jenkins - How to pass variables from Jenkinsfile to shell command

Question

I want to use a variable which I am using inside of my Jenkinsfile script, and then pass its value into a shell script execution (either as an environment variable or command line parameter).

But the following Jenkinsfile:

for (i in [ 'a', 'b', 'c' ]) {
    echo i
    sh 'echo "from shell i=$i"'
}

Gives the output:

a
from shell i=
b
from shell i=
c
from shell i=

Desired output is something like:

a
from shell i=a
b
from shell i=b
c
from shell i=c

Any idea how to pass the value of i to the shell scipt?

Edit: Based upon Matt's answer, I now use this solution:

for (i in [ 'a', 'b', 'c' ]) {
    echo i
    sh "i=${i}; " + 'echo "from shell i=$i"'
}

The advantage is, that I don't need to escape the " in the shell script.

Answer 1

Your code is using a literal string and therefore your Jenkins variable will not be interpolated inside the shell command. You need to use " to interpolate your variable inside your strings inside the sh. ' will just pass a literal string. So we need to make a few changes here.

The first is to change the ' to ":

for (i in [ 'a', 'b', 'c' ]) {
  echo i
  sh "echo "from shell i=$i""
}

However, now we need to escape the " on the inside:

for (i in [ 'a', 'b', 'c' ]) {
  echo i
  sh "echo "from shell i=$i""
}

Additionally, if a variable is being appended directly to a string like you are doing above ($i onto i=), we need to close it off with some curly braces:

for (i in [ 'a', 'b', 'c' ]) {
  echo i
  sh "echo "from shell i=${i}""
}

That will get you the behavior you desire.