---
name: "hadd"
section: "1"
platform: "linux"
package: "root"
version: "6.40.04-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/hadd"
---

# hadd(1)

## SYNOPSIS

usage: hadd \[-a\] \[-f\] \[-f\[0-9\]\] \[-fk\] \[-ff\] \[-k\] \[-L\] \[-Ltype\] \[-O\] \[-T\]\
             \[-v V\] \[-j J\] \[-dbg\] \[-d D\] \[-n N\] \[-cachesize CACHESIZE\]\
             \[-experimental-io-features EXPERIMENTAL\_IO\_FEATURES\]\
             TARGET SOURCES

## DESCRIPTION

This program will add histograms, trees and other objects from a list of ROOT files and write them to a target ROOT file. The target file is newly created and must not exist, or if -f ("force") is given, must not be one of the source files.

## OPTIONS

- \-a

  Append to the output

- \-f

  Force overwriting of output file

- \-f\[0-9\]

  Gives the ability to specify the compression algorithm i and level j

-

  of the target file, by passing the number i\*100 + j, e.g. -f505. The

-

  last digit (j) can be set from 0 = uncompressed to 9 = highly

-

  compressed. The first digit (i) is 1 for ZLIB, 2 for LZMA, 4 for LZ4

-

  and 5 for ZSTD. Recommended numbers are 101 (ZLIB), 207 (LZMA), 404

-

  (LZ4), 505 (ZSTD). The default value for this flag is 101

-

  (kDefaultZLIB). See ROOT::RCompressionSetting and TFile::TFile

-

  documentation for more details.

- \-fk

  Sets the target file to contain the baskets with the same compression

-

  as the input files (unless -O is specified). Compresses the meta data

-

  using the compression level specified in the first input or the

-

  compression setting after fk (for example 206 when using -fk206)

- \-ff

  The compression level use is the one specified in the first input

- \-k

  Skip corrupt or non-existent files, do not exit

- \-L

  Read the list of objects from FILE and either only merge or skip those

-

  objects depending on the value of "-Ltype". FILE must contain one

-

  object name per line, which cannot contain whitespaces or '/'. You can

-

  also pass TDirectory names, which apply to the entire directory

-

  content. Lines beginning with '#' are ignored. If this flag is passed,

-

  "-Ltype" MUST be passed as well.

- \-Ltype

  Sets the type of operation performed on the objects listed in FILE

-

  given with the "-L" flag. "SkipListed" will skip all the listed

-

  objects; "OnlyListed" will only merge those objects. If this flag is

-

  passed, "-L" must be passed as well.

- \-O

  Re-optimize basket size when merging TTree

- \-T

  Do not merge Trees

- \-v

  Explicitly set the verbosity level: 0 request no output, 99 is the

-

  default

- \-j

  Parallelize the execution in 'J' processes. If the number of processes

-

  is not specified, use the system maximum.

- \-dbg

  Enable verbosity. If -j was specified, do not not delete partial files

-

  stored inside working directory.

- \-d

  Carry out the partial multiprocess execution in the specified

-

  directory

- \-n

  Open at most 'N' files at once (use 0 to request to use the system

-

  maximum)

- \-cachesize

  Resize the prefetching cache use to speed up I/O operations (use 0 to

-

  disable)

- \-experimental-io-features

  Used with an argument provided, enables the corresponding experimental

-

  feature for output trees. See ROOT::Experimental::EIOFeatures

- TARGET

  Target file

- SOURCES

  Source files