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.

  #!/bin/bash for i in {1..10} # Simpler and more straightforward than #+ for i in $(seq 10) do echo -n "$i " done echo # 1 2 3 4 5 6 7 8 9 10

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

  #!/bin/bash Array=(element-zero element-one element-two element-three) echo ${Array[0]} # element-zero # First element of array. echo ${!Array[@]} # 0 1 2 3 # All the indices of Array. for i in ${!Array[@]} do echo ${Array[i]} # element-zero # element-one # element-two # element-three # # All the elements in Array. done

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

  #!/bin/bash variable="This is a fine mess." echo "$variable" if [[ "$variable" =~ "T*fin*es*" ]] # Regex matching with =~ operator within [[ double brackets ]]. then echo "match found" # match found fi

  Or, more usefully:

  #!/bin/bash input=$1 if [[ "$input" =~ "[1-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9][0-9][0-9]" ]] # NNN-NN-NNNN # Where each N is a digit. # But, initial digit must not be 0. then echo "Social Security number." # Process SSN. else echo "Not a Social Security number!" # Or, ask for corrected input. fi

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

The update to version 3 of Bash breaks a few scripts that worked under earlier versions. Test critical legacy scripts to make sure they still work! As it happens, a couple of the scripts in the Advanced Bash Scripting Guide had to be fixed up (see Example A-20 and Example 9-4, for instance).