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Brace expansion

Multiple expansions are featured in Bash. One of the most basic yet powerful is brace expansion.

Basic usage

Words containing a brace expansion are expanded into a list of words where the brace expansion was replaced with each of the comma separated elements within the brace expansion.

In this specific case, I will not try to explain more this feature which is pretty hard to explain but easy to understand from examples. So let us start!

List of strings

• mv file_{new,old} is equivalent to mv file_new file_old
• cp file{,_backup}_data is equivalent to cp file_data file_backup_data
• mkdir md_{C2H2,C2H4,H2O,CO}_Pt111_CP2K is equivalent to mkdir md_C2H2_Pt111_CP2K md_C2H4_Pt111_CP2K md_H2O_Pt111_CP2K md_CO_Pt111_CP2K

Beware that brace expansion is not performed in a quoted string: touch file_{a,e} "data_{a,e}" is equivalent to touch file_a file_e "data_{a,e}".

Beware also about unescaped spaces in your words touch file {a,e} "file "{a,e} is equivalent to touch file a e file_a file_e.

Ranges

• mkdir dir{3..5} is equivalent to mkdir dir3 dir4 dir5
• mkdir cutoff_{100..200..50} is equivalent to mkdir cutoff_100 cutoff_150 cutoff_200
• mkdir test{b..f} is equivalent to mkdir testb testc testd teste testf

Advanced usage

Multiple brace expansions can be applied to a same word: mkdir md_{CO,H2O}_{top,fcc} is equivalent to mkdir md_CO_top md_CO_fcc md_H2O_top md_H2O_fcc.

Brace expansions can be nested: mkdir dir{a,b,{1..3}} is equivalent to mkdir dira dirb dir1 dir2 dir3.

Parameters expansion are compatible with brace expansion: touch {$HOME,~rstaub,$(pwd)}/data is equivalent to touch /home/rstaub/data ~rstaub/data ./data.