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# 12. Regular expressions
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#### Overview
[Perl Compatible Regular
Expressions](https://en.wikipedia.org/wiki/Perl_Compatible_Regular_Expressions)
(PCRE) are supported in Zabbix.
There are two ways of using regular expressions in Zabbix:
- manually entering a regular expression
- using a global regular expression created in Zabbix
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#### Regular expressions
You may manually enter a regular expression in supported places. Note
that the expression may not start with @ because that symbol is used in
Zabbix for referencing global regular expressions.
::: notewarning
It's possible to run out of stack when using regular
expressions. See the [pcrestack man
page](http://pcre.org/original/doc/html/pcrestack.html) for more
information.
:::
Note that in multi-line matching, the `^` and `$` anchors match at the
beginning/end of each line respectively, instead of the beginning/end of
the entire string.
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#### Global regular expressions
There is an advanced editor for creating and testing complex regular
expressions in Zabbix frontend.
Once a regular expression has been created this way, it can be used in
several places in the frontend by referring to its name, prefixed with
@, for example, *\@mycustomregexp*.
To create a global regular expression:
- Go to: *Administration → General*
- Select *Regular expressions* from the dropdown
- Click on *New regular expression*
The **Expressions** tab allows to set the regular expression name and
add subexpressions.
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All mandatory input fields are marked with a red asterisk.
|Parameter|<|Description|
|---------|-|-----------|
|*Name*|<|Set the regular expression name. Any Unicode characters are allowed.|
|*Expressions*|<|Click on *Add* in the Expressions block to add a new subexpression.|
|<|*Expression type*|Select expression type:
**Character string included** - match the substring
**Any character string included** - match any substring from a delimited list. The delimited list includes a comma (,), a dot (.) or a forward slash (/).
**Character string not included** - match any string except the substring
**Result is TRUE** - match the regular expression
**Result is FALSE** - do not match the regular expression|
|^|*Expression*|Enter substring/regular expression.|
|*Delimiter*|<|A comma (,), a dot (.) or a forward slash (/) to separate text strings in a regular expression. This parameter is active only when "*Any character string included*" expression type is selected.|
|*Case sensitive*|<|A checkbox to specify whether a regular expression is sensitive to capitalization of letters.|
Since Zabbix 2.4.0, a forward slash (/) in the expression is treated
literally, rather than a delimiter. This way it is possible to save
expressions containing a slash, whereas previously it would produce an
error.
::: noteimportant
A custom regular expression name in Zabbix may
contain commas, spaces, etc. In those cases where that may lead to
misinterpretation when referencing (for example, a comma in the
parameter of an item key) the whole reference may be put in quotes like
this: *"\@My custom regexp for purpose1, purpose2"*.\
Regular expression names must not be quoted in other locations (for
example, in LLD rule properties).
:::
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#### Example
Use of the following regular expression in LLD to discover databases not
taking into consideration a database with a specific name:
^TESTDATABASE$
Chosen *Expression type*: "Result is FALSE". Doesn't match name,
containing string "*TESTDATABASE*".
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#### Example with an inline regex modifier
Use of the following regular expression including an inline modifier
(?i) to match the characters "error":
(?i)error
Chosen *Expression type*: "Result is TRUE". Characters "error" are
matched.
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#### Another example with an inline regex modifier
Use of the following regular expression including multiple inline
modifiers to match the characters after a specific line:
(?<=match (?i)everything(?-i) after this line\n)(?sx).*# we add s modifier to allow . match newline characters
Chosen Expression type: "Result is TRUE". Characters after a specific
line are matched.
::: noteimportant
**g** modifier can't be specified in line. The
list of available modifiers can be found in [pcresyntax man
page](https://www.pcre.org/original/doc/html/pcresyntax.html#SEC16). For
more information about PCRE syntax please refer to [PCRE HTML
documentation](https://www.pcre.org/original/doc/html/pcrepattern.html).
:::
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#### More complex example
A custom regular expression may consist of multiple subexpressions, and
it can be tested in the **Test** tab by providing a test string.
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Results show the status of each subexpression and total custom
expression status.
Total custom expression status is defined as *Combined result*. If
several sub expressions are defined Zabbix uses AND logical operator to
calculate *Combined result*. It means that if at least one Result is
False *Combined result* has also False status.
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#### Explanation of global regular expressions
|Global regexp|Expression|Description|
|-------------|----------|-----------|
|*File systems for discovery*|`^(btrfs\|ext2\|ext3\|ext4\|jfs\|reiser\|xfs\|ffs\|ufs\|jfs\|jfs2\|vxfs\|hfs\|refs\|apfs\|ntfs\|fat32\|zfs)$`|Matches "btrfs" or "ext2" or "ext3" or "ext4" or "jfs" or "reiser" or " xfs" or "ffs" or "ufs" or "jfs" or "jfs2" or "vxfs" or "hfs" or "refs" or "apfs" or "ntfs" or "fat32" or "zfs"|
|*Network interfaces for discovery*|`^Software Loopback Interface`|Matches strings starting with "Software Loopback Interface"|
|<|`^lo$`|Matches "lo"|
|<|`^(In)?[Ll]oop[Bb]ack[0-9._]*$`|Matches strings that optionally start with "In", then have "L" or "l", then "oop", then "B" or "b", then "ack", which can be optionally followed by any number of digits, dots or underscores|
|<|`^NULL[0-9.]*$`|Matches strings staring with "NULL" optionally followed by any number of digits or dots|
|<|`^[Ll]o[0-9.]*$`|Matches strings starting with "Lo" or "lo" and optionally followed by any number of digits or dots|
|<|`^[Ss]ystem$`|Matches "System" or "system"|
|<|`^Nu[0-9.]*$`|Matches strings staring with "Nu" optionally followed by any number of digits or dots|
|*Storage devices for SNMP discovery*|`^(Physical memory\|Virtual memory\|Memory buffers\|Cached memory\|Swap space)$`|Matches "Physical memory" or "Virtual memory" or "Memory buffers" or "Cached memory" or "Swap space"|
|*Windows service names for discovery*|`^(MMCSS\|gupdate\|SysmonLog\|clr_optimization_v2.0.50727_32\|clr_optimization_v4.0.30319_32)$`|Matches "MMCSS" or "gupdate" or "SysmonLog" or strings like "clr\_optimization\_v2.0.50727\_32" and "clr\_optimization\_v4.0.30319\_32" where instead of dots you can put any character except newline.|
|*Windows service startup states for discovery*|`^(automatic\|automatic delayed)$`|Matches "automatic" or "automatic delayed".|
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#### Regular expression support by location
|Location|<|Regular expression|Global regular expression|Comments|
|--------|-|------------------|-------------------------|--------|
|**[Agent items](/manual/config/items/itemtypes/zabbix_agent)**|<|<|<|<|
|<|eventlog\[\]|Yes|Yes|`regexp`, `severity`, `source`, `eventid` parameters|
|^|log\[\]|^|^|`regexp` parameter|
|^|log.count\[\]|^|^|^|
|^|logrt\[\]|^|Yes/No|`regexp` parameter supports both, `file_regexp` parameter supports non-global expressions only|
|^|logrt.count\[\]|^|^|^|
|^|proc.cpu.util\[\]|^|No|`cmdline` parameter|
|^|proc.mem\[\]|^|^|^|
|^|proc.num\[\]|^|^|^|
|^|sensor\[\]|^|^|`device` and `sensor` parameters on Linux 2.4|
|^|system.hw.macaddr\[\]|^|^|`interface` parameter|
|^|system.sw.packages\[\]|^|^|`package` parameter|
|^|vfs.dir.count\[\]|^|^|`regex_incl`, `regex_excl` parameters, since 4.0.4 also `regex_excl_dir` parameter|
|^|vfs.dir.size\[\]|^|^|`regex_incl`, `regex_excl` parameters, since 4.0.4 also `regex_excl_dir` parameter|
|^|vfs.file.regexp\[\]|^|^|`regexp` parameter|
|^|vfs.file.regmatch\[\]|^|^|^|
|^|web.page.regexp\[\]|^|^|^|
|**[SNMP traps](/manual/config/items/itemtypes/snmptrap)**|<|<|<|<|
|<|snmptrap\[\]|Yes|Yes|`regexp` parameter|
|**[Item value preprocessing](/manual/config/items/item#item_value_preprocessing)**|<|Yes|No|`pattern` parameter|
|**[Trigger functions](/manual/appendix/triggers/functions)**|<|<|<|<|
|<|count()|Yes|Yes|`pattern` parameter if `operator` parameter is *regexp* or *iregexp*|
|^|logeventid()|^|^|`pattern` parameter|
|^|logsource()|^|^|^|
|^|iregexp()|^|^|^|
|^|regexp()|^|^|^|
|**[Low-level discovery](/manual/discovery/low_level_discovery#discovery_rule_filter)**|<|Yes|Yes|*Filter* field|
|**[Web monitoring](/manual/web_monitoring#configuring_a_web_scenario)**|<|Yes|No|*Variables* with a **regex:** prefix
*Required string* field|
|**[Macro functions](/manual/config/macros/macro_functions)**|<|<|<|<|
|<|regsub()|Yes|No|`pattern` parameter|
|^|iregsub()|^|^|^|
|**[Icon mapping](/manual/web_interface/frontend_sections/administration/general#icon_mapping)**|<|Yes|Yes|*Expression* field|
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