---
name: "srf_index_hash"
section: "1"
platform: "linux"
package: "staden-io-lib-utils"
version: "1.15.0-1.1+b2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/srf_index_hash"
---

# srf\_index\_hash(1)

Adds a hash-table index to an SRF file.

## NAME

**srf\_index\_hash** - Adds a hash-table index to an SRF file.

## SYNOPSIS

**srf\_index\_hash**  \[*-c\] srf\_archive*

## DESCRIPTION

**srf\_index\_hash** adds and index to an SRF file or replaces an existing index with a new one. In the case of concatenated SRF files only the index at the end of a file will be replaced, but internal indices will not be consulted by SRF tools.

The index is a hash table indexing the sequence names only. The name itself does not appear in the index, rather the top 7-bits of a 64-bit hash key are held in the index along with N-bits used to determine the hash bucket. This reduces the index size to around 10-15 bytes per sequence.

## OPTIONS

- **-c**

  Check only. This requests that the index is not produced, but the checks performed during the creation of an index (such as looking for duplicate sequence names) are still performed.

## AUTHOR

James Bonfield, Wellcome Trust Sanger Institute