Plain text matching

Equality

Use single or double equals sign - the same in newer shells.

[[ VARIABLE == VALUE ]]

e.g.

[[ "$NAME" == "Joe" ]]

Starts with

Test using == and a pattern with a * globstar and no quotes.

# macOS
OSTYPE=darwin19.0

[[ "$OSTYPE" == darwin* ]] && echo 'Yes' || echo 'No'
# Yes

Contains

A more specific case of pattern matching. Use = or ==.

[[ VALUE == *NEEDLE* ]]

e.g.

MSG="I like dogs, don't you?"
[[ MSG == *dog* ]] && echo 'Yes' || echo 'No'
Yes

Note lack of quotes so that * gets expanded for the check. In this case * does not have to do with paths like it usually does.

GREETING='Hello, world'

[[ "$GREETING" = *lo* ]] && echo 'Match' || echo 'No match'
Match

Check if a string is in your OS type.

[[ "$OSTYPE" = *darwin* ]] && echo 'I'm a mac' || echo 'I'm not a mac'

Regex pattern matching

Use =~ and a regex pattern.

[[ STRING =~ PATTERN ]]

Be sure to not use quotes on the pattern or you’ll get unexpected behavior.

Basic

No special functionality. Just string contains.

[[ "$PATH" =~ ruby ]] && echo 'Yes' || echo 'No'

Starts with

FIRST=abc
SECOND=def

[[ "$FIRST" =~ '^d' ]] && echo 'Match' || echo 'No match'
# No match
[[ "$SECOND" =~ '^d' ]] && echo 'Match' || echo 'No match'
# Match

[[ "main" =~ ^m ]] && echo 'Yes' || echo 'No'
# Yes

[[ "$PATH" =~ ^/ ]] && echo 'Yes' || echo 'No'

List

FRUIT='apple'
[[ "$FRUIT" =~ banana|apple|orange ]] && echo 'Yes' || echo 'No'
# Yes

Negate:

if [[ ! "$FRUIT" =~ banana|apple|orange ]]; then
  echo 'Your fruit is not one of the allowed fruit'
  exit 1
fi

Pattern as a variable

Store your regex pattern as a variable and then use it later.

PATTERN='banana|apple|orange'

FRUIT='apple'
[[ "$FRUIT" =~ "$PATTERN" ]] && echo 'Yes' || echo 'No'
# Yes