## Removing version information in IDs

Identifiers (IDs) in public databases often contain version information. For example, .16 in ENSG00000100644.16 from Ensembl and .1 in NM_001243084.1 from RefSeq. Such version information can be an obstacle to join entries from different databases. So, version information should be trimmed before joining. The file that contains such IDs with version information id.txt can be converted by tiny Perl script like

% perl -i~ -pe 's/([^\.]+)\./\$1/g' id.txt


Original file will be renamed to id.txt~, and converted file is now named as id.txt.