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Brace Expansion

Perhaps the strangest expansion is called brace expansion. With it, you can create multi- ple text strings from a pattern containing braces. Here's an example:

[me@linuxbox ~]$ echo Front-{A,B,C}-Back

Front-A-Back Front-B-Back Front-C-Back

[me@linuxbox ~]$ echo Front-{A,B,C}-Back

Front-A-Back Front-B-Back Front-C-Back

Patterns to be brace expanded may contain a leading portion called a preamble and a trailing portion called a postscript. The brace expression itself may contain either a comma-separated list of strings, or a range of integers or single characters. The pattern may not contain embedded whitespace. Here is an example using a range of integers:

[me@linuxbox ~]$ echo Number_{1..5}

Number_1 Number_2 Number_3 Number_4 Number_5

[me@linuxbox ~]$ echo Number_{1..5}

Number_1 Number_2 Number_3 Number_4 Number_5

Integers may also be zero-padded like so:

[me@linuxbox ~]$ echo {01..15}

01 02 03 04 05 06 07 08 09 10 11 12 13 14 15

[me@linuxbox ~]$ echo {01..15}

01 02 03 04 05 06 07 08 09 10 11 12 13 14 15

[me@linuxbox ~]$ echo {001..15}

001 002 003 004 005 006 007 008 009 010 011 012 013 014 015

[me@linuxbox ~]$ echo {001..15}

001 002 003 004 005 006 007 008 009 010 011 012 013 014 015

A range of letters in reverse order:

[me@linuxbox ~]$ echo {Z..A}

Z Y X W V U T S R Q P O N M L K J I H G F E D C B A

[me@linuxbox ~]$ echo {Z..A}

Z Y X W V U T S R Q P O N M L K J I H G F E D C B A

Brace expansions may be nested:

[me@linuxbox ~]$ echo a{A{1,2},B{3,4}}b

aA1b aA2b aB3b aB4b

[me@linuxbox ~]$ echo a{A{1,2},B{3,4}}b

aA1b aA2b aB3b aB4b

So what is this good for? The most common application is to make lists of files or direc- tories to be created. For example, if we were photographers and had a large collection of images that we wanted to organize into years and months, the first thing we might do is create a series of directories named in numeric “Year-Month” format. This way, the direc- tory names will sort in chronological order. We could type out a complete list of directo- ries, but that's a lot of work and it's error-prone too. Instead, we could do this:

[me@linuxbox ~]$ mkdir Photos

[me@linuxbox ~]$ cd Photos

[me@linuxbox Photos]$ mkdir {2007..2009}-{01..12}

[me@linuxbox Photos]$ ls

Pretty slick!

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