Tag: shell

Categories
unix

Don’t call it test

There are quite a few names to avoid in your scripts. Even if there are not reserved-words, keep away !

I’ll start with test

cd $HOME/bin
vi test
echo hello world
chmod +x test
./test
hello world

The problem is that it may break your other scripts

$ ssh localhost test 1 = 2 && echo WHAT???
hello world
WHAT???

And it may break sooner or later, depending on your OS / version / default shell / default path / others.

There are quite a few filenames you should not use, like test, date, time, hostname, mail, view, touch, sort and make. The command type lists some of those as reserved word, shell builtin, tracked alias, shell keyword. But again it is not consistent over Unix flavors.


$ uname -sr; type date
SunOS 5.10
date is /usr/bin/date
$ uname -sr; type date
Linux 2.6
date is a tracked alias for /bin/date

Your sysadmin may also alias things for colors and safety in the common profile: for instance vi, ls, rm. But if it annoys you, then use \vi instead of vi.

Categories
linux unix

To bash or not to bash

I have been inspired by Chen to talk about bash…

I have been using ksh for many years, and I mean ksh88 not ksh93. The main reason is, I want my script to run the same way in any Unix flavor.

ksh93 has never been too much popular. I used it a few time to sleep half a second


echo sleep 0.5| /usr/dt/bin/dtksh

ksh has a lot of nice features. I just used one of them in my script :

$ typeset -u name
$ read name?"Enter your name : "
Enter your name : Laurent
$ echo $name
LAURENT

Way easier to force a variable to be uppercase rather than using echo|tr etc

Bash has some nice features too, but unfortunately every OS release come with a different bash version, which is the same pain as perl when you want to write a script that last for a decade or two.

Ok, just4fun

$ mkdir -p {a..z}/{1..9}
... create directories a/1 a/2 ... z/8 z /9
$ [[ text =~ t..t ]]
... check if text matches regular expression t..t
$ echo ${text/pattern/string}
... replace pattern by string

The first two commands require bash3, the last is just fine with bash2.

Have fun shell-scripting 🙂