Regular Expressions

Regular expressions are patterns used to match character combinations in strings. In MaSH we can use regular expressions to perform text search and text replace operations. See here for more information on search and replace.

Contents

Creating a regular expression

To compose a regular expression in MaSH we provide an unquoted string surrounded by two forward slashes. The final slash can be followed by optional modifiers.

Natural

mash

set regex to /pattern/im

Standard

mash

regex = /pattern/im

Patterns

Brackets are used to find a range of characters:

Expression	Description
[abc]	Find one character from the options between the brackets
[^abc]	Find any character NOT between the brackets
[0-9]	Find one character from the range 0 to 9

Modifiers

Modifiers can change how a search is performed.

Modifier	Description
i	Performs a case-insensitive search
m	Performs a multiline search (patterns that search for the beginning or end of a string will match the beginning or end of each line)

Metacharacters

Metacharacters are characters with a special meaning:

Metacharacter	Description
\|	Find a match for any one of the patterns separated by \| as in: cat\|dog\|fish
.	Find just one instance of any character
^	Finds a match as the beginning of a string as in: ^Hello
$	Finds a match at the end of the string as in: World$
\d	Find a digit
\s	Find a whitespace character
\b	Find a match at the beginning of a word like this: \bWORD, or at the end of a word like this: WORD\b
\uxxxx	Find the Unicode character specified by the hexadecimal number xxxx

Quantifiers

Quantifiers define quantities:

Quantifier	Description
n+	Matches any string that contains at least one n
n*	Matches any string that contains zero or more occurrences of n
n?	Matches any string that contains zero or one occurrences of n
n{x}	Matches any string that contains a sequence of X n’s
n{x,y}	Matches any string that contains a sequence of X to Y n’s
n{x,}	Matches any string that contains a sequence of at least X n’s

If your expression needs to search for one of the special characters you can use a backslash ( \ ) to escape them. For example, to search for one or more question marks you can use the following expression pattern = /\?+/

Quantifiers don’t just apply to characters, you can also use them with metacharacters. For example, to search for two consecutive digits you can use the following expression pattern = /\d{2}/

`matches` – Using regular expressions with conditionals

We can use the matches operator inside conditionals in our mashlets to execute code if a regular expression is a match.

Natural

mash

set str to "How Now Brown Cow"

if str matches /^How/
  printline "Match"
end

if str matches /[Nn]ow/
  printline "Match"
end

if str matches /[A-Z]ow/
  printline "Match"
end

if str matches /[A-Za-z_0-9]ow/
  printline "Match"
end

Standard

mash

str = "How Now Brown Cow"

if (str matches /^How/) {
  printline("Match")
}

if (str matches /[Nn]ow/) {
  printline("Match")
}

if (str matches /[A-Z]ow/) {
  printline("Match")
}

if (str matches /[A-Za-z_0-9]ow/) {
  printline("Match")
}

Output

output

Match
Match
Match
Match

Grouping

You can use parentheses ( ) to apply quantifiers to entire patterns. They also can be used to select parts of the pattern to be used as a match.

Natural

mash

# Use grouping to search for the word "banana" by looking for ba followed by two instances of na:

set str to "Apples and bananas."
set pattern to /ba(na){2}/i

printline (str matches pattern)

Standard

mash

# Use grouping to search for the word "banana" by looking for ba followed by two instances of na:

str = "Apples and bananas."
pattern = /ba(na){2}/i

printline((str matches pattern))

Output

output

true

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