Basics
export # displays all environment variables
echo $SHELL # displays the shell you're using
echo $BASH_VERSION # displays bash version
bash # if you want to use bash (type exit to go back to your normal shell)
whereis bash # finds out where bash is on your system
clear # clears content on window (hide displayed lines)
File Commands
ls # lists your files
ls -l # lists your files in 'long format', which contains the exact size of the file, who owns the file and who has the right to look at it, and when it was last modified
ls -a # lists all files, including hidden files
ln -s <filename> <link> # creates symbolic link to file
touch <filename> # creates or updates your file
cat > <filename> # places standard input into file
more <filename> # shows the first part of a file (move with space and type q to quit)
head <filename> # outputs the first 10 lines of file
tail <filename> # outputs the last 10 lines of file (useful with -f option)
emacs <filename> # lets you create and edit a file
mv <filename1> <filename2> # moves a file
cp <filename1> <filename2> # copies a file
rm <filename> # removes a file
diff <filename1> <filename2> # compares files, and shows where they differ
wc <filename> # tells you how many lines, words and characters there are in a file
chmod -options <filename> # lets you change the read, write, and execute permissions on your files
gzip <filename> # compresses files
gunzip <filename> # uncompresses files compressed by gzip
gzcat <filename> # lets you look at gzipped file without actually having to gunzip it
lpr <filename> # print the file
lpq # check out the printer queue
lprm <jobnumber> # remove something from the printer queue
genscript # converts plain text files into postscript for printing and gives you some options for formatting
dvips <filename> # print .dvi files (i.e. files produced by LaTeX)
grep <pattern> <filenames> # looks for the string in the files
grep -r <pattern> <dir> # search recursively for pattern in directory
Shortcuts
CTRL+A # move to beginning of line
CTRL+B # moves backward one character
CTRL+C # halts the current command
CTRL+D # deletes one character backward or logs out of current session, similar to exit
CTRL+E # moves to end of line
CTRL+F # moves forward one character
CTRL+G # aborts the current editing command and ring the terminal bell
CTRL+J # same as RETURN
CTRL+K # deletes (kill) forward to end of line
CTRL+L # clears screen and redisplay the line
CTRL+M # same as RETURN
CTRL+N # next line in command history
CTRL+O # same as RETURN, then displays next line in history file
CTRL+P # previous line in command history
CTRL+R # searches backward
CTRL+S # searches forward
CTRL+T # transposes two characters
CTRL+U # kills backward from point to the beginning of line
CTRL+V # makes the next character typed verbatim
CTRL+W # kills the word behind the cursor
CTRL+X # lists the possible filename completefions of the current word
CTRL+Y # retrieves (yank) last item killed
CTRL+Z # stops the current command, resume with fg in the foreground or bg in the background
DELETE # deletes one character backward
!! # repeats the last command
exit # logs out of current session
Directory Commands
mkdir <dirname> # makes a new directory
cd # changes to home
cd <dirname> # changes directory
pwd # tells you where you currently are
SSH/System Info/Network
ssh user@host # connects to host as user
ssh -p <port> user@host # connects to host on specified port as user
ssh-copy-id user@host # adds your ssh key to host for user to enable a keyed or passwordless login
whoami # returns your username
passwd # lets you change your password
quota -v # shows what your disk quota is
date # shows the current date and time
cal # shows the month's calendar
uptime # shows current uptime
w # displays whois online
finger <user> # displays information about user
uname -a # shows kernel information
man <command> # shows the manual for specified command
df # shows disk usage
du <filename> # shows the disk usage of the files and directories in filename (du -s give only a total)
last <yourUsername> # lists your last logins
ps -u yourusername # lists your processes
kill <PID> # kills (ends) the processes with the ID you gave
killall <processname> # kill all processes with the name
top # displays your currently active processes
bg # lists stopped or background jobs ; resume a stopped job in the background
fg # brings the most recent job in the foreground
fg <job> # brings job to the foreground
ping <host> # pings host and outputs results
whois <domain> # gets whois information for domain
dig <domain> # gets DNS information for domain
dig -x <host> # reverses lookup host
wget <file> # downloads file
Variable
varname=value # defines a variable
varname=value command # defines a variable to be in the environment of a particular subprocess
echo $varname # checks a variable's value
echo $$ # prints process ID of the current shell
echo $! # prints process ID of the most recently invoked background job
echo $? # displays the exit status of the last command
export VARNAME=value # defines an environment variable (will be available in subprocesses)
array[0] = val # several ways to define an array
array[1] = val
array[2] = val
array=([2]=val [0]=val [1]=val)
array(val val val)
${array[i]} # displays array's value for this index. If no index is supplied, array element 0 is assumed
${#array[i]} # to find out the length of any element in the array
${#array[@]} # to find out how many values there are in the array
declare -a # the variables are treaded as arrays
declare -f # uses funtion names only
declare -F # displays function names without definitions
declare -i # the variables are treaded as integers
declare -r # makes the variables read-only
declare -x # marks the variables for export via the environment
${varname:-word} # if varname exists and isn't null, return its value; otherwise return word
${varname:=word} # if varname exists and isn't null, return its value; otherwise set it word and then return its value
${varname:?message} # if varname exists and isn't null, return its value; otherwise print varname, followed by message and abort the current command or script
${varname:+word} # if varname exists and isn't null, return word; otherwise return null
${varname:offset:length} # performs substring expansion. It returns the substring of $varname starting at offset and up to length characters
${variable#pattern} # if the pattern matches the beginning of the variable's value, delete the shortest part that matches and return the rest
${variable##pattern} # if the pattern matches the beginning of the variable's value, delete the longest part that matches and return the rest
${variable%pattern} # if the pattern matches the end of the variable's value, delete the shortest part that matches and return the rest
${variable%%pattern} # if the pattern matches the end of the variable's value, delete the longest part that matches and return the rest
${variable/pattern/string} # the longest match to pattern in variable is replaced by string. Only the first match is replaced
${variable//pattern/string} # the longest match to pattern in variable is replaced by string. All matches are replaced
${#varname} # returns the length of the value of the variable as a character string
*(patternlist) # matches zero or more occurences of the given patterns
+(patternlist) # matches one or more occurences of the given patterns
?(patternlist) # matches zero or one occurence of the given patterns
@(patternlist) # matches exactly one of the given patterns
!(patternlist) # matches anything except one of the given patterns
$(UNIX command) # command substitution: runs the command and returns standard output
Functions
# The function refers to passed arguments by position (as if they were positional parameters), that is, $1, $2, and so forth.
# $@ is equal to "$1" "$2"... "$N", where N is the number of positional parameters. $# holds the number of positional parameters.
functname() {
shell commands
}
unset -f functname # deletes a function definition
declare -f # displays all defined functions in your login session