add absolute path option to a command

Question

Given a shell command (let us call it "oldcommand"), is there a simple shell script newcommand.sh which will behave as oldcommand except that it will have a new "-location" option, and for example,

  newcommand -location path -nonfileoption1 x1 -fileoption2 x2 -fileoption3 x3  -nonfileoption4 x4

will execute

 oldcommand  -nonfileoption1 x1 -fileoption2 path/x2 -fileoption3 path/x3  -nonfileoption4 x4

Answer 1

If all you care about is an option at the beginning, that's a couple of lines of script. Parsing the option in an arbitrary place and passing it to the oldcommand requires several lines and some knowledge of which options have values, and which do not.

For the simple case,

#!/bin/sh
[ "$#" -gt 2 && "x$1" = "x-location" ] && cd $2 && shift 2 && exec oldcommand "$@"
newcommand "$@"

For the complicated case, this sounds like something that you could do with getopt (not portable). Further reading:

• Using getopts in bash shell script to get long and short command line options
• How can I use long options with the Bash getopts builtin?

Per discussion with OP, here is the pattern which may be used to simplify the problem: options beginning with "`-fileopt" should have the location option's value prepended. So (no real error checking, and not really handling embedded special characters in the pathnames):

#!/bin/sh
PREP=
if [ "$#" -gt 2 ]
then
    PREP="$2/"
    shift 2
    ARGS=
    while [ "$#" != 0 ]
    do
        case "x$1" in
        (x-fileopt*)
            ARGS="$ARGS $1 ${PREP}$2"
            shift 2
            ;;
        (*)
            ARGS="$ARGS $1"
            shift 1
        esac
    done
    oldcommand $ARGS
else
    oldcommand "$@"
fi

Answer 2

This smells a lot like an XY problem. If you want oldcommand to treat all relative file names as relative to a different directory, change the current directory!

(cd path && oldcommand  -nonfileoption1 x1 -fileoption2 x2 -fileoption3 x3  -nonfileoption4 x4)

The parentheses ensure that the directory change is local: the next command will be executed in the original directory.

If you want to package this in a script:

#!/bin/sh
cd "$1" && shift && "$@"

Usage:

run-in path oldcommand  -nonfileoption1 x1 -fileoption2 x2 -fileoption3 x3  -nonfileoption4 x4

For command line usage, though, a temporary directory change might be more convenient. It requires a smidgen more typing, but it allows filename completion to work out of the box. (You can make completion work for the wrapper script method, but you'll need to define a completion function for the run-in script.)

cd path
oldcommand  -nonfileoption1 x1 -fileoption2 x2 -fileoption3 x3  -nonfileoption4 x4
cd -

or

pushd path
oldcommand  -nonfileoption1 x1 -fileoption2 x2 -fileoption3 x3  -nonfileoption4 x4
popd

Compared to what you're asking, this makes all relative file names relative to path, not just the ones passed on the command line but any relative file name that oldcommand uses internally. This also assumes that oldcommand doesn't itself change to a different directory. Both assumptions are met by many commands.

Answer 3

opt()
    case ${1##*:*}:${#2} in
    (--:*) ! x=$((x-2))  ;;
    (-nonfileoption:[!0]*) p=;;
    (-fileoption:[!0]*)    p=\$2/;;
    (*:0)  eval $"{$x"':?Bad option::arg: "$1::$2"}';;
    (*)    eval $"{$((x-1))"':?Bad option: "$1"}'
    esac

[ " -location" = " $1" ] && x=2 parm= &&
while  [ "$#" -ge "$((x+=2))" ]
do     eval 'opt  "${'"$((x-1))"'}" "${'"$x}\"" ||
          until [ "$x" -eq "$#" ] && break 2
          do    parm=$parm' "${'$((x+=1))}\"
          done
       parm=$parm' "${'$((x-1))'}"  "'$p\${$x}\"
done&& eval "set -- $parm"