Adding a zero to single digit variable

Question

Trying to add a zero before the varaible if it's less than 10 and create said directory. I can't seem to get the zero to add correctly. Keeps resulting in making 02.1.2011, 02.2.2011 etc,etc.

i=0 for i in {01..31} do     if $i > 10         then             mkdir $path/02.0$i.2011         else                 mkdir $path/02.$i.2011     fi done 

Answer 1

You can replace the whole lot with:

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

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}; done 08 09 10 11 

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} ; done 08 09 10 11