, even if it is in the directory you
of availible shells, commands, and directory layout. This is intended as are in. (It is considered bad practice to put the current directory (a ’.’)
a general guide only, verify these commands exist and are compatible stdout Standard out. This is the stream of data that (command line) in your $PATH to change this behavior.)
by refering to your local man page. programs print to the user interface. This output can be cap- • The shell has internal and external commands. Internal commands
Unix is a popular operating system that is built some of the most mature tured via a pipe or a redirect and sent to another program or are implemented by the shell itself. External commands are imple-
developments in operating system design. Many of the basic concepts file. stdout is know as file descriptor “1”. mented by other programs that exist as seperate programs (executa-
that are used today (and are covered in this guide) were designed over bles) on the system. Commands like ls are external. In the case of ls
30 years ago. An knowledge investment in Unix skills is likely to be environment This is the collection of variables and settings that a
program runs within. Each environment is inherited from the this command tends to be in /bin/ls. The cd command is an internal
a rewarding investment for a significant ammount of time. This gives shell command that is not found in the system but is interpreted by
the Unix user the oppurtunity to develop a deeper and more profound process that started it. Changes in your environment (such as
setting a variable) may be inherited by processes you start, but the shell itself as a request to change the current directory that it is
knowledge of their tool over the OS user who must re-learn the interface working in.
every major release. will not have an effect on processes that are allready running.
This is a key componet of a multi-user environment. • When a shell starts a command the relationship is called parent-child.
The naming is appropriate because the children inherit the environ-
Definitions ment of the parent (shell). This means that any variables or settings
The shell that were set in the shell environment become the settings for the child.
alias A command that is really another command or series of com- • The Unix shell is the primary method that users interact with the Changes made while in the child process do not change the environ-
mands. The command ll is frequently an alias for ls -l. system. It is the essence of the command line interface experience with ment of the parent. Variables that have been exported in the parent
Whenever you type an alias (such as ll) the shell substitutes the system. In the context of this paper, the shell is the essence of the are visible in the child. For this reason some programs will require that
the actual command ls -l. Unix experience. It is responsible for interpreting user requests entered a list of variables be set and exported prior to them running.
argument This is an additional parameter that follows the command on the command line and linking groups of commands together. • When a command is run from the shell it runs in the foreground.
on the command line that tells the command how you expect it • The shell is the interactive interface to the system that is utilized This means that all input and output are used for that command. If a
to behave. The parameter -l to the command ls tells ls that when running locally or when connecting remotely over a telnet or ssh command is backgrounded it will run in the background and you can
you want a long listing of directory items instead of the standard connection. continue to run additional commands in the foreground. A command
shortend list that you would get using only ls by itself. • The most common shells are bourne (sh), korn (ksh), C (csh), and can be backgrounded by calling it followed with a & character. Com-
bourne-again (bash). This document deals primarily with bourne and mands that require input should not be backgrounded.
daemon This is a program that runs in the background and handles its descendents (ksh and bash).
tasks and requests made to the system. Names of daemon pro- • Unix is case sensitive. The file wfavorite.txt is not the same as WFa-
cesses frequently end in the letter “d” by convention. One ex-
Understanding file attributes
vorite.txt. Unix views these as two different items. • All files belong to someone, and have descriptions of what kind of
ample of this is the httpd process that handles http requests.
files they are and how they can be used. This data is viewable with the
(The httpd daemon is more comonly known as a web server.) Shell shortcuts - file globbing ls command. Below is a sample listing created by running ls -l:
internal (command) Some commands are processed by the shell and • File globbing allows you list multiple files by expressing all the files -rw-rw-r-- 1 wfavorite devlopers 62896 Oct 4 08:26 hw.c
not by the local system. One such example is the cd command. as a pattern. The examples below use the echo to simply repeat the -rwxrwxr-x 1 wfavorite devlopers 4679 Oct 16 08:21 hw
If cd were a binary it would launch in its own environment, expanded glob. drwxrwxr-x 11 wfavorite devlopers 4096 Oct 15 08:15 work
change the directory and exit back to the original environment • The * character can match any number of characters. By itself the * From this we can determine that hw.c:
with the original directory. For this reason, commands that effect will match everything. The number of matches can be limited by using -rw-rw-r-- is a file
the environment, must be internal to the shell. These are also other characters with it. The ? character matches any single character. -rw-rw-r-- the owner can read, write, but not execute it
sometimes called builtins. These commands can be determined The ? by itself will match any single letter name. -rw-rw-r-- the group can read, write, but not execute it
with the type shell internal command. Print all files in the current directory that end in txt -rw-rw-r-- all others can only read it
link A link is a pointer to a file. It is frequently used to give a file echo *txt hw:
or directory multiple names. Links are either symbolic or hard. Print all files in the current directory that begin with “important” -rwxrwxr-x is also a file
Symbolic links are actually files that point to other files. Sym- echo important* -rwxrwxr-x both the user and group have read, write and execute
bolic links can refer to directories, work across filesystems, or Print all files in the current directory that have four characters -rwxrwxr-x others can only read, and execute it
refer to files that currently do not exist. Hard links are when a echo ???? work:
file has multiple different names. Use ln to create links. Print all files in the /usr/bin directory that begin with X drwxrwxr-x is a directory
echo /usr/bin/X* drwxrwxr-x shares the same permisssions as hw. Because a directory
pipe This is represented by the | character. When a pipe is placed be-
cannot be executed the execute permission means that
tween two commands it connects the output (stdout/stderr )of Shell advanced shortcuts users can enter the directory and view its contents.
the first command to the input (stdin) of the second command. • shell history is the ability to call upon and reuse previously run
This is the primary method of creating larger functionality by All of the above entries:
commands in the shell. The history can be viewed with the history
joining multiple smaller commands. are owned by user wfavorite and group devlopers.
shell command, or can be reused with one of the command line key
• File permissions are modified using the chmod command
process A program that has been read from disk and is running is called sequences. The previous command is typically available by using the
• File ownership is modified using the chown and chrgp commands
a process. Each process has a process identifier called a pid. A up arrow key. If this does not work -p (emacs mode) or -k (vi
list of processes and pids can be viewed with the ps command. mode) will recall the previous command. Useful Unix pointers
stderr Standard error. This is the stream of data that programs create • Most shells allow for a concept called command completion. This is • Don’t use spaces or strange characters in filenames. Because you
strictly for error messages. Frequently this is mixed with stdout often implemented as a (in bash shell), (korn emacs mode), have to refer to files on the command line it is best to not use spaces in
data and may seem identical. For most purposes stdout and or (korn vi mode) key sequence. Simply type the first string the file name. If you do use spaces it will be necessary to “quote” the
stedrr are identical, but the key difference is when used in long of characters in a filename and then hit the command completion name so that it does not appear as two different files when specified on
connections of commands the stderr can be isolated and sent to sequence, the shell will complete the file name from the possibilites it the command line.
a different location if necessary. stderr is known as file descriptor finds.
“2”.

Commands (grouped by task) ls Editors - Using vi
Commands to modify file attributes List names and attributes of files • More user friendly editors exist for Unix systems, but the vi editor
chmod chown ls -l can be found on virtually every Unix system you may ever encounter.
Commands to show info about files man View the online manual • vi has a command mode and an insert mode. Command mode is for
file ls View the manual page for the ls command telling vi things you want to do, such as open, save, edit a file, or quit.
Move, copy, or rename files man ls Insert mode is when you are actually typing text into the file.
mv cp ln cpio mkdir Create a directory • Some essential command mode commands:
Show contents of a text file Create a directory called mydir in the current working directory :w - Write the file
more cat head tail mkdir mydir :q - Quit the editor
Show what processes are running on a system more List the contents of a file (or stream of data) a bit at a time :q! - Quit the editor without saving changes you may have made
ps top Display the contents of a file called “largefile” i - Begin inserting text where the cursor is in the file
more largefile x - Delete the character under the cursor
Remote access Display the results of the ps command a page at a time dd - Delete entire line
• Remote access to Unix systems is typically gained in one of the fol- ps | more p - Paste previously deleted line
lowing ways: remote shell, file transfer, application access, or remote mv Move a file to a new location or name - (While in insert mode) will return you to command mode
console / X. Move “myfile” into the directory called “mydir” • The commands for vi and other editors are very rich. The full set of
• Remote shell is achived primarily by telnet or now, using the more mv myfile mydir commands is beyond the scope of this QuickSheet.
secure method, ssh. Rename “myfile” to “ourfile”
• Files are transfered individually by using ftp and rcp or the secure mv myfile ourfile Moving around the system - directories
equivelants sftp and scp. passwd Change your password on the system Directories are delimited with a / character.
ps List running proceses . referes to the current directory
Commands listed with examples List processes that you have running .. refers to the parent directory
cat concatenate and print files ps cd .. will move you to the parent directory
Dump /etc/hosts file to stdout List processes that belong to all users cd - will change to the previous directory
cat /etc/hosts ps ax (for OS X) ps -ef (for Linux, Solaris) pwd will print the current directory
Write everything typed (until -d is entered) to the file “newfile” pwd Print the current working directory
cat >> newfile rm Remove a file or directory Troubleshooting
cd Change (working) directories Remove a file called “myfile” • What shell am I running?
Change to the /usr/bin directory rm myfile echo $0 (echo $SHELL is not necessarily the one you are running )
cd /usr/bin Remove a direcotry called “mydir” • Why does my Backspace key print funny chars (like ^H)?
Change to your home directory rm -r mydir stty erase ^H (“stty erase ” then backspace key to define the
cd su Become another user backspace key)
Change back to the directory you were previously in Simply become the user fred (gain fred’s permissions) • Why does it say “file not found” when I run ./ls?
cd - su fred Because you said to run the copy of ls in the current directory and it
cp Copy a file or directory Become the user fred and run the login profile for that user does not exist there. Try: ls (If it does not work, you most likely have
Copy “myfile” to “myfile.backup” su - fred a problem with your PATH.
cp myfile myfile.backup Become the root user and run the profile (user environment) for root • Why can I only create a file 1 (or 2) gig in size?
Copy the directory “mydir” to “mydir.backup” su - Your account may have limits set. Check your ulimit for files using the
cp -r mydir mydir.backup sudo Run a command as another user (typically root) ulimit command.
cpio Copy a file or directory Edit the system hosts file
Note: Options to copi vary by system, check your local options. sudo vi /etc/hosts
Copy “sourcedir” to “destdir” Run the id command as root (worthless, but demonstrates sudo) Special files
cd sourcedir; find . -print -depth | cpio -pdm destdir sudo id • Some “files” on the system have special purposes. These files are
date Print the current date and time tail Print the last part of a file used by scripts and programs to generate or remove data. Some exam-
exit Log out from the current session Print the last (by default) 10 lines of “myfile.txt” ples are:
-d also works for this purpose tail myfile.txt /dev/null - Anything written to this file will disappear
file Determine what kind of file a target is top List the top (CPU) processes on a system /dev/zero - Anything read from this file will be all (binary) zeros
Determine what kind of file “myfile” is type Determine what a string / label is /dev/random - Anything read from this file will be random data
file myfile Determine if cd is a binary, alias, or internal command.
Determine what kind of file the (special) file “/dev/zero” is type cd (cd is an internal command / shell builtin) Additional help
file /dev/zero which Search your path for a binary Find all instances of “system” in the man files
find Locate a file in the system Show the full path to the ls command whatis system -or- apropos system
Find a file “myfile” in your home directory, print all matching names which ls Access the man(ual) page for the man browser
find ~/ -name myfile -print man man
grep Search through the contents of a file (or stream) for a pattern Piping and redirection
Look for a line with the word needle in the file called haystack.txt • Piping is typically done between programs while redirection is typically
grep needle haystack.txt done to or from files. Some examples are listed here. About this QuickSheet
Look for a line that contains only needle in haystack.txt To pipe the stdout and stderr of ls to sort Created by: William Favorite (wfavorite@tablespace.net)
grep "^needle$" haystack.txt ls | sort Updates at: http://www.tablespace.net
Look for the string “emacs” (a running process) in the output of ps Send the stdout of ls to sort and the stderr to the file /dev/null Disclaimer: This document is a guide and it includes no express war-
ps | grep emacs ls 2> /dev/null | sort ranties to the suitability, relevance, or compatibility of its contents with
head Print the first part of a file Send both the stdout and stderr of ls to the file /dev/null any specific system. Research any and all commands that you inflict
Print the first (by default) 10 lines of “myfile.txt” ls > /dev/null 2>&1 upon your command line.
head myfile.txt Overwrite the contents of file.txt with the output of ls Distribution: The PDF version is free to redistribute as long as credit
id Display current user and group membership ls > file.txt to the author and tablespace.net is retained in the printed and viewable
ls List all files in a directory Append the output of ls to the end of file.txt A
versions. LTEXsource not distributed at this time.
List file names ls >> file.txt

Unix quicksheet

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Unix quicksheet