Shell Programming and Scripting

Bourne shell does not have ${var%pattern}. If you think you're using bourne shell, you're probably on Linux (sh points to bash).

Can you point to the docs saying that the pattern is actually a regexp? I doubt it... and I can't find it in the man pages.

FreeBSD sh , and I don't have bash.

Thank you all for your help

On Solaris, using /bin/sh (definitely a good old-fashioned Bourne shell):

Code:

#!/bin/sh
x="hellothere"
y=${x%.*.?}
echo "x is: %x, y is: $y"

Gives:
bad substitution

Simplifying, by changing the ${x%.*.?} to ${x%there} gives the same response.

If I use ksh:

Code:

#!/bin/ksh
x="hellothere"
y=${x%there}
echo "x is: %x, y is: $y"

I properly get: x is: hellothere, y is: hello. Bash works, as well. Looks like it's pattern matching only.

But assuming that regular expressions are supported, I'll test

Code:

#!/bin/sh
x="hellothere"
y=${x%..*}
echo "x is: %x, y is: $y"

...This should match "1 of anything, followed by 0 or more instances of anything." That is, y should be completely empty. Testing with sh, ksh, and bash:...So it doesn't work. If I assume the variable substitution is a pattern instead, that is I assume y=${x%..*} means "y equals x but remove a literal dot followed by a literal dot followed by anything (or nothing)", then let me change x to be something that such a pattern should match:

Code:

x="front..hellothere"

In this case, y should be "front". The results are:...That is, both ksh and bash work properly.


This shows that for Bourne shell, ksh88, and bash, this variable construct uses pattern matching, not regular expressions.

See Regular Expressions - a Simple User Guide for more information about regular expressions. See also The Regex Coach - interactive regular expressions for a very useful (Windows-based) tool.

There's a great explanation and examples of Korn shell variable expansion here.

InformIT: Variables and Parameters in the Korn Shell > Variable Expansion