RegEx for "does not begin with"

Question

The following checks if it begins with "End":

if [[ "$line" =~ ^End ]]

I am trying to find out how to match something that does not begin with "02/18/13". I have tried the following:

if [[ "$line" != ^02/18/13 ]]

if [[ "$line" != ^02\/18\/13 ]]

Neither of them seemed to work.

Answer 1

bash doesn't have a "doesn't match regex" operator; you can either negate (!) a test of the "does match regex" operator (=~):

if [[ ! "$line" =~ ^02/18/13 ]]

or use the "doesn't match string/glob pattern" operator (!=):

if [[ "$line" != 02/18/13* ]]

Glob patterns are just different enough from regular expressions to be confusing. In this case, the pattern is simple enough that the only difference is that globs are expected to match the entire string, and hence don't need to be anchored (in fact, it needs a wildcard to de-anchor the end of the pattern).

Answer 2

Why not just "if not" it?

if ! [[ "$line" =~ ^02/18/13 ]]

Answer 3

Using the if ! will do the trick. Example: Say line="1234" using this test in bash -

if ! echo "$line" |grep -q "^:" > /dev/null; then echo "GOOD line does NOT begin with : "; else echo "BAD - line DOES begin with : "; fi

It will respond with "GOOD line does NOT begin with : "