LinuxQuestions.org - [SOLVED] how can I improve this algorithm in bash

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how can I improve this algorithm in bash

basically I have a directory with files, and I want to output current file, previous file, next file. So here's my algorithm

Code:

for ((i=0; i<$total; i++)); do

 thisfile=${files[i]}

 if [ $i -eq 0 ]; then

  previousfile=""

 elif [ $i -eq $((total-1)) ]; then

  nextfile=""

 else

  previousfile=${files[$((i-1))]}

  nextfile=${files[$((i+1))]}

 fi

 echo $previousfile $thisfile $nextfile

done

Maybe you can avoid superfluous assignments:

Code:

for ((i=0; i<$total; i++))

do

  [[ $i == 0 ]] || echo -n "${files[$((i-1))]} "

  echo ${files[i]} ${files[$((i+1))]}

done

If you are going to use (()) for the for statement, why not use them for the rest of your arithmetic expressions?

Code:

for ((i=0; i < total; i++)); do

 thisfile=${files[i]}

 if (( i == 0 )); then

  previousfile=""

 elif (( i == total - 1 )); then

  nextfile=""

 else

  previousfile=${files[i-1]}

  nextfile=${files[i+1]}

 fi

 echo $previousfile $thisfile $nextfile

done

I have highlighted in red all the changes I made.

I am curious to the output when i = 0, ie nextfile is not calculated, so strictly speaking, unless total is 1, this should
have a value.

Lastly, when the output shows a single file name (or any for that matter), how do you know which position this name is in?
This perhaps picky, but if the script is not just for you (or you run it in a months time and forget) it may
be tricky for a user to tell exactly what they are seeing without any labels ... just a thought ;)

Quote:

Originally Posted by grail (Post 5138420)

If you are going to use (()) for the for statement, why not use them for the rest of your arithmetic expressions?

Code:

for ((i=0; i < total; i++)); do

 thisfile=${files[i]}

 if (( i == 0 )); then

  previousfile=""

 elif (( i == total - 1 )); then

  nextfile=""

 else

  previousfile=${files[i-1]}

  nextfile=${files[i+1]}

 fi

 echo $previousfile $thisfile $nextfile

done

yeah, that's basically the same way I have it. I did it to make an array of pictures and create webpages with links to next and previous page.
So if you look at my script above, instead of echo to stdout I would call another function that has some html code and create a page for every picture with links to previous and next. Hope it makes sence.

Well whilst this may be an improvement on the current code, I think colucix has presented the best option, ie use the array you have created which removes most if not all the if / else requirements