Bash Brace Expansion

(this post if part of the material I cover in my devops course)

About Brace Expansions

This post is based on the documentation of bash brace expansion.

• Brace expansion is a mechanism that creates strings
• The basic syntax is:
  • optional preanble (an opening string)
    • a series of comma-separated strings or
    • a sequence expression between a pair of braces
  • optional postscript (a closing string)
• The preamble is prefixed to each string contained within the braces
• The postscript is then appended to each resulting string, expanding left to right.
• Here's a basic example:

 1$> 
 2$> printf "%s\n" A{1,2,3,4}B
 3A1B
 4A2B
 5A3B
 6A4B
 7$> 
 8$> for word in A{1,2,3,4}B
 9> do
10> printf "%s\n" $word
11> done
12A1B
13A2B
14A3B
15A4B
16$> 

Sequence Brace Expansion

• A sequence expression takes the form {x..y[..incr]}, where:
  • x and y are either integers or letters
  • incr, an optional increment, is an integer.
• Example:

 1$> printf "%s\n" A{0..30..3}B
 2A0B
 3A3B
 4A6B
 5A9B
 6A12B
 7A15B
 8A18B
 9A21B
10A24B
11A27B
12A30B
13$> 

• example with letters:

1$> printf "%s\n" +{a..z..4}-
2+a-
3+e-
4+i-
5+m-
6+q-
7+u-
8+y-
9$> 

Nested Brace Expansions

Just an example:

 1$> printf "%s\n" +{{A..E},f,g,{H..K}}+
 2+A+
 3+B+
 4+C+
 5+D+
 6+E+
 7+f+
 8+g+
 9+H+
10+I+
11+J+
12+K+
13$>