The following command:
a=$(expr "$a" + 1)
adds 1 to the variable a.
The following command, for "$a" equal to either /usr/abc/file or
just file:
expr $a : '.*/\(.*\)' \| $a
returns the last segment of a pathname (that is, file).
Applications should avoid the character '/' used alone as an
argument; expr may interpret it as the division operator.
The following command:
expr "//$a" : '.*/\(.*\)'
is a better representation of the previous example. The addition
of the "//" characters eliminates any ambiguity about the
division operator and simplifies the whole expression. Also note
that pathnames may contain characters contained in the IFS
variable and should be quoted to avoid having "$a" expand into
multiple arguments.
The following command:
expr "X$VAR" : '.*' - 1
returns the number of characters in VAR.
