Validating Input
Problem
You’ve asked for input (e.g., from a user or a program) and to ensure security or data integrity you need to make sure you got what you asked for.
Solution
There are various ways to validate your input, depending on what the input is and how strict you need to be.
Use pattern matching for simple “it matches or it doesn’t” situations (see Testing for Equal, Testing with Pattern Matches, and Testing with Regular Expressions).
[[ "$raw_input" == *.jpg ]] && echo "Got a JPEG file."
Use a case statement when there are various things that might be valid (see Branching Many Ways and Parsing Command-Line Arguments).
# cookbook filename: validate_using_case case $raw_input in *.company.com ) # Probably a local hostname ;; *.jpg ) # Probably a JPEG file ;; *.[jJ][pP][gG] ) # Probably a JPEG file, case insensitive ;; foo | bar ) # entered 'foo' or 'bar ;; [0-9][0-9][0-9] ) # A 3 digit number ;; [a-z][a-z][a-z][a-z] ) # A 4 lower-case char word ;; * ) # None of the above ;; esac
Use a regular expression when pattern matching isn’t specific
enough and you have bash version 3.0+ (see Testing with Regular Expressions). This example is looking
for a three to six alphanumeric character filename with a .jpg
extension (case sensitive):
[[ "$raw_input" =~ [[:alpha:]]{3,6}\.jpg ]] && echo "Got a JPEG file."
Discussion
For a larger and more detailed example, see the examples/scripts/shprompt in a recent bash tarball. Note this was written by Chet Ramey, who maintains bash:
# shprompt -- ...
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