Shell Tricks: convert file urls to UNIX paths

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Today’s shell trick is for converting file:// urls into valid shell paths. This isn’t a terribly common scenario, but I occasionally work with tools, especially in GUI applications, that output file urls and need to change something like:

file:///Users/ttscoff/Desktop/my%20file.txt

into:

~/Desktop/my\ file.txt 

These are Bash-specific, due mostly to some variable mangling syntax, but could easily be converted for zsh and others.

I’ve broken functions for unescaping percent-encoded input, shell escaping regular text, and trimming full paths to tilde abbreviations (when needed) into separate utility functions because they’re reusable and useful in other functions and aliases.

I handle shell escaping with the default Ruby Shellwords module. It’s fast and covers edge cases, avoiding a lot of sed/awk work. There are modules in other scripting languages as well, but Ruby and the Shellwords module are standard on all OS X systems (and what I know best). Substitute based on your personal preference.

# Ruby ShellWords escape
shellesc() {
    local output
    # If any arguments are passed to the function, assume that's the input
    if [[ $# == 0 ]]; then
        output=$(ruby -e 'require "shellwords"; puts Shellwords.escape(STDIN.read.strip)')
    # otherwise, take input from STDIN so it can be used in piped commands
    else
        output=$(ruby -e 'require "shellwords"; puts Shellwords.escape(ARGV.join(" ").strip)' $@)
    fi

    echo "$output"
}

I also use Ruby (CGI class methods) to unescape urls when working in the shell. It will convert any percent-encoded entities to their natural state:

# Ruby cgi unescape
unesc() {
    local output

    if [[ $# == 0 ]]; then
        output=$(ruby -r cgi -e 'require "cgi"; puts CGI.unescape(STDIN.read)')
    else
        output=$(ruby -e 'require "cgi"; puts CGI.unescape(ARGV.join(" "))' $@)
    fi
    
    echo "$output"
}

Lastly, a quick utility using sed to replace full paths in home directory with a tilde (~), e.g. /Users/ttscoff/Desktop becomes ~/Desktop. It’s more readable and allows more portability as the tilde will expand to whatever the current user’s home folder is.

Note: When input is recieved from STDIN instead of arguments, it automatically calls the shell escape function to avoid losing existing escaping through the read command. Thus a call to shellesc | shorthome in other functions is redundant (though not fatal).

shorthome() {
    local input
    if [[ $# == 0 ]]; then
        read input
        input=$(shellesc "$input")
    else
        input="$@"
    fi
    echo -n "$input" | sed -E "s/^${HOME//\//\\/}/~/"
}

Lastly, here’s the function that combines the previous utility functions to convert a file:// url to a shell-escaped path.

If you pass -c as the first argument (or only argument if you want to use piped input from STDIN), results are copied to the clipboard (using pbcopy, which is OS X-only). The bulk of the function is a simple piped chain of the above functions, with a quick variable mangling in Bash to remove the file:// prefix.

# convert a file:// URL to shell path
url2path() {
    local input output
    local copy=false
    if [[ $1 == '-c' ]]; then
        copy=true
        shift
    fi
    if [[ $# == 0 ]]; then
        read input
    else
        input=$@
    fi

    # 1. Replace 'file://', `%20` (space), and other entities in the url
    # 2. Add shell escaping for spaces and any non-legal characters
    # 3. Replace hardcoded home paths with the tilde abbreviation
    output=$(unesc ${input#file:\/\/} | shorthome)

    if $copy; then
        echo -n "$output"|pbcopy
        echo "Result in clipboard"
    else
        echo -n "$output"
    fi
}

With that code sourced in your ~/.bash_profile, you can use commands such as echo "file:///Users/ttscoff/Desktop/my%20file.md" | url2path or url2path file:///Users/ttscoff/Desktop/my%20file.md to get the filepath, either directly or as part of another script.

The command (usable as an alias) pbpaste | url2path -c will convert a url in the clipboard into a file path, in place, ready for pasting.

Ryan Irelan has produced a series of shell trick videos based on BrettTerpstra.com posts. Readers can get 10% off using the coupon code TERPSTRA.