prepend_path.sh

#!/bin/sh
prepend_path() {
    if [ -z "$1" ] || [ -z "$2" ]; then
        echo "usage: prepend_path <directory> <env.var>"
        echo "e.g. prepend_path ~/.local/bin PATH"
        echo "received: prepend_path $@"
        return 1
    fi
    local dir="$1"
    local env_var="$2"
    if [ ! -d "$dir" ]; then
        echo "\"$dir\" cannot be prepended to \"$env_var\" because it is not a directory."
        return 1
    fi
    # Remove directory if it already exists in the variable
    if eval "echo \$$env_var | tr ':' '\\n' | grep -xqF \"$dir\""; then
        echo "\"$dir\" already present in \"\$$env_var\", moving to front..."
        # colon2newline, reove $dir, remove trailing newline, then newline2colon
        eval "export \$env_var=\$(echo \"\$$env_var\" | tr ':' '\\n' | grep -vxF \"$dir\" | sed -Ez 's/\n+$//' | tr '\\n' ':')"
    fi
    if eval "[ -z \"\$$env_var\" ]"; then
        cmd="export $env_var=\"$dir\""
    else
        cmd="export $env_var=\"$dir:\$$env_var\""
    fi
    eval $cmd
}