Padding zeros in a string
BashBash Problem Overview
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?
Bash Solutions
Solution 1 - Bash
Use backticks 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 $n variable substitution you used before.
Solution 2 - Bash
Seems you're assigning the return value of the printf command (which is its exit code), you want to assign the output of printf.
bash-3.2$ n=1
bash-3.2$ n=$(printf %03d $n)
bash-3.2$ echo $n
001
Solution 3 - Bash
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
Solution 4 - Bash
to avoid context switching:
a="123"
b="00000${a}"
c="${b: -5}"
Solution 5 - Bash
n=`printf '%03d' "2"`
Note spacing and backticks
Solution 6 - Bash
As mentioned by noselad, please command substitution, i.e. $(...), is preferable as it supercedes backtics, i.e. `...`.
Much easier to work with when trying to nest several command substitutions instead of escaping, i.e. "backslashing", backtics.
Solution 7 - Bash
This is in response to an answer given by cC Xx.
It will work only until a's value less is than 5 digits.
Consider when a=12345678.
It'll truncate the leading digits:
a="12345678"
b="00000${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