Linux shell tips and tricks

I’m using Linux shell on daily basis, but I often forgot some useful command or shell tip. Yes, I can remember commands, but I can’t say that if I used it just once for specific task. Then I started to write Linux shell tips in text file on my Dropbox account and now I decided to share that. This list will be updated over time. Also keep in mind that for some tips you will need to install additional software on your Linux distribution.


UPDATE: June 15, 2013

Send process to background:


Ctrl + z


Move process to foreground:


fg


Generate random hex number where n is number of characters:


openssl rand -hex n


Execute commands from a file in the current shell:


source /home/user/file.name


Substring for first 5 characters:


${variable:0:5}


SSH debug mode:


ssh -vvv user@ip_address


SSH with pem key:


ssh user@ip_address -i key.pem


Get complete directory listing to local directory with wget:


wget -r --no-parent --reject "index.html*" http://hostname/ -P /home/user/dirs


Create multiple directories:


mkdir -p /home/user/{test,test1,test2}


List processes tree with child processes:


ps axwef


Create war file:


jar -cvf name.war file


Test disk write speed:


dd if=/dev/zero of=/tmp/output.img bs=8k count=256k; rm -rf /tmp/output.img


Test disk read speed:


hdparm -Tt /dev/sda


Get md5 hash from text:


echo -n "text" | md5sum


Check xml syntax:


xmllint --noout file.xml


Extract tar.gz in new directory:


tar zxvf package.tar.gz -C new_dir


Get web headers with curl:


curl -v -D - http://hostname -o /dev/null


Modify timestamp of some file or directory (YYMMDDhhmm):


touch -t 0712250000 file


Download from ftp using wget:


wget -m ftp://username:password@hostname


Generate random password (16 char long in this case):


LANG=c < /dev/urandom tr -dc _A-Z-a-z-0-9 | head -c${1:-16};echo;


Quickly create a backup of a file:


cp some_file_name{,.bkp}


Access Windows share:


smbclient -U "DOMAIN\user" //dc.domain.com/share/test/dir


Run command from history (here at line 100):


!100


Unzip to directory:


unzip package_name.zip -d dir_name


Multiline text (CTRL + d to exit):


cat > test.txt


Create empty file or empty existing one:


> test.txt


Update date from Ubuntu NTP server:


ntpdate ntp.ubuntu.com

netstat show all tcp4 listening ports:

netstat -lnt4 | awk '{print $4}' | cut -f2 -d: | grep -o '[0-9]*'


Convert image from qcow2 to raw:


qemu-img convert -f qcow2 -O raw precise-server-cloudimg-amd64-disk1.img \

precise-server-cloudimg-amd64-disk1.raw


Run command repeatedly, displaying it’s output (default every two seconds):


watch ps -ef


List all users:


getent passwd


Mount root in read/write mode:


mount -o remount,rw /


Mount a directory (for cases when symlinking will not work):


mount --bind /source /destination


Send dynamic update to DNS server:


nsupdate <<EOF

update add $HOST 86400 A $IP

send

EOF


Recursively grep all directories:


grep -r "some_text" /path/to/dir


List ten largest open files:


lsof / | awk '{ if($7 > 1048576) print $7/1048576 "MB "$9 }' | sort -n -u | tail


Show free RAM in MB:


free -m | grep cache | awk '/[0-9]/{ print $4" MB" }'


Open Vim and jump to end of file:


vim + some_file_name


Git clone specific branch (master):


git clone git@github.com:name/app.git -b master


Git switch to another branch (develop):


git checkout develop


Git delete branch (myfeature):


git branch -d myfeature


Git delete remote branch:


git push origin :branchName


Git push new branch to remote:


git push -u origin mynewfeature


Print out the last cat command from history:


!cat:p


Run your last cat command from history:


!cat


Find all empty subdirectories in /home/user:


find /home/user -maxdepth 1 -type d -empty


Get all from line 50 to 60 in test.txt:


< test.txt sed -n '50,60p'


Run last command (if it was: mkdir /root/test, below will run: sudo mkdir /root/test):


sudo !!


Create temporary RAM filesystem – ramdisk (first create /tmpram directory):


mount -t tmpfs tmpfs /tmpram -o size=512m


Grep whole words:


grep -w "name" test.txt


UPDATE: June 15, 2013

Source:http://www.techbar.me/linux-shell-tips/