Adding a zero to single digit variable

You can replace the whole lot with:

for day in 0{1..9} {10..31} ; do    mkdir ${path}/02.${day}.2011done

while still not having to start up any external processes (other than what may be in the loop body).

That's probably not that important here since mkdir is not one of those things you tend to do a lot of in a tight loop but it will be important if you write a lot of your quick and dirty code in bash.

Process creation is expensive when you're doing it hundreds of thousands of times as some of my scripts have occasionally done :-)

Example so you can see it in action:

pax$ for day in 0{8..9} {10..11}; do echo ${day}; done08091011

And, if you have a recent-enough version of bash, it will honor your request for leading digits:

A sequence expression takes the form {x..y[..incr]}, where x and y are either integers or single characters, and incr, an optional increment, is an integer.

When integers are supplied, the expression expands to each number between x and y, inclusive.

Supplied integers may be prefixed with 0 to force each term to have the same width. When either x or y begins with a zero, the shell attempts to force all generated terms to contain the same number of digits, zero-padding where necessary.

So, on my Debian 6 box, with bash version 4.1.5:

pax$ for day in {08..11} ; do echo ${day} ; done08091011

You can use

$(printf %02d $i)

To generate the numbers with the format you want.

for i in $(seq 0 1 31)do    mkdir $path/02.$(printf %02d $i).2011done

Better:

for i in $(seq -f %02g 1 31)do    mkdir "$path/02.$i.2011"done

Or even:

for i in {01..31}do    mkdir "$path/02.$(printf "%02d" $i).2011"done