As a developer, there are certain UNIX commands you find yourself typing repeatedly. Whether it’s to debug a production issue or just modifying some files, these commands have helped me do my job time and time again. Here’s my top 8:

1. grep – Prints the lines that match the pattern provided in the files specified
   • Usage: grep <options> <pattern> <files>
   • Example: grep -n Exception production.log
     • Prints all the line (showing line numbers) in the file production.log that contain the string ‘Exception’
2. tail – Only interested in a the last couple of lines in a file? tail allows you to quickly view the end of the file
   • Usage: tail <options> <file>
   • Example: tail -fn100 production.log
     • Shows the last 100 lines of the log and waits to display any new text appended to the file
3. ssh – Log into remote servers
   • Usage: ssh -p<port> <username>@<hostname>
   • Example: ssh -p1234 theo@production
     • Logs into the server named production on port 1234
4. scp – Copies files to/from remote servers
   • Usage: scp -P<port> <source> <target>
   • Example: scp -P1234 /home/theo/myfile.txt production@/home/jsmith
     • Copies myfile.txt from /home/theo to the server named production under /home/jsmith
5. rm – Deletes stuff!
   • Usage: rm <options> <file>
   • Example: rm -rf mydir
     • Removes the entire directory and files with no prompt for confirmation (Use with caution!)
6. ps – Shows process status
   • Usage: ps <options>
   • Example: ps aux
     • Displays the process status of processes for all users including those that are controlled by a terminal (system processes) sorted by CPU usage
7. top – Similar to ps but it periodically updates the information such as CPU and memory usage
   • Usage: top
   • Example: top (duh!)
8. kill – terminates a process
   • Usage: kill <option> <pid>
   • Example: kill -9 12345
     • Terminates the process with id of 12345 using a non-catchable, non-ignorable signal (that just means you REALLY mean to kill it)

I use lots of these commands in combination. For example, if tomcat seems to hang and won’t properly shut down I would do the following:

  >> ps aux | grep tomcat

I would then take the pid of tomcat and run:

  >> kill -9 <tomcat-pid>

Now you may be wondering why the “Top 8”, why not “Top 10”. Well, because 8 is the new 10 and those are all UNIX commands I know :).

What are some of the commands that you use to get through the day?