numeric for-loop and string for-loop

numeric for-loop and string for-loop

[Peng Yu]

Hi,

The following zsh and bash code generate different resutls. I feel the
bash convention is better.

To make the second i as string in zsh, what is the best solution so
that the minimum amount of code is changed. (I'd rather not to change
the second `i` to some other variable name as each for-loop should be
independent from each other, and should not know each other to make
the code work.). Thanks.

$ cat main.sh
#!/usr/bin/env zsh
# vim: set noexpandtab tabstop=2:

set -v
for ((i=0;i<2;++i))
do
    echo $i
done

declare -p i
for i in a b
do
    declare -p i
done


$ cat main.bash
#!/usr/bin/env bash
# vim: set noexpandtab tabstop=2:

set -v
for ((i=0;i<2;++i))
do
    echo $i
done

declare -p i
for i in a b
do
    declare -p i
done


$ ./main.sh
for ((i=0;i<2;++i))
do
    echo $i
done
0
1

declare -p i
typeset -i i=2
for i in a b
do
    declare -p i
done
typeset -i i=0
typeset -i i=0


$ ./main.bash
for ((i=0;i<2;++i))
do
    echo $i
done
0
1

declare -p i
declare -- i="2"
for i in a b
do
    declare -p i
done
declare -- i="a"
declare -- i="b"

-- 
Regards,
Peng

Re: numeric for-loop and string for-loop

[Peter Stephenson]

On Mon, 2018-12-03 at 07:56 -0600, Peng Yu wrote:
> To make the second i as string in zsh, what is the best solution so
> that the minimum amount of code is changed.

If you want to turn an integer into a string,

declare +i i

will work.

pws

Re: numeric for-loop and string for-loop

[Mikael Magnusson]

% a=5+5 b=2\*3
% typeset -i i
% for i in a b; do declare -p i; done; declare -p a b
typeset -i i=10
typeset -i i=6
typeset a=5+5
typeset b='2*3'

If this is not what you want, you can use unset i before each loop.

On 12/3/18, Peng Yu <pengyu.ut@gmail.com> wrote:
> Hi,
>
> The following zsh and bash code generate different resutls. I feel the
> bash convention is better.
>
> To make the second i as string in zsh, what is the best solution so
> that the minimum amount of code is changed. (I'd rather not to change
> the second `i` to some other variable name as each for-loop should be
> independent from each other, and should not know each other to make
> the code work.). Thanks.
>
> $ cat main.sh
> #!/usr/bin/env zsh
> # vim: set noexpandtab tabstop=2:
>
> set -v
> for ((i=0;i<2;++i))
> do
>     echo $i
> done
>
> declare -p i
> for i in a b
> do
>     declare -p i
> done
>
>
> $ cat main.bash
> #!/usr/bin/env bash
> # vim: set noexpandtab tabstop=2:
>
> set -v
> for ((i=0;i<2;++i))
> do
>     echo $i
> done
>
> declare -p i
> for i in a b
> do
>     declare -p i
> done
>
>
> $ ./main.sh
> for ((i=0;i<2;++i))
> do
>     echo $i
> done
> 0
> 1
>
> declare -p i
> typeset -i i=2
> for i in a b
> do
>     declare -p i
> done
> typeset -i i=0
> typeset -i i=0
>
>
> $ ./main.bash
> for ((i=0;i<2;++i))
> do
>     echo $i
> done
> 0
> 1
>
> declare -p i
> declare -- i="2"
> for i in a b
> do
>     declare -p i
> done
> declare -- i="a"
> declare -- i="b"
>
> --
> Regards,
> Peng
>


-- 
Mikael Magnusson

Re: numeric for-loop and string for-loop

[Mikael Magnusson]

On 12/3/18, Mikael Magnusson <mikachu@gmail.com> wrote:
> % a=5+5 b=2\*3
> % typeset -i i
> % for i in a b; do declare -p i; done; declare -p a b
> typeset -i i=10
> typeset -i i=6
> typeset a=5+5
> typeset b='2*3'
>
> If this is not what you want, you can use unset i before each loop.

In fact, bash will act the same way as zsh if you say "typeset -i i",
the only difference is that zsh will create parameters as integers in
a mathematical context if they did not previously exist. In other
words, your zsh script will also "work" if you do "typeset i" before
the first loop, because then it already exists when you get to the
math loop.

-- 
Mikael Magnusson