Lệnh cơ bản

Listing and Moving Files and Directories

ls – LiSt files – “-a” lists all files, “-l” give a long DOS-dir-like output – example: “ls -la”

cp – CoPy – copy file(s) from one location to another – example: “cp *.c another_directory/”

mv – MoVe – move file(s) from one location to another, same as cp except it removes files afterwards

rm – ReMove – delete files – example: “rm *.o”

cd – Change Directory – example “cd /tmp”

mkdir, rmdir – MaKe DIRectory and ReMove DIRectory

ln – LiNk – make a link to a file – two types of links, normal and symbolic – example: “ln -s original newlink”

Special Directories – ‘.’ is current, ‘..’ is current’s parent, ‘~’ is home, and ‘/’ is the root (or top) of all directories

Redirection and Shell Stuff

| – Pipe, one of UNIX’s best features, used to send output from one program to be input to another – example: “ls -l | grep uzi”

>, >>, < – Redirect output of a program to a file, append output to end of a file, and get input from a file – example: “./a.out < input > ouput”

*, ? – Wildcards – used to specify any number (including zero) of any character for ‘*’, and any one character for ‘?’ – example: “ls *.?”

$var – An environment variable, where “var” is the name and a value can be seen using “echo $var”

set, setenv – used to set environment varibles, depending on shells.

Managing File Permissions

Sample “ls -l /bin/ls” output: -rwxr-xr-x 1 root root 29980 Apr 23 1998 /bin/ls
– First ten characters are the file’s permissions. First is file type, ‘-‘ for normal, ‘d’ for directory, ‘l’ for symlink, etc.
– Three sets of three characters of “rwx”, or Read, Write, Execute permission – first for owner, then group owner, then everyone.
– Then we have number of links to file, owner of the file, group owner of file, file size, date it was last modified, and the file’s name.

chmod – Change a file’s mode or permissions – one way is to use octal numbering – example: “chmod 751 /bin/ls” for rwxr-x–x

chgrp – Change a file’s group – example: “chgrp users /bin/ls”

chown – Change a file’s owner – example: “chown uzi /bin/ls”

umask – Set default file permissions (generally, do the opposite, or “777 minus what you want”)

Process Management

ps – Get a listing of running “processes” or programs – example: “ps -aux”

kill – Kill a running process – example: “kill -CODE PID”, where CODE is an optional kill code, and PID is the process ID #.

& – Run a program in the background – example “netscape &”

CTRL-Z – Suspend a running program

CTRL-C – Kill a running program

fg, bg – Put a suspended program in the foreground or background

jobs – List running programs of this terminal – each has a number that can be refered to as %#, or %1 for number one (useful with fg, bg and kill)

nice – Make a program use less computer time

nohup – Let a program run after you log out (NO Hang-UP)

Viewing Text Files

cat – Concatinate and display files, used to output a file’s contents without pausing – example: “cat textfile”

more – Like cat, but pauses every screen-full – example: “more prog.c”

less – Like more, but more powerful

head, tail – View the beginning or ending of a file, given a number option with display that many lines – example: “tail -25 /var/spool/mail/uzi”

wc – Get statistics of how many lines, words and characters in a file – example: “wc file.txt”

Searching and Comparing

find – Find a file, second argument is where to search from – example: “find . -name ‘*.c’ -print”

grep – Look for text in a file – example: “grep variable *.c”

cmp – Compare two files – example: “cmp file1 file2”

diff – Output difference between two files – example: “diff prog.c.orig prog.c > prog.c.diff”

Printing – Depending on which Unix you’re using (BSD type, SYSV type) is which you may be using

lpr, lp – Print a file -examples: “lpr -P printer file” or “lp -d printer file”

lpq, lpstat – Get statistics on a printer(s)

lprm, cancel – Cancel a print job

Finding and Communicating with other Users

finger – Get information on another user on the system – example: “finger uzi”

w, who – Find out who else is on a system

write – Write a message to a user (user CTRL-D to stop) – example: “write uzi”

talk – Talk to a user (CTRL-C to stop, and there’s also “ytalk” which is an enhanced version) – example: “talk uzi”

mesg – Use “mesg y” or “mesg n” to allow or disallow others to write and talk to you

Remote Commands

telnet – Open a connection on another system – example: “telnet fire.csua.ucla.edu”

ftp – Retrieve files with the File Transfer Protocol – example: “ftp ftp.kernel.org”

rlogin – Similar to telnet, but if you have a “.rhosts” file with allowed machines, you can log in without a password

rsh – Also using “.rhosts”, lets you run one command on another machine without logging in

rcp – Another that uses “.rhosts” and lets you copy files from another machine


alias – Aliases can be used to make a shortcut for a common command – example: “alias dir ‘ls -l'” or “alias dir=’ls -l'”, depending on shell

at – Lets you have a program run “at” a certain time

crontab – Schedule regular programs to run at certain times (some let all users have their own crontab file)

cal – Print a calendar for a given month – example: “cal 8 1976” or just “cal” for this month

date – Print current time and date

df – Find out how much free disk space is available – example: “df -k .” for current directory in kilobytes

du – Find out disk usage of a file or directory – example: “du -ks ~” for size of your entire home directory

echo – Repeats or echoes the argument – example: “echo hello” prints “hello”

tar – Tape ARchive – allows you to pack many files together – example: “tar -xvf file.tar” to extract

gzip, gunzip – Compress or uncompress *.gz files – example: “gzip file.tar”

passwd – Change your password on a system

spell – Spellcheck a text file against system dictionary – example: “spell paper.txt”

sort – Sort contents of a file

time – Get runtime of a program – example: “time ls -l”

uname – Get info on a machine – example: “uname -a”

uptime – Get how long a machine has been up

which, whence, where – File out which program you’ll be running, or where all occurences of a program is in your path – example: “which ls”

vi, pico, emacs, jed, joe – Text editors

pine, elm, mutt, mailx, mail – Email programs


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