Re-posted from Command Line Kung Fu blog here. Check out the link for how to save time with commonly used commands on other platforms.
Saving time? Who wants to save time? I thought the whole point of CLI tricks was to make things as painful and as drawn out as possible? Oh wait, that’s the job of some of the curlers in Vancouver.
When you start talking about an alias on a Mac, the first thing any Mac user is going to think of is a GUI pointer, otherwise known in Mac land as an Alias. These have existed long before the days of OS X and while not as powerful as say Unix Symbolic Links, they do have some nice features. For example, if you move a target file of an alias, the alias will still work as long as the target is on the same file system. Sadly though, they don’t work from the command line. Use good old ln for that.
But I get off topic. I’m disappointed in Hal; for all his talk about being quick on the draw and not letting the boss see you enjoying that wonderful concoction of roasted bean water and barley, he doesn’t take his shell fu to the next level.
Hal left us with:
$ function f { cd `dirname $_`; }
$ cp ~/.bashrc ~/stuff/testing/src/clkf/aliases/bashrc.example
$ f
$ pwd
/home/hal/stuff/testing/src/clkf/aliases
Great! But who’s to say we can’t use aliases?
$ alias lastdir='function f { cd `dirname $_`; }; f; echo Your working directory is now $PWD'
$ cp ~/.bashrc ~/stuff/testing/src/clkf/aliases/bashrc.example
$ lastdir
Your working directory is now /home/hal/stuff/testing/src/clkf/aliases
Now you might ask, what’s the point of wrapping a function into an alias, it’s extra unneeded text in an already beautiful simple command! True, but it shows the flexibility of one line commands ( I love the semi-colon) and saves us an extra step when we load it into our Mac ~/.bash_profile file.
Aliases also allow us to use variables, you just have to remember to single quote and not double quote the command. Otherwise it will resolve the variable when you set the alias.
$ pwd
/Users/seth
$ alias shellfu="echo O Canada! Our $HOSTNAME and native $PWD; echo True patriot love in all they sons $SHELL"
$ shellfu
O Canada! Our HomePC and native /Users/seth
True patriot love in all they sons /bin/bash
$ cd ~/Desktop
$ shellfu
O Canada! Our HomeMac and native /Users/seth
True patriot love in all they sons /bin/bash
So even though we changed the current working directory, our alias is reporting the path that was active when we set the alias. But when we single quote the command:
$ pwd
/Users/seth
$ alias shellfu='echo O Canada! Our $HOSTNAME and native $PWD; echo True patriot love in all they sons $SHELL'
$ shellfu
O Canada! Our HomeMac and native /Users/seth
True patriot love in all they sons /bin/bash
$ cd ~/Desktop
$ shellfu
O Canada! Our HomeMac and native /Users/seth/Desktop
True patriot love in all they sons /bin/bash
Ok, so what have we learned? First, you can use variables in aliases. Secondly, you can use multiple arguments and commands in aliases. Let’s make this even more interesting.
Suppose it’s 2 am. You’ve just gotten word that a host is down on your network. What’s the first thing you do? Personally I ping it.
$ ping -c 3 curlingrocks.ohcanada.com
PING curlingrocks.ohcanada.com (192.168.128.10): 56 data bytes
64 bytes from 192.168.128.10: icmp_seq=0 ttl=128 time=0.991 ms
64 bytes from 192.168.128.10: icmp_seq=1 ttl=128 time=0.558 ms
64 bytes from 192.168.128.10: icmp_seq=2 ttl=128 time=0.403 ms
...
Ok, so I know that 192.168.128.10 is the correct IP address for that server, so DNS is working and the host is responding to pings. I’m not sure what this server does or where it lives on my company network, but it’s really important and the Boss wants it back up ASAP. So what do I do, run some more commands to see what services are running, etc. Probably faster than trying to dig through crummy documentation.
So with my nice little scan alias:
$ alias scan='hping --count 3 --fast --rawip $_; nslookup $_; echo Results
from $HOSTNAME to $_; traceroute $_; nmap -n -A -PN $_'
After I ping it, I can immediately find out lots of other information about the host without having to wait by just typing in “scan”. Now, the reason that the above works, and we don’t have to get into functions like Hal did, is because the last argument in each command is the IP that we want and it doesn’t change. $_ in the last nmap command is actually referring to the last argument of the traceroute command and so on. If this wasn’t the case, we’d have to use a function like Hal showed us or assign our target IP it’s own variable.
$ alias scan='TARGET=($_); echo Results from $HOSTNAME to $TARGET; hping
--count 3 --fast --rawip $TARGET; nslookup $TARGET; traceroute $TARGET;
nmap -n -A -PN $TARGET'
Also remember if you alias your favorite command, and happen to name it something else useful‚ top perhaps. You can always ignore the alias with a backslash.
$ \top
Talk about an easy way to disguise the up’ers!