Re: invoke tilde expansion on quoted string

[Freddy Vulto]

This is used in the bash-completion package:

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# Expand variable starting with tilde (~)
# We want to expand ~foo/... to /home/foo/... to avoid problems when
# word-to-complete starting with a tilde is fed to commands and ending
# up quoted instead of expanded.
# Only the first portion of the variable from the tilde up to the first
# slash (~../) is expanded.  The remainder of the variable, containing
# for example a dollar sign variable ($) or asterisk (*) is not
# expanded.
# Example usage:
#
#    $ v="~"; __expand_tilde_by_ref v; echo "$v"
#
# Example output:
#
#       v                  output
#    --------         ----------------
#    ~                /home/user
#    ~foo/bar         /home/foo/bar
#    ~foo/$HOME       /home/foo/$HOME
#    ~foo/a  b        /home/foo/a  b
#    ~foo/*           /home/foo/*
#  
# @param $1  Name of variable (not the value of the variable) to expand
__expand_tilde_by_ref() {
    # Does $1 start with tilde (~)?
    if [ "${!1:0:1}" = "~" ]; then
        # Does $1 contain slash (/)?
        if [ "${!1}" != "${!1//\/}" ]; then
            # Yes, $1 contains slash;
            # 1: Remove * including and after first slash (/), i.e. "~a/b"
            #    becomes "~a".  Double quotes allow eval.
            # 2: Remove * before the first slash (/), i.e. "~a/b"
            #    becomes "b".  Single quotes prevent eval.
            #       +-----1----+ +---2----+
            eval $1="${!1/%\/*}"/'${!1#*/}'
        else 
            # No, $1 doesn't contain slash
            eval $1="${!1}"
        fi
    fi
} # __expand_tilde_by_ref()

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Freddy Vulto
http://fvue.nl