bash
SHORTCUTS and HISTORY
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+H -deletes one character under cursor (same as DELETE)
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 completions 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
ALT+B -moves backward one word
ALT+D -deletes next word
ALT+F -moves forward one word
ALT+H -deletes one character backward
ALT+T -transposes two words
ALT+. -pastes last word from the last command. Pressing it repeatedly traverses through command history.
ALT+U -capitalizes every character from the current cursor position to the end of the word
ALT+L -uncapitalizes every character from the current cursor position to the end of the word
ALT+C -capitalizes the letter under the cursor. The cursor then moves to the end of the word.
ALT+R -reverts any changes to a command you’ve pulled from your history if you’ve edited it.
BACKSPACE -deletes one character backward DELETE -deletes one character under cursor
history -shows command line history !! -repeats the last command !n -refers to command line 'n' !string -refers to command starting with 'string'
exit -logs out of current session
BASH BASICS
env -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 previously opened shell)
whereis bash -locates the binary, source and manual-page for a command
which bash -finds out which program is executed as 'bash' (default: /bin/bash, can change across environments)
clear -clears content on window (hide displayed lines)
FILE COMMANDS
ls -lists your files in current directory, ls dir to print files in a specific directory
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 in 'long format', including hidden files (name beginning with '.')
ln -s filename link -creates symbolic link to file
touch filename -creates or updates (edit) your file
cat filename -prints file raw content (will not be interpreted)
any_command filename -'' is used to perform redirections, it will set any_command's stdout to file instead of "real stdout" (generally /dev/stdout)
more filename -shows the first part of a file (move with space and type q to quit)
head filename -outputs the first lines of file (default: 10 lines)
tail filename -outputs the last lines of file (useful with -f option) (default: 10 lines)
vim filename -opens a file in VIM (VI iMproved) text editor, will create it if it does not exist
mv filename1 dest -moves a file to destination, behavior will change based on 'dest' type (dir: file is placed into dir; file: file will replace dest (tip: useful for renaming))
cp filename1 dest -copies a file
rm filename -removes a file
find . -name name type -searches for a file or a directory in the current directory and all its sub-directories by its name
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. Use -lwc (lines, word, character) to ouput only 1 of those informations
sort filename -sorts the contents of a text file line by line in alphabetical order, use -n for numeric sort and -r for reversing order.
sort -t -k filename -sorts the contents on specific sort key field starting from 1, using the field separator t.
chmod -options filename -lets you change the read, write, and execute permissions on your files (more infos: SUID, GUID)
gzip filename -compresses files using gzip algorithm
gunzip filename -uncompresses files compressed by gzip
gzcat filename -lets you look at gzipped file without actually having to gunzip it
lpr filename -prints the file
lpq -checks out the printer queue
lprm jobnumber -removes something from the printer queue
genscript -converts plain text files into postscript for printing and gives you some options for formatting
dvips filename -prints .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
head -n file_name | tail +n -Print nth line from file.
head -y lines.txt | tail +x -want to display all the lines from x to y. This includes the xth and yth lines.
DIRECTORY COMMANDS
mkdir dirname -makes a new directory rmdir dirname -remove an empty directory rmdir -rf dirname -remove a non-empty directory mv dir1 dir2 -rename a directory from dir1 to dir2 cd -changes to home cd .. -changes to the parent directory cd dirname -changes directory cp -r dir1 dir2 -copy dir1 into dir2 including sub-directories pwd -tells you where you currently are cd ~ -changes to home.
SSH, SYSTEM INFO & NETWORK COMMANDS
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 the processes with the ID you gave
killall processname -kill all processes with the name
top -displays your currently active processes
lsof -lists open files
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
VARIABLES
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
read varname -reads a string from the input and assigns it to a variable
let varname = equation -performs mathematical calculation using operators like +, -, *, /, %
export VARNAME=value -defines an environment variable (will be available in subprocesses)
array[0]=valA -how to define an array
array[1]=valB
array[2]=valC
array=([2]=valC [0]=valA [1]=valB) -another way
array=(valA valB valC) -and another
${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 treated as arrays
declare -f -uses function names only
declare -F -displays function names without definitions
declare -i -the variables are treated 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 occurrences of the given patterns
+(patternlist) -matches one or more occurrences of the given patterns
?(patternlist) -matches zero or one occurrence 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.
function functname() {
shell commands
}
unset -f functname -deletes a function definition
declare -f -displays all defined functions in your login session
FLOW CONTROLS
statement1 && statement2 -and operator
statement1 || statement2 -or operator
-a -and operator inside a test conditional expression
-o -or operator inside a test conditional expression
STRINGS
str1 == str2 -str1 matches str2
str1 != str2 -str1 does not match str2
str1 str2 -str1 is less than str2 (alphabetically)
str1 str2 -str1 is greater than str2 (alphabetically)
str1 \ str2 -str1 is sorted after str2
str1 \ str2 -str1 is sorted before str2
-n str1 -str1 is not null (has length greater than 0)
-z str1 -str1 is null (has length 0)
FILES
-a file -file exists or its compilation is successful
-d file -file exists and is a directory
-e file -file exists; same -a
-f file -file exists and is a regular file (i.e., not a directory or other special type of file)
-r file -you have read permission
-s file -file exists and is not empty
-w file -your have write permission
-x file -you have execute permission on file, or directory search permission if it is a directory
-N file -file was modified since it was last read
-O file -you own file
-G file -file's group ID matches yours (or one of yours, if you are in multiple groups)
file1 -nt file2 -file1 is newer than file2
file1 -ot file2 -file1 is older than file2
NUMBERS
-lt -less than
-le -less than or equal
-eq -equal
-ge -greater than or equal
-gt -greater than
-ne -not equal
if condition
then
statements
[elif condition
then statements...]
[else
statements]
fi
for x in {1..10}
do
statements
done
for name [in list]
do
statements that can use $name
done
for (( initialisation ; ending condition ; update ))
do
statements...
done
case expression in
pattern1 )
statements ;;
pattern2 )
statements ;;
esac
select name [in list]
do
statements that can use $name
done
while condition; do
statements
done
until condition; do
statements
done
COMMAND-LINE PROCESSING CYCLE
-The default order for command lookup is functions, followed by built-ins, with scripts and executables last.
-There are three built-ins that you can use to override this order: command, builtin and enable.
command -removes alias and function lookup. Only built-ins and commands found in the search path are executed
builtin -looks up only built-in commands, ignoring functions and commands found in PATH
enable -enables and disables shell built-ins
eval -takes arguments and run them through the command-line processing steps all over again
INPUT/OUTPUT REDIRECTORS
cmd1|cmd2 -pipe; takes standard output of cmd1 as standard input to cmd2
file -takes standard input from file
file -directs standard output to file
file -directs standard output to file; append to file if it already exists
|file -forces standard output to file even if noclobber is set
n|file -forces output to file from file descriptor n even if noclobber is set
file -uses file as both standard input and standard output
nfile -uses file as both input and output for file descriptor n
nfile -directs file descriptor n to file
nfile -takes file descriptor n from file
nfile -directs file description n to file; append to file if it already exists
n& -duplicates standard output to file descriptor n
n& -duplicates standard input from file descriptor n
n&m -file descriptor n is made to be a copy of the output file descriptor
n&m -file descriptor n is made to be a copy of the input file descriptor
&file -directs standard output and standard error to file
&- -closes the standard input
&- -closes the standard output
n&- -closes the ouput from file descriptor n
n&- -closes the input from file descripor n
PROCESS HANDLING
-To suspend a job, type CTRL+Z while it is running. You can also suspend a job with CTRL+Y.
-This is slightly different from CTRL+Z in that the process is only stopped when it attempts to read input from terminal.
-Of course, to interrupt a job, type CTRL+C.
myCommand & -runs job in the background and prompts back the shell
jobs -lists all jobs (use with -l to see associated PID)
fg -brings a background job into the foreground
fg %+ -brings most recently invoked background job
fg %- -brings second most recently invoked background job
fg %N -brings job number N
fg %string -brings job whose command begins with string
fg %?string -brings job whose command contains string
kill -l -returns a list of all signals on the system, by name and number
kill PID -terminates process with specified PID
kill -s SIGKILL 4500 -sends a signal to force or terminate the process
kill -15 913 -Ending PID 913 process with signal 15 (TERM)
kill %1 -Where %1 is the number of job as read from 'jobs' command.
ps -prints a line of information about the current running login shell and any processes running under it
ps -a -selects all processes with a tty except session leaders
trap cmd sig1 sig2 -executes a command when a signal is received by the script
trap "" sig1 sig2 -ignores that signals
trap - sig1 sig2 -resets the action taken when the signal is received to the default
disown PID|JID -removes the process from the list of jobs
wait -waits until all background jobs have finished
TIPS & TRICKS
-set an alias
cd; nano .bash_profile
alias gentlenode='ssh admin@gentlenode.com -p 3404' -add your alias in .bash_profile
-to quickly go to a specific directory
cd; nano .bashrc
shopt -s cdable_vars
export websites="/Users/mac/Documents/websites"
source .bashrc
cd $websites
DEBUGGING SHELL PROGRAMS
bash -n scriptname -don't run commands; check for syntax errors only
set -o noexec -alternative (set option in script)
bash -v scriptname -echo commands before running them
set -o verbose -alternative (set option in script)
bash -x scriptname -echo commands after command-line processing
set -o xtrace -alternative (set option in script)
trap 'echo $varname' EXIT -useful when you want to print out the values of variables at the point that your script exits
function errtrap {
es=$?
echo "ERROR line $1: Command exited with status $es."
}
trap 'errtrap $LINENO' ERR -is run whenever a command in the surrounding script or function exits with non-zero status
function dbgtrap {
echo "badvar is $badvar"
}
trap dbgtrap DEBUG -causes the trap code to be executed before every statement in a function or script
-...section of code in which the problem occurs...
trap - DEBUG -turn off the DEBUG trap
function returntrap {
echo "A return occurred"
}
trap returntrap RETURN -is executed each time a shell function or a script executed with the . or source commands finishes executing
COLORS AND BACKGROUNDS
-Reset
Color_Off='\033[0m' -Text Reset
-Regular Colors
Black='\033[0;30m' -Black
Red='\033[0;31m' -Red
Green='\033[0;32m' -Green
Yellow='\033[0;33m' -Yellow
Blue='\033[0;34m' -Blue
Purple='\033[0;35m' -Purple
Cyan='\033[0;36m' -Cyan
White='\033[0;97m' -White
-Additional colors
LGrey='\033[0;37m' -Ligth Gray
DGrey='\033[0;90m' -Dark Gray
LRed='\033[0;91m' -Ligth Red
LGreen='\033[0;92m' -Ligth Green
LYellow='\033[0;93m'-Ligth Yellow
LBlue='\033[0;94m' -Ligth Blue
LPurple='\033[0;95m'-Light Purple
LCyan='\033[0;96m' -Ligth Cyan
-Bold
BBlack='\033[1;30m' -Black
BRed='\033[1;31m' -Red
BGreen='\033[1;32m' -Green
BYellow='\033[1;33m'-Yellow
BBlue='\033[1;34m' -Blue
BPurple='\033[1;35m'-Purple
BCyan='\033[1;36m' -Cyan
BWhite='\033[1;37m' -White
-Underline
UBlack='\033[4;30m' -Black
URed='\033[4;31m' -Red
UGreen='\033[4;32m' -Green
UYellow='\033[4;33m'-Yellow
UBlue='\033[4;34m' -Blue
UPurple='\033[4;35m'-Purple
UCyan='\033[4;36m' -Cyan
UWhite='\033[4;37m' -White
-Background
On_Black='\033[40m' -Black
On_Red='\033[41m' -Red
On_Green='\033[42m' -Green
On_Yellow='\033[43m'-Yellow
On_Blue='\033[44m' -Blue
On_Purple='\033[45m'-Purple
On_Cyan='\033[46m' -Cyan
On_White='\033[47m' -White
-Example of usage
echo -e "${Green}This is GREEN text${Color_Off} and normal text"
echo -e "${Red}${On_White}This is Red test on White background${Color_Off}"