The following table identifies some Perl 5 regular expressions you can use. Similarly, the Examples using the Perl 5 regular expressions table  suggests specific examples based on this notation.

Table 1. Perl 5 regular expressions
Perl 5 expression Description
. Matches exactly one character, regardless of what the character is.
? The preceding item is optional and matched at most once (error if no preceding item).
* The preceding item will be matched zero or more times (error if no preceding item).
+ The preceding item will be matched one or more times (error if no preceding item).
^ Match at beginning of a line.
$ Match at end of a line.
{n} The preceding item is matched exactly n times (error if no preceding item).
{n, } The preceding item is matched n or more times (error if no preceding item).
{,m} The preceding item is optional and is matched at most m times (error if no preceding item).
{n,m} The preceding item is matched at least ntimes, but not more than m times (error if no preceding item).
[abc] Matches the characters a OR b OR c.
[a-z] Matches any character from a to z.
[^abc] Matches any character EXCEPT a, b, or c.
\d Matches exactly one digit.
\D Matches any character EXCEPT a digit.
\w Matches exactly one letter, number, or the underscore character(_).
\W Matches any one character EXCEPT a letter, number, or the underscore character.
\s Matches exactly one character of white space (for example, spaces, tabs, newlines, or any character that would not use ink if printed on a printer).
\S Matches any character that is NOT a white space.
\ Dereferences metacharacters (called "quoting").
| Separates two or more choices such as either|or behavior.

The following table provides some examples based on the Perl 5 regular expressions identified in the above table.

Table 2. Examples using the Perl 5 regular expressions
Example Description
^error Matches the exact word error only when it appears at the beginning of a line.
\(9239\)$ Matches the exact entry (9239) only when it appears at the end of a line.
da.*e Matches the exact words date, daze, database, and dattape. This Perl 5 regular expression, .*, is similar to the wild card * on UNIX.
abc|abd|abe Matches abc, abd, and abe.
b.d Matches bad, bud, and bid, but not bald.
da.....e Matches database and dattape, but not date and daze.
3.14 Matches 3.14, 3f14, and 3814.
3\.14 Matches 3.14, but not 3f14 and 3814.
ab?c Matches ac and abc.
ab*c Matches ac, abc, abbc, abbbc, and so forth.
ab+c Matches abc, abbc, and so forth, but not ac.
d\.*z Matches dz, d.z, d..z, d...z, and so forth.
d.\*z Matches da*z, db*z, dc*z, and so forth.
1\.\d\d Matches any three-digit floating point number from 1.00 to 1.99******.
a\Dc Matches abc, a&c, and aFc, but not a2c or a8c.
a\wc Matches abc, aGc, and a_c, but not a%c.
a\Wc Matches a%c, a?c, and a c, but not abc, aGc, or a_c.
a\sc Matches any three-character string starting with a and ending with c whose second character is a space, tab, or newline.
a\Sc Matches any three-character string starting with a and ending with c whose second character is not a space, tab, or newline.
ab{3,5}c Matches abbbc, abbbbc, abbbbbc, only.
.{3,5} pentane Matches cyclopentane, neopentane, and isopentane, but not n-pentane.
a[bc]d Matches abd and acd, only.
a[a-z]c Matches any three-character string starting with a and ending with c, and whose second character is any letter from a to z, inclusive.