debian-mirror-gitlab/doc/ci/variables

GitLab CI/CD Variables

When receiving a job from GitLab CI, the Runner prepares the build environment. It starts by setting a list of predefined variables (environment variables) and a list of user-defined variables.

Priority of variables

The variables can be overwritten and they take precedence over each other in this order:

1. Trigger variables or scheduled pipeline variables (take precedence over all)
2. Project-level variables or protected variables
3. Group-level variables or protected variables
4. YAML-defined job-level variables
5. YAML-defined global variables
6. Deployment variables
7. Predefined variables (are the lowest in the chain)

For example, if you define API_TOKEN=secure as a project variable and API_TOKEN=yaml in your .gitlab-ci.yml, the API_TOKEN will take the value secure as the project variables are higher in the chain.

Unsupported variables

There are cases where some variables cannot be used in the context of a .gitlab-ci.yml definition (for example under script). Read more about which variables are not supported.

Predefined variables (Environment variables)

Some of the predefined environment variables are available only if a minimum version of GitLab Runner is used. Consult the table below to find the version of Runner required.

NOTE: Note: Starting with GitLab 9.0, we have deprecated some variables. Read the 9.0 Renaming section to find out their replacements. You are strongly advised to use the new variables as we will remove the old ones in future GitLab releases.

Variable	GitLab	Runner	Description
ARTIFACT_DOWNLOAD_ATTEMPTS	8.15	1.9	Number of attempts to download artifacts running a job
CI	all	0.4	Mark that job is executed in CI environment
CI_COMMIT_REF_NAME	9.0	all	The branch or tag name for which project is built
CI_COMMIT_REF_SLUG	9.0	all	$CI_COMMIT_REF_NAME lowercased, shortened to 63 bytes, and with everything except 0-9 and a-z replaced with -. No leading / trailing -. Use in URLs, host names and domain names.
CI_COMMIT_SHA	9.0	all	The commit revision for which project is built
CI_COMMIT_BEFORE_SHA	11.2	all	The previous latest commit present on a branch before a push request.
CI_COMMIT_TAG	9.0	0.5	The commit tag name. Present only when building tags.
CI_COMMIT_MESSAGE	10.8	all	The full commit message.
CI_COMMIT_TITLE	10.8	all	The title of the commit - the full first line of the message
CI_COMMIT_DESCRIPTION	10.8	all	The description of the commit: the message without first line, if the title is shorter than 100 characters; full message in other case.
CI_CONFIG_PATH	9.4	0.5	The path to CI config file. Defaults to .gitlab-ci.yml
CI_DEBUG_TRACE	all	1.7	Whether debug tracing is enabled
CI_DEPLOY_USER	10.8	all	Authentication username of the GitLab Deploy Token, only present if the Project has one related.
CI_DEPLOY_PASSWORD	10.8	all	Authentication password of the GitLab Deploy Token, only present if the Project has one related.
CI_DISPOSABLE_ENVIRONMENT	all	10.1	Marks that the job is executed in a disposable environment (something that is created only for this job and disposed of/destroyed after the execution - all executors except shell and ssh). If the environment is disposable, it is set to true, otherwise it is not defined at all.
CI_ENVIRONMENT_NAME	8.15	all	The name of the environment for this job
CI_ENVIRONMENT_SLUG	8.15	all	A simplified version of the environment name, suitable for inclusion in DNS, URLs, Kubernetes labels, etc.
CI_ENVIRONMENT_URL	9.3	all	The URL of the environment for this job
CI_JOB_ID	9.0	all	The unique id of the current job that GitLab CI uses internally
CI_JOB_MANUAL	8.12	all	The flag to indicate that job was manually started
CI_JOB_NAME	9.0	0.5	The name of the job as defined in .gitlab-ci.yml
CI_JOB_STAGE	9.0	0.5	The name of the stage as defined in .gitlab-ci.yml
CI_JOB_TOKEN	9.0	1.2	Token used for authenticating with the GitLab Container Registry and downloading dependent repositories
CI_JOB_URL	11.1	0.5	Job details URL
CI_REPOSITORY_URL	9.0	all	The URL to clone the Git repository
CI_RUNNER_DESCRIPTION	8.10	0.5	The description of the runner as saved in GitLab
CI_RUNNER_ID	8.10	0.5	The unique id of runner being used
CI_RUNNER_TAGS	8.10	0.5	The defined runner tags
CI_RUNNER_VERSION	all	10.6	GitLab Runner version that is executing the current job
CI_RUNNER_REVISION	all	10.6	GitLab Runner revision that is executing the current job
CI_RUNNER_EXECUTABLE_ARCH	all	10.6	The OS/architecture of the GitLab Runner executable (note that this is not necessarily the same as the environment of the executor)
CI_PIPELINE_ID	8.10	0.5	The unique id of the current pipeline that GitLab CI uses internally
CI_PIPELINE_IID	11.0	all	The unique id of the current pipeline scoped to project
CI_PIPELINE_TRIGGERED	all	all	The flag to indicate that job was triggered
CI_PIPELINE_SOURCE	10.0	all	Indicates how the pipeline was triggered. Possible options are: push, web, trigger, schedule, api, and pipeline. For pipelines created before GitLab 9.5, this will show as unknown
CI_PROJECT_DIR	all	all	The full path where the repository is cloned and where the job is run
CI_PROJECT_ID	all	all	The unique id of the current project that GitLab CI uses internally
CI_PROJECT_NAME	8.10	0.5	The project name that is currently being built (actually it is project folder name)
CI_PROJECT_NAMESPACE	8.10	0.5	The project namespace (username or groupname) that is currently being built
CI_PROJECT_PATH	8.10	0.5	The namespace with project name
CI_PROJECT_PATH_SLUG	9.3	all	$CI_PROJECT_PATH lowercased and with everything except 0-9 and a-z replaced with -. Use in URLs and domain names.
CI_PIPELINE_URL	11.1	0.5	Pipeline details URL
CI_PROJECT_URL	8.10	0.5	The HTTP address to access project
CI_PROJECT_VISIBILITY	10.3	all	The project visibility (internal, private, public)
CI_REGISTRY	8.10	0.5	If the Container Registry is enabled it returns the address of GitLab's Container Registry
CI_REGISTRY_IMAGE	8.10	0.5	If the Container Registry is enabled for the project it returns the address of the registry tied to the specific project
CI_REGISTRY_PASSWORD	9.0	all	The password to use to push containers to the GitLab Container Registry
CI_REGISTRY_USER	9.0	all	The username to use to push containers to the GitLab Container Registry
CI_SERVER	all	all	Mark that job is executed in CI environment
CI_SERVER_NAME	all	all	The name of CI server that is used to coordinate jobs
CI_SERVER_REVISION	all	all	GitLab revision that is used to schedule jobs
CI_SERVER_VERSION	all	all	GitLab version that is used to schedule jobs
CI_SHARED_ENVIRONMENT	all	10.1	Marks that the job is executed in a shared environment (something that is persisted across CI invocations like shell or ssh executor). If the environment is shared, it is set to true, otherwise it is not defined at all.
GET_SOURCES_ATTEMPTS	8.15	1.9	Number of attempts to fetch sources running a job
GITLAB_CI	all	all	Mark that job is executed in GitLab CI environment
GITLAB_USER_EMAIL	8.12	all	The email of the user who started the job
GITLAB_USER_ID	8.12	all	The id of the user who started the job
GITLAB_USER_LOGIN	10.0	all	The login username of the user who started the job
GITLAB_USER_NAME	10.0	all	The real name of the user who started the job
RESTORE_CACHE_ATTEMPTS	8.15	1.9	Number of attempts to restore the cache running a job

9.0 Renaming

To follow conventions of naming across GitLab, and to further move away from the build term and toward job CI variables have been renamed for the 9.0 release.

NOTE: Note: Starting with GitLab 9.0, we have deprecated the $CI_BUILD_* variables. You are strongly advised to use the new variables as we will remove the old ones in future GitLab releases.

8.x name	9.0+ name
CI_BUILD_ID	CI_JOB_ID
CI_BUILD_REF	CI_COMMIT_SHA
CI_BUILD_TAG	CI_COMMIT_TAG
CI_BUILD_BEFORE_SHA	CI_COMMIT_BEFORE_SHA
CI_BUILD_REF_NAME	CI_COMMIT_REF_NAME
CI_BUILD_REF_SLUG	CI_COMMIT_REF_SLUG
CI_BUILD_NAME	CI_JOB_NAME
CI_BUILD_STAGE	CI_JOB_STAGE
CI_BUILD_REPO	CI_REPOSITORY_URL
CI_BUILD_TRIGGERED	CI_PIPELINE_TRIGGERED
CI_BUILD_MANUAL	CI_JOB_MANUAL
CI_BUILD_TOKEN	CI_JOB_TOKEN

.gitlab-ci.yml defined variables

NOTE Note: This feature requires GitLab Runner 0.5.0 or higher and GitLab CI 7.14 or higher.

GitLab CI allows you to add to .gitlab-ci.yml variables that are set in the build environment. The variables are hence saved in the repository, and they are meant to store non-sensitive project configuration, e.g., RAILS_ENV or DATABASE_URL.

For example, if you set the variable below globally (not inside a job), it will be used in all executed commands and scripts:

variables:
  DATABASE_URL: "postgres://postgres@postgres/my_database"

The YAML-defined variables are also set to all created service containers, thus allowing to fine tune them.

Variables can be defined at a global level, but also at a job level. To turn off global defined variables in your job, define an empty hash:

job_name:
  variables: {}

You are able to use other variables inside your variable definition (or escape them with $$):

variables:
  LS_CMD: 'ls $FLAGS $$TMP_DIR'
  FLAGS: '-al'
script:
  - 'eval $LS_CMD'  # will execute 'ls -al $TMP_DIR'

Variables

NOTE: Note: Group-level variables were added in GitLab 9.4.

CAUTION: Important: Be aware that variables are not masked, and their values can be shown in the job logs if explicitly asked to do so. If your project is public or internal, you can set the pipelines private from your project's Pipelines settings. Follow the discussion in issue #13784 for masking the variables.

GitLab CI allows you to define per-project or per-group variables that are set in the pipeline environment. The variables are stored out of the repository (not in .gitlab-ci.yml) and are securely passed to GitLab Runner making them available during a pipeline run. It's the recommended method to use for storing things like passwords, SSH keys and credentials.

Project-level variables can be added by going to your project's Settings > CI/CD, then finding the section called Variables.

Likewise, group-level variables can be added by going to your group's Settings > CI/CD, then finding the section called Variables. Any variables of subgroups will be inherited recursively.

Once you set them, they will be available for all subsequent pipelines. You can also protect your variables.

Protected variables

Notes: This feature requires GitLab 9.3 or higher.

Variables could be protected. Whenever a variable is protected, it would only be securely passed to pipelines running on the protected branches or protected tags. The other pipelines would not get any protected variables.

Protected variables can be added by going to your project's Settings > CI/CD, then finding the section called Variables, and check "Protected".

Once you set them, they will be available for all subsequent pipelines.

Manually-specified variables

Introduced in GitLab 10.8.

Variables can be specified for a single pipeline run when a manual pipeline is created.

Deployment variables

NOTE: Note: This feature requires GitLab CI 8.15 or higher.

Project services that are responsible for deployment configuration may define their own variables that are set in the build environment. These variables are only defined for deployment jobs. Please consult the documentation of the project services that you are using to learn which variables they define.

An example project service that defines deployment variables is the Kubernetes integration.

Debug tracing

Introduced in GitLab Runner 1.7.

CAUTION: Warning: Enabling debug tracing can have severe security implications. The output will contain the content of all your variables and any other secrets! The output will be uploaded to the GitLab server and made visible in job traces!

By default, GitLab Runner hides most of the details of what it is doing when processing a job. This behavior keeps job traces short, and prevents secrets from being leaked into the trace unless your script writes them to the screen.

If a job isn't working as expected, this can make the problem difficult to investigate; in these cases, you can enable debug tracing in .gitlab-ci.yml. Available on GitLab Runner v1.7+, this feature enables the shell's execution trace, resulting in a verbose job trace listing all commands that were run, variables that were set, etc.

Before enabling this, you should ensure jobs are visible to team members only. You should also erase all generated job traces before making them visible again.

To enable debug traces, set the CI_DEBUG_TRACE variable to true:

job_name:
  variables:
    CI_DEBUG_TRACE: "true"

Example truncated output with debug trace set to true:

...

export CI_SERVER_TLS_CA_FILE="/builds/gitlab-examples/ci-debug-trace.tmp/CI_SERVER_TLS_CA_FILE"
if [[ -d "/builds/gitlab-examples/ci-debug-trace/.git" ]]; then
  echo $'\''\x1b[32;1mFetching changes...\x1b[0;m'\''
  $'\''cd'\'' "/builds/gitlab-examples/ci-debug-trace"
  $'\''git'\'' "config" "fetch.recurseSubmodules" "false"
  $'\''rm'\'' "-f" ".git/index.lock"
  $'\''git'\'' "clean" "-ffdx"
  $'\''git'\'' "reset" "--hard"
  $'\''git'\'' "remote" "set-url" "origin" "https://gitlab-ci-token:xxxxxxxxxxxxxxxxxxxx@example.com/gitlab-examples/ci-debug-trace.git"
  $'\''git'\'' "fetch" "origin" "--prune" "+refs/heads/*:refs/remotes/origin/*" "+refs/tags/*:refs/tags/*"
else
  $'\''mkdir'\'' "-p" "/builds/gitlab-examples/ci-debug-trace.tmp/git-template"
  $'\''rm'\'' "-r" "-f" "/builds/gitlab-examples/ci-debug-trace"
  $'\''git'\'' "config" "-f" "/builds/gitlab-examples/ci-debug-trace.tmp/git-template/config" "fetch.recurseSubmodules" "false"
  echo $'\''\x1b[32;1mCloning repository...\x1b[0;m'\''
  $'\''git'\'' "clone" "--no-checkout" "https://gitlab-ci-token:xxxxxxxxxxxxxxxxxxxx@example.com/gitlab-examples/ci-debug-trace.git" "/builds/gitlab-examples/ci-debug-trace" "--template" "/builds/gitlab-examples/ci-debug-trace.tmp/git-template"
  $'\''cd'\'' "/builds/gitlab-examples/ci-debug-trace"
fi
echo $'\''\x1b[32;1mChecking out dd648b2e as master...\x1b[0;m'\''
$'\''git'\'' "checkout" "-f" "-q" "dd648b2e48ce6518303b0bb580b2ee32fadaf045"
'
+++ hostname
++ echo 'Running on runner-8a2f473d-project-1796893-concurrent-0 via runner-8a2f473d-machine-1480971377-317a7d0f-digital-ocean-4gb...'
Running on runner-8a2f473d-project-1796893-concurrent-0 via runner-8a2f473d-machine-1480971377-317a7d0f-digital-ocean-4gb...
++ export CI=true
++ CI=true
++ export CI_DEBUG_TRACE=false
++ CI_DEBUG_TRACE=false
++ export CI_COMMIT_SHA=dd648b2e48ce6518303b0bb580b2ee32fadaf045
++ CI_COMMIT_SHA=dd648b2e48ce6518303b0bb580b2ee32fadaf045
++ export CI_COMMIT_BEFORE_SHA=dd648b2e48ce6518303b0bb580b2ee32fadaf045
++ CI_COMMIT_BEFORE_SHA=dd648b2e48ce6518303b0bb580b2ee32fadaf045
++ export CI_COMMIT_REF_NAME=master
++ CI_COMMIT_REF_NAME=master
++ export CI_JOB_ID=7046507
++ CI_JOB_ID=7046507
++ export CI_REPOSITORY_URL=https://gitlab-ci-token:xxxxxxxxxxxxxxxxxxxx@example.com/gitlab-examples/ci-debug-trace.git
++ CI_REPOSITORY_URL=https://gitlab-ci-token:xxxxxxxxxxxxxxxxxxxx@example.com/gitlab-examples/ci-debug-trace.git
++ export CI_JOB_TOKEN=xxxxxxxxxxxxxxxxxxxx
++ CI_JOB_TOKEN=xxxxxxxxxxxxxxxxxxxx
++ export CI_PROJECT_ID=1796893
++ CI_PROJECT_ID=1796893
++ export CI_PROJECT_DIR=/builds/gitlab-examples/ci-debug-trace
++ CI_PROJECT_DIR=/builds/gitlab-examples/ci-debug-trace
++ export CI_SERVER=yes
++ CI_SERVER=yes
++ export 'CI_SERVER_NAME=GitLab CI'
++ CI_SERVER_NAME='GitLab CI'
++ export CI_SERVER_VERSION=
++ CI_SERVER_VERSION=
++ export CI_SERVER_REVISION=
++ CI_SERVER_REVISION=
++ export GITLAB_CI=true
++ GITLAB_CI=true
++ export CI=true
++ CI=true
++ export GITLAB_CI=true
++ GITLAB_CI=true
++ export CI_JOB_ID=7046507
++ CI_JOB_ID=7046507
++ export CI_JOB_TOKEN=xxxxxxxxxxxxxxxxxxxx
++ CI_JOB_TOKEN=xxxxxxxxxxxxxxxxxxxx
++ export CI_COMMIT_REF=dd648b2e48ce6518303b0bb580b2ee32fadaf045
++ CI_COMMIT_REF=dd648b2e48ce6518303b0bb580b2ee32fadaf045
++ export CI_COMMIT_BEFORE_SHA=dd648b2e48ce6518303b0bb580b2ee32fadaf045
++ CI_COMMIT_BEFORE_SHA=dd648b2e48ce6518303b0bb580b2ee32fadaf045
++ export CI_COMMIT_REF_NAME=master
++ CI_COMMIT_REF_NAME=master
++ export CI_COMMIT_NAME=debug_trace
++ CI_JOB_NAME=debug_trace
++ export CI_JOB_STAGE=test
++ CI_JOB_STAGE=test
++ export CI_SERVER_NAME=GitLab
++ CI_SERVER_NAME=GitLab
++ export CI_SERVER_VERSION=8.14.3-ee
++ CI_SERVER_VERSION=8.14.3-ee
++ export CI_SERVER_REVISION=82823
++ CI_SERVER_REVISION=82823
++ export CI_PROJECT_ID=17893
++ CI_PROJECT_ID=17893
++ export CI_PROJECT_NAME=ci-debug-trace
++ CI_PROJECT_NAME=ci-debug-trace
++ export CI_PROJECT_PATH=gitlab-examples/ci-debug-trace
++ CI_PROJECT_PATH=gitlab-examples/ci-debug-trace
++ export CI_PROJECT_NAMESPACE=gitlab-examples
++ CI_PROJECT_NAMESPACE=gitlab-examples
++ export CI_PROJECT_URL=https://example.com/gitlab-examples/ci-debug-trace
++ CI_PROJECT_URL=https://example.com/gitlab-examples/ci-debug-trace
++ export CI_PIPELINE_ID=52666
++ CI_PIPELINE_ID=52666
++ export CI_PIPELINE_IID=123
++ CI_PIPELINE_IID=123
++ export CI_RUNNER_ID=1337
++ CI_RUNNER_ID=1337
++ export CI_RUNNER_DESCRIPTION=shared-runners-manager-1.example.com
++ CI_RUNNER_DESCRIPTION=shared-runners-manager-1.example.com
++ export 'CI_RUNNER_TAGS=shared, docker, linux, ruby, mysql, postgres, mongo'
++ CI_RUNNER_TAGS='shared, docker, linux, ruby, mysql, postgres, mongo'
++ export CI_REGISTRY=registry.example.com
++ CI_REGISTRY=registry.example.com
++ export CI_DEBUG_TRACE=true
++ CI_DEBUG_TRACE=true
++ export GITLAB_USER_ID=42
++ GITLAB_USER_ID=42
++ export GITLAB_USER_EMAIL=user@example.com
++ GITLAB_USER_EMAIL=user@example.com
++ export VERY_SECURE_VARIABLE=imaverysecurevariable
++ VERY_SECURE_VARIABLE=imaverysecurevariable
++ mkdir -p /builds/gitlab-examples/ci-debug-trace.tmp
++ echo -n '-----BEGIN CERTIFICATE-----
MIIFQzCCBCugAwIBAgIRAL/ElDjuf15xwja1ZnCocWAwDQYJKoZIhvcNAQELBQAw'

...

Using the CI variables in your job scripts

All variables are set as environment variables in the build environment, and they are accessible with normal methods that are used to access such variables. In most cases bash or sh is used to execute the job script.

To access environment variables, use the syntax for your Runner's shell.

Shell	Usage
bash/sh	$variable
windows batch	%variable%
PowerShell	$env:variable

To access environment variables in bash, prefix the variable name with ($):

job_name:
  script:
    - echo $CI_JOB_ID

To access environment variables in Windows Batch, surround the variable with (%):

job_name:
  script:
    - echo %CI_JOB_ID%

To access environment variables in a Windows PowerShell environment, prefix the variable name with ($env:):

job_name:
  script:
    - echo $env:CI_JOB_ID

You can also list all environment variables with the export command, but be aware that this will also expose the values of all the variables you set, in the job log:

job_name:
  script:
    - export

Example values:

export CI_JOB_ID="50"
export CI_COMMIT_SHA="1ecfd275763eff1d6b4844ea3168962458c9f27a"
export CI_COMMIT_REF_NAME="master"
export CI_REPOSITORY_URL="https://gitlab-ci-token:abcde-1234ABCD5678ef@example.com/gitlab-org/gitlab-ce.git"
export CI_COMMIT_TAG="1.0.0"
export CI_JOB_NAME="spec:other"
export CI_JOB_STAGE="test"
export CI_JOB_MANUAL="true"
export CI_JOB_TRIGGERED="true"
export CI_JOB_TOKEN="abcde-1234ABCD5678ef"
export CI_PIPELINE_ID="1000"
export CI_PIPELINE_IID="10"
export CI_PROJECT_ID="34"
export CI_PROJECT_DIR="/builds/gitlab-org/gitlab-ce"
export CI_PROJECT_NAME="gitlab-ce"
export CI_PROJECT_NAMESPACE="gitlab-org"
export CI_PROJECT_PATH="gitlab-org/gitlab-ce"
export CI_PROJECT_URL="https://example.com/gitlab-org/gitlab-ce"
export CI_REGISTRY="registry.example.com"
export CI_REGISTRY_IMAGE="registry.example.com/gitlab-org/gitlab-ce"
export CI_RUNNER_ID="10"
export CI_RUNNER_DESCRIPTION="my runner"
export CI_RUNNER_TAGS="docker, linux"
export CI_SERVER="yes"
export CI_SERVER_NAME="GitLab"
export CI_SERVER_REVISION="70606bf"
export CI_SERVER_VERSION="8.9.0"
export GITLAB_USER_ID="42"
export GITLAB_USER_EMAIL="user@example.com"
export CI_REGISTRY_USER="gitlab-ci-token"
export CI_REGISTRY_PASSWORD="longalfanumstring"

Variables expressions

Variables expressions were added in GitLab 10.7.

It is possible to use variables expressions with only / except policies in .gitlab-ci.yml. By using this approach you can limit what jobs are going to be created within a pipeline after pushing a code to GitLab.

This is particularly useful in combination with variables and triggered pipeline variables.

deploy:
  script: cap staging deploy
  environment: staging
  only:
    variables:
      - $RELEASE == "staging"
      - $STAGING

Each expression provided is going to be evaluated before creating a pipeline.

If any of the conditions in variables evaluates to truth when using only, a new job is going to be created. If any of the expressions evaluates to truth when except is being used, a job is not going to be created.

This follows usual rules for only / except policies.

Supported syntax

Below you can find supported syntax reference:

1. Equality matching using a string

   Example: $VARIABLE == "some value"

   You can use equality operator == to compare a variable content to a string. We support both, double quotes and single quotes to define a string value, so both $VARIABLE == "some value" and $VARIABLE == 'some value' are supported. "some value" == $VARIABLE is correct too.

2. Checking for an undefined value

   Example: $VARIABLE == null

   It sometimes happens that you want to check whether a variable is defined or not. To do that, you can compare a variable to null keyword, like $VARIABLE == null. This expression is going to evaluate to truth if variable is not defined.

3. Checking for an empty variable

   Example: $VARIABLE == ""

   If you want to check whether a variable is defined, but is empty, you can simply compare it against an empty string, like $VAR == ''.

4. Comparing two variables

   Example: $VARIABLE_1 == $VARIABLE_2

   It is possible to compare two variables. This is going to compare values of these variables.

5. Variable presence check

   Example: $STAGING

   If you only want to create a job when there is some variable present, which means that it is defined and non-empty, you can simply use variable name as an expression, like $STAGING. If $STAGING variable is defined, and is non empty, expression will evaluate to truth. $STAGING value needs to a string, with length higher than zero. Variable that contains only whitespace characters is not an empty variable.

6. Pattern matching (added in 11.0)

   Example: $VARIABLE =~ /^content.*/

   It is possible perform pattern matching against a variable and regular expression. Expression like this evaluates to truth if matches are found.

   Pattern matching is case-sensitive by default. Use i flag modifier, like /pattern/i to make a pattern case-insensitive.