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Another ^A bug


From: Martijn Dekker
Subject: Another ^A bug
Date: Tue, 20 Nov 2018 18:24:04 +0100
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.11; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

That ^A / $'\1' character just keeps causing trouble...

This is a bug with IFS. Including a $'\1' character anywhere in IFS causes expansions in shell assignments to discard that character.

$ bash -c "c=$'Y\1Y';
    for IFS in $'\1' $'\2' $'x\1' $'x\2' $'\1x' $'\2x'; do
        v=X\${c}X;
        printf %s \"\$v\" | od -a | awk 'NR==1 { \$1=\"\"; print }';
    done"

Output on bash 4.4 and current git:
 X Y Y X
 X Y soh Y X
 X Y Y X
 X Y soh Y X
 X Y Y X
 X Y soh Y X

Expected output, on bash 4.3 and earlier, and all other shells:
 X Y soh Y X
 X Y soh Y X
 X Y soh Y X
 X Y soh Y X
 X Y soh Y X
 X Y soh Y X

Note that quoting the assigned value is an effective workaround. But in shell grammar, IFS should never have any influence on true shell assignments (as opposed to assignment-arguments) and quoting expansions should not be necessary. (This paragraph is included to pre-empt readers who would reply "just quote everything". Yes, I know. It's still a bug.)

Thanks,

- Martijn



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