34.2. Bash, version 3

On July 27, 2004, Chet Ramey released version 3 of Bash. This update fixes quite a number of bug in Bash and adds some new features.

Some of the added features are:

• A new, more generalized {a..z} brace expansion operator.

  1 #!/bin/bash 2  3 for i in {1..10} 4 # Simpler and more straightforward than 5 #+ for i in $(seq 10) 6 do 7  echo -n "$i " 8 done 9  10 echo 11  12 # 1 2 3 4 5 6 7 8 9 10 13  14  15  16 # Or just . . . 17  18 echo {a..z} # a b c d e f g h i j k l m n o p q r s t u v w x y z 19 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 20  # Works backwards, too. 21 echo {3..-2} # 3 2 1 0 -1 -2 22 echo {X..d} # X Y Z [ ] _ ` a b c d 23  # Shows (some of) the ASCII characters between Z and a, 24  #+ but don't rely on this type of behavior because . . . 25 echo {]..a} # {]..a} 26  # Why?

• The ${!array[@]} operator, which expands to all the indices of a given array.

  1 #!/bin/bash 2  3 Array=(element-zero element-one element-two element-three) 4  5 echo ${Array[0]} # element-zero 6  # First element of array. 7  8 echo ${!Array[@]} # 0 1 2 3 9  # All the indices of Array. 10  11 for i in ${!Array[@]} 12 do 13  echo ${Array[i]} # element-zero 14  # element-one 15  # element-two 16  # element-three 17  # 18  # All the elements in Array. 19 done

• The =~ Regular Expression matching operator within a double brackets test expression. (Perl has a similar operator.)

  1 #!/bin/bash 2  3 variable="This is a fine mess." 4  5 echo "$variable" 6  7 if [[ "$variable" =~ "T*fin*es*" ]] 8 # Regex matching with =~ operator within [[ double brackets ]]. 9 then 10  echo "match found" 11  # match found 12 fi

  Or, more usefully:

  1 #!/bin/bash 2  3 input=$1 4  5  6 if [[ "$input" =~ "[1-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9][0-9][0-9]" ]] 7 # NNN-NN-NNNN 8 # Where each N is a digit. 9 # But, initial digit must not be 0. 10 then 11  echo "Social Security number." 12  # Process SSN. 13 else 14  echo "Not a Social Security number!" 15  # Or, ask for corrected input. 16 fi

  For additional examples of using the =~ operator, see Example A-30, Example 18-14, Example A-36, and Example A-25.

• The new set -o pipefail option is useful for debugging pipes. If this option is set, then the exit status of a pipe is the exit status of the last command in the pipe to fail (return a non-zero value), rather than the actual final command in the pipe.

  See Example 15-40.