Linux Commands for Real Life with Examples

Practical Linux Commands for Real Life With Example This article is part of the Linux Commands for Real Life series, Part - 1 https://goo.gl/6oPfMG Part - 2 https://goo.gl/WxxGLl Written Tutorial Part 1: https://goo.gl/XcayZn Written Tutorial Part 2: https://goo.gl/fbchIw Using cut command with cat Sometimes when i am writing a script and i want to find out the name of the server, network type...etc i use the below command. I use cat to screen all the file content, i use grep after to find specific line then i cut only specific part. Command: cat /etc/sysconfig/network-scripts/ifcfg-eth0 | grep -i TYPE | cut -d "=" -f 2 Output: "Ethernet" Explanation: grep -i type - Find line which has type cut -d "=" -f 2 - use "=" as a delimeter and -f 2 means show  the second column. Another example: if you have a file which contains type=3=4=5=6 Then you use cat that file and -d "=" and -f 3 then the output will be '4' as 4 is the third column. Change text color using tput You can change text output color/bold/italic/backgroun color using tput. Example: echo "$(tput smul)$(tput setaf 1)Text$(tput sgr0)": Output: Explanation $(tput smul) - Underline $(tput setaf 1) - Text color is red $(tput sgr0) - this part you should put it at the end to get the text back to normal, if you don't put it all the tyle will be applied to all the next written text. Sort processes by CPU usage Command ps -e --sort -pcpu -o comm,pcpu,user,pid | head -11 Output COMMAND %CPU USER PID systemd 50.0 root 1 kthreadd 44.0 root 2 ksoftirqd/0 38.0 root 3 kworker/u30:10 0.0 root 6 migration/0 8.0 root 7 rcu_bh 0.0 root 8 rcu_sched 0.0 root 9 watchdog/0 0.0 root 10 khelper 0.0 root 12 kdevtmpfs 0.0 root 13 Explanation --sort -pcpu , Sort by CPU Usage -o comm,pcpu,user,pid , show output columns of cpu, user,process id. | head 11 , show top 11 Rename multiple files with specific name with number sequence Below example will rename multiple files which starting with x to data01.csv , data02.csv ...etc ls x[a-z]* | while read file;do let c++;mv $file data$(printf "%02d" $c)".csv";done Explanation: ls x[a-z]* - List all the files which start with 'x' letter while read file;do let c++ - Loop while listing all the files and do the following mv $file data$(printf "%02d" $c)".csv";done - Move all the files with naming them 'data' and have 0 then number of the loop of $c and place extension .csv Check each installed packaged information and sort by date Not all the installed packages' information can be retreived using yum, if packages where installed using rpm you can query and find installation date using below command: Example: rpm -qa --qf  '%{INSTALLTIME} (%{INSTALLTIME:date}): %{NAME}-%{VERSION}-%{RELEASE}.%{ARCH}\n' | sort -n | tail -n5 Output sample: 1496198202(Tue 30 May 2017 10:36:42 PM EDT):mysql-community-common-5.7.18-1.el7 1496198203(Tue 30 May 2017 10:36:43 PM EDT):mysql-community-libs-5.7.18-1.el7 1496198207(Tue 30 May 2017 10:36:47 PM EDT):mysql-community-client-5.7.18-1.el7 1496198234(Tue 30 May 2017 10:37:14 PM EDT):mysql-community-server-5.7.18-1.el7 1496198235(Tue 30 May 2017 10:37:15 PM EDT):mysql-community-libs-compat-5.7.18-1.el7 Explanation: rpm -qa --qf '%{INSTALLTIME}(%{INSTALLTIME:date}):%{NAME}-%{version}-%{RELEASE}\n' | sort -n | tail -n 5 rpm -qa - List and query all installed packages. --qf '%{INSTALLTIME}' - This will show file information of Install Time and all the rest of parameters have different info like date, name, version..etc \n' - To have each package in a new line sort -n - Sort the list tail -n5 - List only the latest 5 installed packages Find Apache uptime or when was restarted Method #1 apachectl status | grep -i active Method #2 locate error_log cat /var/log/httpd/error_log | grep -i resum List files by last accessed ones ls -latu This command will differ than ls -lat that it will show last accessed even if it was not modified. Which processes using certain file Example: fuser /var/log/httpd/error_log Output example: /var/log/httpd/error_log: 27431 27432 27433 27434 27435 27436 Investigate certain pid ps aux | grep -i 27431 Output will show that httpd is running, now we can know that httpd is using that file.