Question

can anybody explain why the following bash code involving compound operators is not behaving as expected? basically, nothing enters the if statement inside the for loop but i am passing it correct parameters that should return something by running:
./my_bash_script 20100101 20120101

dates.txt is a list of all days since 2000

#!/bin/bash

old_IFS=$IFS
IFS=$'\n'
lines=($(cat dates.txt)) # array
IFS=$old_IFS

for (( i=1; i<${#lines[@]}; i++ ))
do
  if [[ ${line[$i]} -ge $1 && ${line[$i]} -le $2 ]]; then
      echo 0 > ${line[$i]} # redirect to file
      echo ${line[$i]}
  fi
done

Answer 1

The problem is that you’ve declared an array named lines, but then you try to access it as though it were named line. You need to change every occurrence of ${line[$i]} to ${lines[$i]}.

Better yet, you can dispense with the arithmetic for-loop, and write:

for line in "${lines[@]}" ; do

which will let you refer to the line as $line or "$line" rather than as ${lines[$i]}.

(By the way, how come you have that logic to modify $IFS? It seems like its default value would work just as well.)