I often find myself mentoring young colleagues in the ways of Linux.  If they’re coming from a Windows background or just haven’t had a lot of time in IT, there’s a lot to learn to really be proficient in Unix/Linux.  You need to figure out an editor, how to move around the filesystem, where things in the filesystem, basic tools (cp, mv, ps, grep, etc.), how permissions work, pipelining commands, etc.

Once people are comfortable, they often enter a mind-expansion phases where they realize all the power they have at their disposal.  As they enter their journeyman phase of using Linux, they’re getting into shell scripting, building little tools, learning regular expresisons, and maybe starting to learn languages like python or awk/perl.  What was once someone who googled for answers blossoms into someone who reads the man pages.

At the advanced journeyman stage, I often share little tips and tricks that make life easier.  Here are a few of my favorites.

Use Braces for Bulk Directory Creation

Did you know you can do this?

mkdir /some/path/{bin,doc,src,test}

That will create:

/some/path/bin
/some/path/doc
/some/path/src
/some/path/test

Get Rid of Backslashitis

If you write regular expressions and get tired of writing things like this:

sed 's/\/that\/is\/long/\/new\/path/'

then I have very good news for you.  Read the post.

The timeout Command

If you’re writing a script that does something like “connect to these 10 hosts and do X” and one of the hosts is down, the script can hang.  But you can use the timeout command.  Something like

timeout 10s /do/some/command

After 10 seconds, it will kill the command and error out.

Turn Any Command into a Stopwatch with time

Speaking of time, you can run a command like this:

time /some/command

and record how long it took:

# time ./purge_logs.sh 

real 0m2.608s
user 0m2.490s
sys 0m0.794s

Use grep -R --include to Narrow Recursive Searches

If you do a grep -R, sometimes you find it chewing through tons of files you’re not interested in.  Want to only look at the .conf files in /etc?  Try this:

grep -R –include=”*.conf” “listen” /etc

Record Your Session

Type

script session.log

and you’ll find every command you typed in session.log.

Setup Detachable and Reattachable Terminal Sessions

Did you know you can start a session, turn off the session, and later come back to it?  Yup – check out tmux.

The Human Flag

Both du (disk used) and df (disk free) support a -h flag which translates the output into human-readable terms.  Instead of blocks, get MBs, GBs, or TBs.

# df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            3.9G     0  3.9G   0% /dev
tmpfs           795M  524K  794M   1% /run
/dev/sda1        19G  9.4G  7.9G  55% /
tmpfs           3.9G  224K  3.9G   1% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           795M     0  795M   0% /run/user/0

Duplicate a Directory Perfectly with tar

# cd /SRC && tar cf - . | (cd /DST && tar xpf - )

Grab Random Lines From a File

Want some random log entries?  Use shuf:

shuf -n 20 bigfile.log

raindog308

Raindog308 is a longtime LowEndTalk community administrator, technical writer, and self-described techno polymath. With deep roots in the *nix world, he has a passion for systems both modern and vintage, ranging from Unix, Perl, Python, and Golang to shell scripting and mainframe-era operating systems like MVS. He’s equally comfortable with relational database systems, having spent years working with Oracle, PostgreSQL, and MySQL.

As an avid user of LowEndBox providers, Raindog runs an empire of LEBs, from tiny boxes for VPNs, to mid-sized instances for application hosting, and heavyweight servers for data storage and complex databases. He brings both technical rigor and real-world experience to every piece he writes.

Beyond the command line, Raindog is a lover of German Shepherds, high-quality knives, target shooting, theology, tabletop RPGs, and hiking in deep, quiet forests.

His goal with every article is to help users, from beginners to seasoned sysadmins, get more value, performance, and enjoyment out of their infrastructure.

You can find him daily in the forums at LowEndTalk under the handle @raindog308.