Recently I had some folks watching my shared screen and they were constantly saying “oh, that was cool, I didn’t know you could do that in the shell”.

If you’ve been working on the shell (here I’m talking about bash) day in and day out for years, you might know some of these.  But a lot of people are occasional shell users, or adjacent shell users.  They’re not grizzled Unix vets but rather developers, DBAs, or other people who use the shell as a user but have never really read a book about it.

Here’s some cool tricks you can use to make your interactive shell experience more pleasant.  I’m not talking about shell programming (writing shell scripts) but rather working at the prompt.

Go Into the Directory You Just Made

mkdir /some/long/path/that/is/a/pain/to/type
cd $_

This is faster than typing “cd /some/long/path…”.  The $_ variable picks up the last item in your previous command.

Jumping Around the Line

control-A will jump your cursor to the start of the line

control-E will jump your cursor to the end of the line

So if you start to type…

kdir /some/long/path/that/is/a/pain/to/type

And then realize you forgot the “m” in “mkdir”, you can hit control-A, add it, and then either hit ENTER to submit the command or control-E to jump back to the end of the line and continue typing.  If you’d hit ENTER already and got an error, then the up arrow would move back in history.  Speaking of which…

History

The

history

command will show you your history.  Let’s say it looks like this:

551  ssh user@server
552  vi /tmp/file
553  grep Prod /some/other/file

If you want to rerun that vi command, you can type

!552

You can also do

!vi

Be careful with this last form!  Rerunning with the command number always gives you the exact command, but something like

!r

will rerun the last command that starts with r.  Might be “rm /some/file”.  Might be “rm -rf *”.

You type control-R to search through your history.

When You’ve Typed a Long Command But Don’t Want to Run it

So you’ve typed something like this:

cp /some/long/path/to/files/*.csv /some/other/long/directory/that/is/a/pain/to/type

And just as you get to the end you realize that you haven’t created /some/other/long/directory/that/is/a/pain/to/type yet.  Rather than cancel the command and go create the directory and retype the command, you can do this: hit  control-A, type # to insert the comment character at the start of the line, and then hit return.

Now this long command is in your history.  You can go create the directory, and then scroll back (up arrow) to this command, hit control-A, remove the #, and hit ENTER.

Conditional Execution

You can execute multiple commands on one line by separating them with semi-colons:

command1 ; command2

But what if you don’t want command2 to run unless command1 succeeds?  For example:

mkdir /tmp/blah ; cd /tmp/blah ; cp /somewhere/*.csv .

If the mkdir and cd fails, you don’t want the cp to run.  Instead of semi-colons, use the logical operator for “and”:

mkdir /tmp/blah && cd /tmp/blah && cp /somewhere/*.csv .

This will stop execution once any command fails.

Watch a Command

Let’s say you have a long copy, rsync, etc. process going.  You want to watch how it’s going.  What you want is to run du -sh (“disk usage, summary, human-readable output”) every 60 seconds.  In ages past you’d do something like:

while [ 1 ] ; do echo ; date ; du -sh /dest/dir ; sleep 60; done

That still works, but this is simpler:

watch -n 60 /dest/dir

What’s your favorite Linux shell trick?  Drop it in the comments below!

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raindog308

Dread Lord of LowEnd Content at LowEndBox

I'm raindog308, techno polymath and long-time LowEndTalk community Administrator. My technical interests include all things Unix, perl, python, golang, shell scripting, vintage operating systems such as MVS, and relational database systems such as Oracle, PostgreSQL, and MySQL.

I also enjoy using LEBs! I have an empire of little guys for VPNs, larger guys for apps, and big guys for databases and storage. When I'm not in front a screen I'm into German Shepherd dogs, quality knives, target shooting, theology, tabletop roleplaying games, and forest hiking.

I enjoy writing technical articles here on LowEndBox to help people get more out of their systems. You can find me on LowEndTalk @raindog308

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