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

• 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 another example of using the =~ operator, see Example A-28.