Shell usage and skills

Check whether the remote port is open to bash:

echo >/dev/tcp/8.8.8.8/53 && echo "open"

Transfer the process to the background:

Ctrl + z

Switch the process to the foreground:

fg

Generate a random hexadecimal number, where n is the number of characters:

openssl rand -hex n

Execute the command in a file in the current shell:

source /home/user/file.name

Extract the first five characters:

${variable:0:5}

SSH debug mode:

ssh -vvv user@ip_address

SSH with pem key:

ssh user@ip_address -i key.pem

Use wget to capture the complete website directory structure and store it in the local directory:

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

Create multiple directories at a time:

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

List the process trees that contain sub-processes:

ps axwef

Create a war file:

jar -cvf name.war file

Test hard disk write speed:

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

Test hard disk read speed:

hdparm -Tt /dev/sda

Obtain the md5 hash of text:

echo -n "text" | md5sum

Check xml format:

xmllint --noout file.xml

Extract tar.gz to the new directory:

tar zxvf package.tar.gz -C new_dir

Use curl to obtain HTTP header information:

curl -I http://www.example.com

Modify the timestamp of a file or directory (YYMMDDhhmm ):

touch -t 0712250000 file

Run the wget command to download ftp:

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

Generate a random password (in this example, it is 16 characters long ):

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

Quickly back up a file:

cp some_file_name{,.bkp}

Access the Windows shared directory:

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

Execute the commands in the History (here is the 100th line ):

!100

Decompress:

unzip package_name.zip -d dir_name

Enter multiple lines of text (CTRL + d to exit ):

cat > test.txt

Create an empty file or clear an existing file:

> test.txt

Synchronization time with Ubuntu NTP server:

ntpdate ntp.ubuntu.com

Use netstat to display all tcp4 listening ports:

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

Qcow2 image file conversion:

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

Run the file repeatedly and display its output (the default value is 2 seconds ):

watch ps -ef

List of all users:

getent passwd

Mount root in read/write mode:

mount -o remount,rw /

Mount a directory (this is the case where the link cannot be used ):

mount --bind /source /destination

Dynamically update the DNS server:

nsupdate < <EOFupdate add $HOST 86400 A $IPsendEOF

Recursive grep all directories:

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

List the top 10 largest files:

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

Show remaining memory (MB ):

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

Open Vim and jump to the end of the file:

vim + some_file_name

Git clone the specified Branch (master ):

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

Switch Git to another branch (develop ):

git checkout develop

Myfeature ):

git branch -d myfeature

Git deletes a remote Branch

git push origin :branchName

Git pushes the new branch to the remote server:

git push -u origin mynewfeature

Print the last cat command in the history:

!cat:p

The last cat command in the running history:

!cat

Find all empty sub-directories under/home/user:

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

Line 50-60 in the test.txt file:

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

Run the last command (if the last command is mkdir/root/test, run: sudo mkdir/root/test ):

sudo !!

Create a temporary RAM File System-ramdisk (first create the/tmpram directory ):

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

Grep whole words:

grep -w "name" test.txt

Append the text to a file when you need to escalate permissions:

echo "some text" | sudo tee -a /path/file

List all kill signal parameters:

kill -l

Do not record the last session in the bash history:

kill -9 $$

Scan the network to find open ports:

nmap -p 8081 172.20.0.0/16

Set git email:

git config --global user.email "me@example.com"

To sync with master if you have unpublished commits:

git pull --rebase origin master

Move all files whose names contain "txt" to the/home/user directory:

find -iname "*txt*" -exec mv -v {} /home/user \;

Display files in parallel by row:

paste test.txt test1.txt

Shell progress bar:

pv data.log

Use netcat to send data to Graphite server:

echo "hosts.sampleHost 10 `date +%s`" | nc 192.168.200.2 3000

Convert tabs to a space:

expand test.txt > test1.txt

Skip bash history:

< space >cmd

Go to the previous working directory:

cd -

Split the tar.gz file (100 MB each) and merge it back:

split –b 100m /path/to/large/archive /path/to/output/filescat files* > archive

Use curl to obtain the HTTP status code:

curl -sL -w "%{http_code}\\n" www.example.com -o /dev/null

Set the root password to enhance the secure installation of MySQL:

/usr/bin/mysql_secure_installation

When Ctrl + c is not easy to use:

Ctrl + \

Get the file owner:

stat -c %U file.txt

Block device list:

lsblk -f

Find the file with spaces at the end of the file name:

find . -type f -exec egrep -l " +$" {} \;

Find the file with tab indentions in the file name.

find . -type f -exec egrep -l $'\t' {} \;

Print the horizontal line with "=:

printf '%100s\n' | tr ' ' =

[Original article: Linux shell tips and tricks]