Unix Command Review

Important UNIX conventions

1, Command Format

Commands must be typed all on one line, with spaces between the command, options, and arguments.

2,Naming Files

Filenames consist of alphanumeric characters, underscores, dashes, and periods.  DO NOT use spaces or other punctuation in filenames!

3,Case Sensitivity

Commands and filenames in UNIX are case sensitive!!

4,Filename Completiom

After typeing a unique prefix of a filename, pressing the Tab key will cause the Unix shell to complete the filename.

5,Command Editing

The up arrow key will retrieve a previous command. This command may be edited using the left/right arrow keys and backspace.

6,^C (control-C)

In UNIX, this terminates a currently running process when typed in the window the process is running in.

7,^Z (control-Z)

In UNIX, this sends a process to run in the background. The process will still exist; you just won't see it. Type "fg" to bring it back so that you can exit properly. Don't exit Unix with processes running in the background.

Working with Directories

0,Directory Notes

In UNIX pathnames, slashes (/) separate the directory and filenames
e.g. /home/mcb/myfile.txt  [ here home and mcb are directories and myfile.txt is a file ]. The current directory is referred to as . (‘dot’) and the parent directory is referred to as .. (‘dot dot’). The home directory is called ~ (‘tilde’).

1,Display present working directory

pwd   echo present working directory on screen

2,Change directory

cd dirname     Change current working directory to specific directory.

cd or cd ~    Go to your home directory, i.e. the directory you start in when you login.

cd ..   Go to the parent of the directory you are in now [ move up by 1 directory ]

3,Create/Delete directory

mkdir dirname     Creates a directory called dirname in the current directory

rmdir dirname     Delete (remove) empty directory

rm –r dirname     Delete directory and the content inside it(files,subdirectoris)

4,Lists directory contents

ls dirname    lists contents within specific directory

ls –l            shows a "long", detailed listing

ls –a            lists all of contents ,including hide directoris,files(starting with “.”)

Working with Files

1,Display file content

cat filename        display entire file

cat –vet              display file including Non-printing characters such as tab,carriage return,linefeed.It’s useful when a file move from windows to unix.

cat filename | less        display and navigate file content

2,Rename/Move files

mv file1 file2     rename file1 to file2

mv file dir          move the file to the specific directory

3,Copy a file

cp f1 f2      makes a copy of f1,named f2

cp f1 dir    copy f1 to a specific directory

4,Delete a file

rm f1         delete a file permanently,Use this command carefully - there is no Undo!!

rm –i f1    ask your confirm before you delete a file. in practice, you can add alias from rm to rm –i in your .bashrc file

5,Change file’s mode(who can operate on the file)

chmod perm f1  change mode of filename as specified by perm(issions). e.g. chmod  +x file makes file executable,chmod  g-r file removes group read permission on file

Patterns and Counting

1,Pattern

grep pattern files      find the lines that meet the pattern

grep –r pattern  dir   find the lines recursively in a directory. e.g. grep –r fatal  /var/log

2,Counting

wc –l       count by line,usually get input from pipeline. e.g. cat f1 | wc -l

wc –w       count by word

wc –m       count by character

Input/Output and Pipelines

0,Input/output notes

By default the output of a command goes to STDOUT (standard output or the monitor), and input of a command comes from STDIN (the keyboard).  Input and output can be redirected to/from files with the  < , > and  >> symbols

1,Redirect

cat f1 f2 > f3    concatenate files f1 and f2 and store the result in file f3. Warning: this overwrites file f3

cat f1 >> f2       concatenate file f1 and append to the contents of f2

sort < f1 > f1.sort    sort command reads from f1 and outputs to f1.sort

2,Pipelines notes

Multiple commands can be chained together in a pipeline with the | (‘pipe’) symbol.  When | is used between commands, the output of the first command is piped as input to the second command

3,Pipelines

grep “A” f1 | wc –l      find lines in f1 containing “A” and pipe them to wc  -l Note: this counts the number of lines containing “A”
grep “>” f1 | wc –l     note that quoting “>” prevents it from acting as output redirection.
cat f1|sort|head           send the contents of f1 to the sort command, then send the sorted lines to the head command to print the top 10.

Finding help

command –help   a short usage description

man command      manual for a command