Infinite loop? Seemingly caused by innocuous code

Question

I have this bash function:

botch_get_prev_cd(){
    local dr=$(declare -f cd);
    local dr_trimmed="$(tr -d "$dr")"

    if [[ "$dr_trimmed" != *"run_botch"* ]]; then
        definition_prev_cd="prev_$dr"
        echo "$definition_prev_cd";
        eval "${definition_prev_cd}"
        unset definition_prev_cd  # clean up, no reason to leave this string around
        export -f prev_cd
    fi
}

when I call it, my routine freezes, appears like it's just going into an infinite loop.

When I change my code to this, it works:

botch_get_prev_cd(){
    local dr=$(declare -f cd);

    if [[ "$dr" != *"run_botch"* ]]; then
        definition_prev_cd="prev_$dr"
        echo "$definition_prev_cd";
        eval "${definition_prev_cd}"
        unset definition_prev_cd  # clean up, no reason to leave this string around
        export -f prev_cd
    fi
}

so maybe I don't need to trim the whitespace to check for matching characters? I hope so, because the first function doesn't seem to work, not sure why it seems to go into an infinite loop..

Answer 1

This isn’t an infinite loop, it’s

tr -d "$dr"

waiting for input.

I’m not sure exactly what you’re trying to do there; if you want to use tr to delete characters from a value stored in a variable, you need to give it the value:

tr -d " " <<<"$dr"

would delete all spaces from the value stored in dr.

Answer 2

One problem with your code is this line

local dr_trimmed="$(tr -d "$dr")"

I assume that $dr is a range of characters for tr to delete from stdin, but you have forgotten to provide tr with any data to process. So it's sitting there waiting for some.