sed command with dynamic variable and spaces - not retaining spaces - linux

Question

I am trying to insert a variable value into file from Jenkinsfile using shell script in the section
Variable value is dynamic. I am using sed.
Sed is working fine but it is not retaining the white spaces that the variable have at the beginning.
ex:
The value of >> repoName is " somename"
stage('trying sed command') {
steps {
script {
sh """
#!/bin/bash -xel
repo='${repoName}'
echo "\$repo"
`sed -i "5i \$repo" filename`
cat ecr.tf
"""
}
}
}
current output:
names [
"xyz",
"ABC",
somename
"text"
]
Expected output:
names [
"xyz",
"ABC",
somename
"text"
]
How do i retain the spaces infront of the variable passing from sed

Answer 1

With
$ cat filename
names [
"xyz",
"ABC",
"text"
]
$ repo=somename
we can do:
sed -E "3s/^([[:blank:]]*).*/&\\n\\1${repo},/" filename
names [
"xyz",
"ABC",
somename,
"text"
]
That uses capturing parentheses to grab the indentation from the previous line.
if $repo might contain a value with slashes, you can tell the shell to escape them with this (eye-opening) expansion
repo='some/name'
sed -E "3s/^([[:blank:]]*).*/&\\n\\1${repo//\//\\\/},/" filename
names [
"xyz",
"ABC",
some/name,
"text"
]

Answer 2

I used 1 sed statement to add the content first to the file and then another sed statement for just adding spaces. This fixed my issue. All day i was trying to fit in one command did not work probably from Jenkins and shell usage. But using 2 sed commands as a workaround i was able to finish my task

Answer 3

The i command skips over spaces after the i command to find the text to insert. You can put the text on a new line, with a backslash before the newline, to have the initial whitespace preserved.
stage('trying sed command') {
steps {
script {
sh """
#!/bin/bash -xel
repo='${repoName}'
echo "\$repo"
`sed -i "5i \\\\\\
\$repo" filename`
cat ecr.tf
"""
}
}
}
I've tested this from a regular shell command line, I hope it will also work in the Jenkins recipe.