Get the directory of a TFile - Copy a root file from a directory to another directory

ROOT Version: 6.18/04
Platform: Ubuntu 18.04
Compiler: gcc 7.5.0 (Ubuntu 7.5.0-3)

Dear co-rooters,

I’m trying to open a root file and add a TBranch to it. Since I want to keep the original file, I thought of copying it and open the clone with the UPDATE option.

I tried copying the file by piping in bash and using cp command. If the file lives in another directory (i.e. I execute the macro by add_branch("../raw_data/run1.root") I get the following error

cp: cannot create regular file 'new_../raw_data/run1.root': No such file or directory
SysError in <TFile::TFile>: file new_../raw_data/run1.root can not be opened (No such file or directory)

I understand why I get this error and I know that if I add a suffix in the new file name instead of a prefix it will work. A snippet of my code is

void add_branch(TString filename_in){

    // (a) Open the file
    TFile *f_root = TFile::Open(filename_in, "READ");
    // copy the file with cp command
    TString new_filename_in = TString::Format("new_%s", filename_in.Data());
    gSystem->Exec( TString::Format("cp %s new_%s", filename_in.Data(), filename_in.Data()) );
    f_root = TFile::Open(new_filename_in, "UPDATE");


I also tried using the TFile::Cp() function but if the file lives in another directory things get complicated again because I get an error for the similar reasons.

[TFile::Cp] Total 1292.43 MB	|====================| 100.00 % [1104.8 MB/s]
SysError in <TFile::TFile>: file new_files/../raw_data/run1.root can not be opened (Not a directory)

This is a snippet of the code I’m using.

void add_branch(TString filename_in){

    // (a) Open the file
    TFile *f_root = TFile::Open(filename_in, "READ");

    //create a directory because Cp() wants it
    gSystem->Exec("mkdir new_files");
    // copy the file in a directory using Cp() function
    f_root = TFile::Open(TString::Format("new_files/%s", filename_in.Data()), "UPDATE");

What I need is to get the directory of the root file I’m opening but when I’m calling gDirectory->pwd() I also get the filename i.e.


Is there a way to get only the directory of the root file or does anyone have any idea on to copy the file?

Hi @atha.stam,
It’s easier for you to just cp the root file over to the new folder directly from your command line and then proceed with the modifications.

gDirectory->pwd() returns the path to the current TDirectory object, which does not correspond to the file system’s folder you are currently working in.

Have you tried to give it also the file name as in "new_files/run1.root" ?

Copying from the command line is an option but since this is supposed to be a macro to be used by people that want just to run a macro, I thought to make it as simple as possible.

I indeed tried to use Cp(new_file/filename.root")` but I got the same issue.

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