Subj.
On my ipad I was download tar from ruby-Lang.org, then untar it. & when I try to ./configure it I receive this error:
./configure: line 426: expr: command not found
./configure.lineno: line 426: expr: command not found
./configure.lineno: line 426: expr: command not found
....
....
....
What's mean this error? I google it but not found anything.