16
[GUIDANCE] "For" in Bash (programming.dev)
submitted 10 months ago by to c/linux@programming.dev
15 comments fedilink hide all child comments
 

Edit: SOLVED. Thank you all for your incredible insights! All of you helped me improve my code and knowledge! Special thanks to @Quibblekrust@thelemmy.club who just NAILED it. :)

I'm playing around with Bash just to learn.

LIST=$(ls); for i in $LIST; do echo "I found one!"; done

The variable "i" could literally be anything, as long as it doesn't have a special meaning for Bash, in which case I'd have to escape it, right? Anyway, my real question is: how does do (or rather the whole for-expression) know that "i" here means "for every line/item that ls outputs"? The above one liner works great and writes "I found one!" the number of times corresponding to the number of lines or items that ls outputs. But I would like to understand why it worked...

I'm a complete beginner at both Bash and C, but I understand some basic concepts.

you are viewing a single comment's thread
view the rest of the comments
[–] 3 points 10 months ago (4 children)

Wouldn't for i in "$LIST"; just result in a single loop iteration with $i being the entirety of $LIST?

  • permalink
  • fedilink
  • source
  • parent
  • hideshow 4 child comments
    •
  • [–] 4 points 10 months ago (3 children)

    It would not, as @Quibblekrust@thelemmy.club explained in their comment (which I neglected to include in my explanation), Bash uses a special variable called IFS when executing for loops like this. IFS stands for Input Field Separators, and is a list of one of each type of whitespace (tab, space, and newline), and uses these as separators automatically.

    So instead of taking that whole ls output as one string of text, the for loop automatically separates it into an iterable list of strings using the newline separator.

  • permalink
  • fedilink
  • source
  • parent
  • hideshow 3 child comments
    •
  • [–] 6 points 10 months ago (1 child)

    I'm pretty sure that IFS does not apply to quoted strings since word splitting happens before the quote removal (see Shell Expansion).

    $ ( files=$(ls); IFS=$'\n' ; for x in $files; do echo $x; done )
file a.txt
file b.txt
plainfile.txt

$ ( files=$(ls); IFS=$'\n' ; for x in "$files"; do echo $x; done )
file a.txt file b.txt plainfile.txt
  • permalink
  • fedilink
  • source
  • parent
  • hideshow 1 child comment
    •