"If X exists" about script

[bitfield]

I'd love some suggestions for what this might look like!

[frioux]

Wouldn't it be something like:

func IsFile(path string) (bool, error) {
   s, err := os.Stat(path)
   if err != nil {
       if os.IsNotExist(err) {
          return false, nil
       }
       return false, err
   }

   return !s.IsDir(), nil
}

[bitfield]

Sorry—my fault for not being clear. Yes, the implementation would probably look something like what you quoted, though we need to think about whether we should consider both files and directories to 'exist'.

The more difficult question is about how it would work within script pipelines. For example, would it be something like:

script.IfExists("/srv/foo/config.txt").Exec("/usr/bin/configure-service")

What do you think? A use case would be helpful here. Have you ever written a script which has logic based on whether or not a file exists?

[frioux]

Here are some examples I have on hand (in shell:)

if [ -f $x ]; then
     cat $x
else
     ls $x --color
fi

if [ -f "$HOME/.goobook_auth.json" ]; then
   goobook query '' >> "$TMP"
   < $TMP grep -v '^ ' | sponge $TMP
fi

if [ -f "$HOME/.dbic.json" ]; then
   export DBIC_TRACE_PROFILE="$HOME/.dbic.json"
fi

if [[ ! -f ~/.dotfilecheck ]]; then
   echo $(($EPOCHSECONDS+60*60*24*7)) > ~/.dotfilecheck
fi

[bitfield]

Great! Would you mind writing out one of these examples using script, as you would like to see it?

[bitfield]

@frioux (or anyone else) do you have any comments on the proposed design?

[frioux]

I don't use script, this just seemed easy enough to implement that I didn't understand the outstanding issue.

…

-- Sent from a rotary phone rented from Ma Bell

[bitfield]

Well, then it's even more helpful of you to pop in and make suggestions! I appreciate it.

Here's the final result:

// IfExists tests whether the specified file exists, and returns a pipe whose
// error status reflects the result. If the file doesn't exist, the pipe's error
// status will be set, and if the file does exist, the pipe will have no error
// status.
func IfExists(filename string) *Pipe {
	_, err := os.Stat(filename)
	if err != nil {
		return NewPipe().WithError(err)
	}
	return NewPipe()
}