Bash - how to avoid command "eval set --" evaluating variables

Question

I just write a little bash script for managing multiple parallels ssh commands. In order to parse arguments I use this piece of code : ``` #!/bin/bash # replace long arguments for arg in "$@"; do case "$arg" in --help) args="${args}-h ";; --host|-hS) args="${args}-s ";; --cmd) args="${args}-c ";; *) [[ "${arg:0:1}" == "-" ]] && delim='' || delim="\"" args="${args}${delim}${arg}${delim} ";; esac done echo "args before eval : $args" eval set -- $args echo "args after eval : $args" while getopts "hs:c:" OPTION; do echo "optarg : $OPTARG" case $OPTION in h) usage; exit 0;; s) servers_array+=("$OPTARG");; c) cmd="$OPTARG";; esac done ``` So I can use for instance -s, --host or -hS for the same result. Everything works fine except one thing. If I put a variable in argument it will be evaluated. Explanations ``` ./test.sh -s SERVER -c 'echo $HOSTNAME' ``` `cmd` should be assigned to `echo $HOSTNAME` but because of the `eval set` cmd is in fact assigned to `echo server1` (the value of the var…

Accepted Answer

As you note, `eval` is evil -- and there's no need to use it here.

```
#!/bin/bash

# make args an array, not a string
args=( )

# replace long arguments
for arg; do
    case "$arg" in
        --help)           args+=( -h ) ;;
        --host|-hS)       args+=( -s ) ;;
        --cmd)            args+=( -c ) ;;
        *)                args+=( "$arg" ) ;;
    esac
done

printf 'args before update : '; printf '%q ' "$@"; echo
set -- "${args[@]}"
printf 'args after update  : '; printf '%q ' "$@"; echo

while getopts "hs:c:" OPTION; do
    : "$OPTION" "$OPTARG"
    echo "optarg : $OPTARG"
    case $OPTION in
    h)  usage; exit 0;;
    s)  servers_array+=("$OPTARG");;
    c)  cmd="$OPTARG";;
    esac
done
```

That is to say: When building up a command line, append individual items to an array; you can then expand that array, quoted, without risking either evaluation or undesired behavior via effects of string-splitting, glob expansion, etc.

Bash - how to avoid command "eval set --" evaluating variables

Solution

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