Using regular expressions with match and sub in AWK

In AWK, regular expressions can be used with the `match` and `sub` functions to manipulate and transform strings.

The `match` function is used to search a string for a regular expression pattern, and returns the position of the match and the length of the matched substring. The basic syntax of `match` is:

match(string, regexp)

Here is an example of using `match` to search a string for a pattern:

str = "apple banana cherry"
if (match(str, /banana/) > 0) {
  print "Found banana"
}

In this example, we use `match` to search the string `str` for the pattern “banana”. If the pattern is found, `match` returns the position of the match (in this case, 7) and the length of the matched substring (in this case, 6).

The `sub` function is used to substitute a regular expression pattern in a string with a replacement string. The basic syntax of `sub` is:

sub(regexp, replacement, target)

Here is an example of using `sub` to replace a pattern in a string:

str = "apple banana cherry"
sub(/banana/, "orange", str)
print str

In this example, we use `sub` to replace the pattern “banana” in the string `str` with the string “orange”. The `sub` function modifies the`target` string in place, so after the function call, `str` contains the new value “apple orange cherry”.

You can also use regular expression capture groups in the replacement string to include parts of the matched string in the replacement. Capture groups are indicated by parentheses in the regular expression pattern, and are referred to as `\1`, `\2`, `\3`, etc. in the replacement string. Here is an example:

str = "John Smith"
sub(/(\w+) (\w+)/, "\2, \1", str)
print str

In this example, we use `sub` to swap the first and last names in the string “John Smith”. The regular expression pattern `(\w+) (\w+)` matches two words separated by a space, and captures them as two groups. The replacement string `”\2, \1″` includes the second group followed by a comma, and then the first group. After the function call, `str` contains the new value “Smith, John”.

Regular expressions can also be used in patterns and actions in AWK to match and process input data. Refer to the previous answer for examples of using patterns and actions in AWK.