Bash interpolation

Khannie

Ok, this question is best explained with an example....

I want this command:

for i in [0-9]; do echo $i; done

to produce:

0
1
2
3
4
5
6
7
8
9

instead, it produces:

[0-9]

Is there any way (outside a while loop) to achieve this?

If I do:

ls *[0-9]*

it is interpolated correctly (i.e. any filename with a number in it is listed).

stereo_steve

for i in {0..9}; do echo $i; done

will work, its called a brace expansion if you want to google it.

I don't know why your command won't work?

brianmc

Khannie wrote: »

If I do:

ls *[0-9]*

it is interpolated correctly (i.e. any filename with a number in it is listed).

Outside of some other context this is exactly what [0-9] does. i.e. filename matching.

Doesn't Bash support some class of artihmetic for loop?

for ((i=0; i<10; i++))
do
    echo $i
done

Khannie

stereo_steve wrote: »

for i in {0..9}; do echo $i; done

will work, its called a brace expansion if you want to google it.

I don't know why your command won't work?

This is exactly what I was looking for. Cheers. I guess I was used to the [0-9] style from regular expressions and that appears to be what they're used for by bash too.

niallb

Not an answer to your expansion question,
but a solution to your required output is to use the seq command

seq 0 1 9
will give you the number from 0 to 9 in increments of 1.
If you're going to more digits, -w will zero pad the output,
so seq -w 0 1 10 will give you 00 to 10 rather than 0 to 10.

Backticking it will get you closest to your original logic.

for i in `seq 0 1 9`
do
echo $i
done

The reason your first example doesn't work is that while bash will expand the expression, echo won't.

brianmc

niallb wrote: »

The reason your first example doesn't work is that while bash will expand the expression, echo won't.

You're correct that echo doens't expand anything. It prints out whatever arguments it receives. It has received one argument only though... the "word" "[0-9]". Bash hasn't expanded anything either.

Given that there's no other context in that line, if there had been filenames in the current directory of 0 or 1 or 2 or any single digit it would have been expanded to the list of those.