How to use custom variables in gitlab ci/cd?

Question

I'm struggling with gitlab ci/cd variables. I see so many conflicting examples. Anyhow, what I would like to know is how to use variables outside and within scripts.

For example, in a job config, can I assign a variable in the script section with a bash command?

some-job:
   variables:
      SOME_VAR: ''
   script:
      - SOME_VAR = $(<file_with_a_line_of_text.txt)

In the above case, I'm not sure if I can do this. But I need to populate a variable with the file contents (i.e. artifact). Also, when do I use '$' in front of the variable? Some examples I see using these formats:

"SOME_VAR" #in quotes, no dollar sign
"${SOME_VAR}" #in quotes, with dollar sign and wrapped with curly braces
${SOME_VAR} #no quotes, with dollar sign and wrapped with curly braces
$SOME_VAR #i.e. without the double quotes or curly braces
SOME_VAR #i.e. without the double quotes, dollar sign, and curly braces

So many variations of usage that I can see in examples but don't really know when to use each style. And I can't find one example online of a custom variable being set in a script using a bash command.

Answer 1

When I'm setting variables in bash, I always do it without the spaces around the =:

VAR1="some string"
VAR2=23
VAR3=true
VAR4=$(cat /path/to/file.txt)

Let's go through these examples one at a time:

1. You can set a variable as a string by using quotes around the string.
2. You can set it to an int (probably a float too, but haven't personally used it)
3. You can set it to a bool
4. You can set it to the output of a command. The command is inside the command: $(#command).

Now let's use them:

echo $VAR1
# some string
echo "This is my variable $VAR1"
# This is my variable some string
echo "This is my variable ${VAR1}"
# This is my variable some string
echo ${VAR1}
# some string
echo "Error code ${VAR2}A"
# Error code 23A
echo "Error code $VAR2A"
# Error code --- Note: the variable $VAR2A dosn't exist
echo "Error code ${VAR2}${VAR1}"
# Error code 23some string
echo VAR1
# VAR1
echo "VAR1"
# VAR1

This illustrates the difference between the different forms, but in general, you reference a variable's value with $+variable-name. Doing "SOME_VAR" or SOME_VAR just prints out the string "SOME_VAR" (ie, not referencing a variable at all).

The difference between $SOME_VAR and ${SOME_VAR} is that the latter lets you use it when there is other content directly before or after the variable without erroring.

Answer 2

How to use custom variables in gitlab ci/cd?

Normally like in any other shell.

But note that gitlab-ci.yml is a yaml file and yaml has special parsings. Because of that in script: ex. - echo bla is the same as - 'echo bla', because in yaml the content of script: is an array of strings that are later spitted by shell.

how to use variables outside and within scripts.

Normally like in any other shell script.

when to use each style

"SOME_VAR" #in quotes, no dollar sign
SOME_VAR #i.e. without the double quotes, dollar sign, and curly braces

when you want to have a string SOME_VAR literally

"${SOME_VAR}"

is the same as "$SOME_VAR". When you want to have the content of SOME_VAR variable literally.

${SOME_VAR} #no quotes, with dollar sign and wrapped with curly braces
$SOME_VAR #i.e. without the double quotes or curly braces

When you want the content of SOME_VAR variable after word splitting and filename expansion. That means that SOME_VAR='*' and then echo "$SOME_VAR" will print *, but echo $SOME_VAR will print all files in current directory. You usually always want to quote expansions.

The form ${SOME_VAR} is used if concatenated with some other string, ex. $SOME_VARbla is not ${SOME_VAR}bla.

Do not use upper case variables in your scripts - prefer lower case. Prefer using upper case variables for exported variables. Be aware of clashes - COLUMN PATH USER UID are examples of already used variables.

can I assign a variable in the script section with a bash command?

Shell is space aware. var = val will execute a command named var with two arguments = and val. var=val will assign the string val to variable named var. Do:

- SOME_VAR=$(<file_with_a_line_of_text.txt)

In gitlab-ci I would prefer to use cat in case I will want to move to alpine. $(< is a bash extension.

- SOME_VAR=$(cat file_with_a_line_of_text.txt)

There doesn't seem to be any point in setting providing SOME_VAR in environment with variables: SOME_VAR.

When do I use '$' in front of the variable?

When you want to trigger variable expansion. Variable expansion substitutes variable name for the variable value.

Check your scripts with http://shellcheck.net . Read https://mywiki.wooledge.org/BashGuide a good shell introduction and https://wiki.bash-hackers.org/scripting/obsolete .