#!/bin/bash

variable="This is a fine mess."

echo "$variable"

# Regex matching with =~ operator within [[ double brackets ]].

if [[ "$variable" =~ T.........fin*es* ]]

# NOTE: 从bash V3.2开始，正则表达式不再用引号引起来
then
  echo "match found"

      # match found

fi

#!/bin/bash

input=$

if [[ "$input" =~ "[0-9][0-9][0-9]-[0-9][0-9]-[0-9][0-9][0-9][0-9]" ]]

#                 ^ NOTE: Quoting not necessary, as of version 3.2 of Bash.

# NNN-NN-NNNN (where each N is a digit).

then

  echo "Social Security number."

  # Process SSN.

else

  echo "Not a Social Security number!"

  # Or, ask for corrected input.

fi