I'm searching for a solution to a Bash 4 problem I have.
Bash 4 is able to iterate with leading zeros.
For the line:
for i in {001..005}; do echo -n $i" ";done;echo
the output is
001 002 003 004 005
but when I try this:
a="005"; for i in {001..${a}}; do echo $i;done
or something similar, the result is:
{001..005}
What am I missing?
Your problem is the order in which brace expansion and variable expansion are applied. You must force the reverse order:
a=005
eval echo {001..$a}
Brace expansion is performed before any other expansions....
You could use seq instead:
$ a="005"; for i in $(seq -f %03g 001 ${a}); do echo $i;done
001
002
003
004
005
Brace expansion happens very early during expansion (first thing, in fact), before variable expansion. To perform brace expansion on the result of a variable expansion, you need to use eval, but that tends to be clumsy.
The easy way to iterate is to use a counter variable.
for ((i = 1; i < 5; i++)); do echo -n $i" "; done
To add the leading zeroes, you can format the number with printf:
for ((i = 1; i < 5; i++)); do printf "%03d " $i; done
An alternative trick is to count numbers that are a power of ten larger, and strip away the extraneous prefix.
delta=1000
for ((i = $((delta+1)); i < $((delta+5)); i++)); do echo -n "${i#1} "; done
