I'm working on a simple bash script that fixes a duplicate naming issue on a retropie.

The script itself grabs any name that is mentioned more than once in a gameslist.xml file, then stores those in an array for later use.

I end up looping over this array in indexes like so:

pi@retropie:~ $ for game in ${game_array[@]:0:10} ; do echo $game; done

which pulls the 1st to the 10th element (i.e. ${game_array[9]})
however the output gets joined to one line:

pi@retropie:~ $ for game in ${game_array[@]:0:10} ; do echo $game; done

R.B.I. Baseball '94 World Series Baseball '95 Mega Games 1 Bill Walsh College Football T2: The Arcade Game Sonic & Knuckles + Sonic the Hedgehog Sega Top Five Pyramid Magic Tecmo Super Baseball Super Chinese Tycoon

But if I loop over the entire array, it outputs on new lines as expected:

pi@retropie:~ $ for game in ${game_array[@]}; do echo $game; done | head -10

R.B.I. Baseball '94

World Series Baseball '95

Mega Games 1

Bill Walsh College Football

T2: The Arcade Game

Sonic & Knuckles + Sonic the Hedgehog

Sega Top Five

Pyramid Magic

Tecmo Super Baseball

Super Chinese Tycoon

the field seperator has been set to new line with IFS='$n' which is why the second one works, but I can't for the life of me figure out why it isn't with the first one?

here's the full test script for context:

#!/bin/bash



user_input=$1

while [ -z "$user_input" ]; do

        echo "please enter the name of the system you want to fix the game list for"

        echo "(as it is labelled in /home/pi/RetroPie/roms)"

        read -r user_input

done



ls "/home/pi/RetroPie/roms/$user_input" >/dev/null 2>&1



if  [ "$?" -ne 0 ]; then

        echo "this doesn't appear to be a system installed here. exiting."

        exit 1

fi



games_to_fix()

{

        IFS=$'n'

        console=$1

        filepath="/opt/retropie/configs/all/emulationstation/gamelists/$console/gamelist.xml"

        game_array=($(fgrep "<name>" "$filepath" | sort | uniq -c | sort -rn | awk  '$1 > 1 {print $0}'| cut -d ">" -f 2 | cut -d "<" -f 1))

        number_to_fix=($(fgrep "<name>" "$filepath" | sort | uniq -c | sort -rn | awk  '$1 > 1 {print $1}'))

}



get_new_name()

{

        mYpath=$1

        new_name=$(echo $mYpath | cut -d ">" -f 2 | cut -d "<" -f 1 | sed -e 's/.///g' | sed -e 's/.7z//g')

}



games_to_fix $user_input



IFS=$'n'

index=0

for i in ${number_to_fix[@]}; do

        loop=1

        for game in ${game_array[@]:$index:$i}; do

        #       for ind in $(eval echo {1..$i}); do

                line_number=$(fgrep -n "<name>$game</name>"  $filepath | awk '{print $1}' | cut -d : -f 1 | sed -e "${loop}q;d")

                path_line_number=$(expr $line_number - 1 )

                path=$(sed "${path_line_number}q;d" $filepath | cut -d : -f 2)

                get_new_name "$path"

                sed -i "${line_number}s/$game/$new_name/g" $filepath

                ((loop++))

        done

        index=$(expr index + $i);

done

In brief: you should use quotes around array expansions like that, unless you explicitly want field/word splitting. "$@" expands each positional parameter to a separate word, and similarly so does "${a[@]}". By extension, that should work in the same way for "${a[@]:0:2}".

That said, it still seems like an inconsistency in Bash, and what you used should work in your case (since there are no glob characters in the values, and field splitting is taken care of by IFS being set properly).

Taking the full array works:

$ IFS=$'n'

$ a=("foo bar" "asdf ghjk")

$ printf "%sn" ${a[@]}

foo bar

asdf ghjk

Slicing it doesn't work for an array, but works for $@:

$ printf "%sn" ${a[@]:0:2}

foo bar asdf ghjk



$ set -- "aa bb" "cc dd"

$ printf "%sn" ${@:1:2}

aa bb

cc dd

It does work in ksh and zsh, which sort of underlines Bash being inconsistent here _{(zsh of course would have its own syntax for the equivalent)}:

$ ifs=$'n' ksh -c 'IFS="$ifs"; a=("foo bar" "asdf ghjk"); printf "%sn" ${a[@]:0:2}'

foo bar

asdf ghjk

$ ifs=$'n' zsh -yc 'IFS="$ifs"; a=("foo bar" "asdf ghjk"); printf "%sn" ${a[@]:0:2}'

foo bar

asdf ghjk

The quoted version works in Bash, too, and is better when you just want the values as-is, since you don't need to depend on IFS. The default IFS works fine here even though the array elements have spaces:

$ unset IFS                         # uses default of $' tn'

$ printf "%sn" "${a[@]:0:2}"

foo bar

asdf ghjk

It looks as though the unquoted ${a[@]:0:2} joins the elements with spaces, a bit like what happens in Bash in contexts where word-splitting doesn't happen (e.g. str=${a[@]}). And then it tries to split the result with IFS, as usual. E.g. here, it splits on the newline in the middle of the second array element:

$ IFS=$'n'

$ a=("foo bar" $'newnline' "asdf ghjk");

$ printf ":%sn" ${a[@]:0:3}

:foo bar new

:line asdf ghjk

As said above, you really should use the quotes around array expansions in most cases, though still, one would assume ${a[@]:n:m} would result in multiple words, just like ${a[@]} does.

The behaviour here seems present in Bash 4.4.12(1)-release and 5.0.0(1)-alpha. I posted a bug report about it.

quote
quote

Quote

Quote

Quote!!

This works:

$ game_array=("foo bar" "baz" "bam foo" "bar")



$ for game in "${game_array[@]:0:10}" ; do echo "$game"; done

foo bar

baz

bam foo

bar