word splitting

http://mywiki.wooledge.org/BashPitfalls highlights the “broken legacy misfeature” word splitting.

Before a bash command is executed the arguments are processed. After most of other processing is done, any argument containing whitespace is split into separate arguments, unless the whitespace is somehow protected. This is the word splitting feature and it is one big source of trouble.

Users tend to believe that in the line

cmd $A

there is a command with one argument. But in truth the number of arguments cannot be seen unless you know how the value of A was defined.

This is somehow unnecessary. Tcl is similar to bash as is does not really has types, uses polish notation, and variable are referenced by putting a $ in front of the variable name. But when you refer a variable in tcl you always get one value. If the value is a list and if you want pass its entries as separate arguments you have to split it up explicitly.

All together tcl solves the distinctions of whitespace that separates items and whitespace that belongs to items pretty well. The tcl way of solving it cannot be added to bash as it uses curly brackets that are, as any other brackets, already loaded with semantics in bash. Nonetheless, its strange that the prevailing scripting language affords to make people stumble on this issue.


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s

%d bloggers like this: