I'm writing a bash script to get some podcasts. The problem is that some of the podcast numbers are one digits while others are two/three digits, therefore I need to pad them to make them all 3 digits.
I tried the following:
n=1 n = printf %03d $n wget http://aolradio.podcast.aol.com/sn/SN-$n.mp3 but the variable 'n' doesn't stay padded permanently. How can I make it permanent?
Use command substitution to assign the result of the printf command:
n=1 wget http://aolradio.podcast.aol.com/sn/SN-$(printf %03d $n).mp3 EDIT: Note that I removed one line which was not really necessary. If you want to assign the output of 'printf %...' to n, you could use
n=$(printf %03d $n) and after that, use the $n variable substitution you used before.
wget $(printf http://aolradio.podcast.aol.com/sn/SN-%03d $n.mp3, $n). Just put the whole URL in the printf statement.
Seems you're assigning the return value of the printf command (which is its exit code), you want to assign the output of printf.
bash-3.2$ n=1 bash-3.2$ n=$(printf %03d $n) bash-3.2$ echo $n 001 Attention though if your input string has a leading zero!
printf will still do the padding, but also convert your string to hex octal format.
# looks ok $ echo `printf "%05d" 03` 00003 # but not for numbers over 8 $ echo `printf "%05d" 033` 00027 A solution to this seems to be printing a float instead of decimal.
The trick is omitting the decimal places with .0f.
# works with leading zero $ echo `printf "%05.0f" 033` 00033 # as well as without $ echo `printf "%05.0f" 33` 00033 
to avoid context switching:
a="123" b="00000${a}" c="${b: -5}" 
while [ "${s:0:1}" = '0' ]; do s=${s:1}; done
a="123456"; [[ ${#a} -lt 5 ]] && a="00000${a}" && a="${a: -5}"; echo "$a"
printf. printf is a built-in function in bash, as one can check via man bash.As mentioned by noselad, please command substitution, i.e. $(...), is preferable as it supercedes backtics, i.e. `...`.
Much easier to work with when trying to nest several command substitutions instead of escaping, i.e. "backslashing", backtics.
This is in response to an answer given by cC Xx. It will work only until a's value less is than 5 digits.
Consider when a=12345678. It'll truncate the leading digits:
a="12345678" b="00000${a}" c="${b: -5}" echo "$a, $b, $c" This gives the following output:
12345678, 0000012345678, 45678 Putting an if to check value of a is less than 5 digits and then doing it could be solution:
if [[ $a -lt 9999 ]] ; then b="00000${a}" ; c="${b: -5}" ; else c=$a; fi 
Just typing this here for additional information.
If you know the number of zeroes you need, you can use the string concatenation:
let pad="0" pad+=1 echo $pad # this will print 01 