Advanced Linux Commands for Developers
I have curated some of the most useful commands that Software Developers / DevOps Engineers often use.
I’m not covering the basic ones like — mkdir, rm, cat, cd, etc. Some medium to advanced commands…
grep
cat sample.txt | grep -i “TIM”-i for case ignore
Or
grep -i “TIM” sample.txt
In case you don’t know the file name, but just a text from a folder full of files, you might want to use this.
grep -irw -e "text to find"Note: -n with grep will show the line numbers
find
find . -type f -name “*.csv” #type can be f — folder, d — directory# exclude name search during findfind . -type f -not -name "*.csv"
awk
awk can be used to split a line in a file and process (with delimiter)
sed
Is a stream editor, can be used to find / replace / insert / delete in a file.
netstat
netstat -tnpl | grep -i LISTENWill help to find the list of Listeners
lsof
lsof does a similar to netstat, but we can give specific port and check
lsof -t -i:<port_number> (list of open files)lsof -i tcp (list of files opened by network tcp)lsof -u <username> (list of files opened by user)lsof -I TCP:<port number>
cut
helps to split a text (line / string level manipulation)
cat <file> | cut -d (Delimiter) ‘<single_char>’ -f <nth element to cutting>curl
used to make API calls to system (REST / SOAP)
curl -ik “http://localhost:5000/health”
-k : used to bypass insecure network
kill (with SIGNALS)
The basics of kill is to simply kill a program running (given a pid).
Kill can also be used to send SIGNALS (OS Signals). Ex: HUP Signal
kill -s HUP <pid>
The above command becomes handy to reload a service without restarting. Can be used to reload, when a configuration has been changed / updated.
telnet
to check if a remote listener is active on a specific port
telnet <host_name> <port_no>
nslookup
Helpful in DNS resolution — especially to check if load balancers are working properly
nslookup <dns>
Array Usage
car=(‘BMW’ ‘TOYOTA’ ‘HONDA’ ‘ROVER’)echo “${car[@]}” # print all values with spaceecho “${!car[@]}” # print only the indexesecho “${#car[@]}” # print the total number availableecho “${car[1]}” # print value based on index
Looping through file (one line at a time)
for file in `cat sample.txt` do echo $file done 
Machine Stats
top — will give the running stats (machine usage)
vmstat — will give the free, swap spaces and other details of CPU & Memory
Piping
Piping helps the output of first command to be used by next one — without using any variables (like a stream)
Commonly piped commands — cat, grep, find, sort, awktar Commands
# creation of tar file
tar -cvf <tar_file_name> <list of files to be compressed># unzip tar files
tar -xvf <tar_file_name>
sort
cat sample.txt | awk ‘{print $1}’ | sort
reverse-search
CTRL + R — and start typing few chars, based on the history the previous commands will be displayed.
Use CTRL + R to move back and CTRL + F to move next
run a script in background
nohup /tmp/run.sh &Firewall Commands
iptables -Fiptables -t nat -Fiptables -t nat -Xiptables -t mangle -Fiptables -t mangle -Xiptables -P INPUT ACCEPTiptables -P OUTPUT ACCEPTiptables -P FORWARD ACCEPT
Saving IP Table Rules
iptables-save > /tmp/firewall.rulesip6tables-save > /tmp/firewall6.rules
Command to kill a process (grep and kill) — single line command
ps -elf | grep -i <process> | awk ‘{print $2}’ | xargs kill -9
# if the process is running on a PORTlsof -i -P -n | grep LISTEN | grep -i 8080 | awk '{print $2}' | xargs kill -9
I’ll try to keep this list updated whenever i find something interesting
-cheers
