Regex in KornShell

Question

I am trying to check whether a variable is exactly two numbers but I can not seem to figure it out.

How do you do check regular expressions (regex) in KornShell (ksh

Answer 1

Ksh has supported limited extended patterns since ksh88, using the

special '(' pattern ')'

syntax.

In ksh88, the 'special' character prefixes change the number of matches expected:

'*' for zero or more matches
'+' at least one match
'@' for exactly one match
'?' for zero or one matches
'!' for negation

In ksh93, this was expanded with

'{' min ',' max '}'

to express an exact range:

for w in 1423 12 "" abc 23423 9 33 3  333
do
  [[ $w == {1,3}(\d) ]] && print $w has between 1 and three digits
  [[ $w == {2}(\d) ]] && print $w has exactly two digits
done

And finally, you can have perl-like clutter with '~', which introduces a whole new class of extensions,including full regular expressions with:

'~(E)( regex )'

More examples can be found in Finnbarr P. Murphy's blog