sed or awk with variable and special charachters - awk

Question

I want to use awk or sed to substitute 1 line in my file:
my file content is:
server.modules += ( "mod_redirect" )
$SERVER["socket"] == ":8080" {
$HTTP["host"] =~ "(.*)" {
url.redirect = ( "^/(.*)" => "https://someurl.com/unauthorised" )
}
}
I want to change the line containing url.redirect
The new line is in variable and containing some special charachter will be somthing like this url.redirect = ( "^/(.*)" => "http://newurl.com/newpath" )
so I used the following sed comand:
sed "/url\.redirect =/s/.*/$newline/" 10-redirect.conf
But I got error related to the special characters inside the newline variable.
the newline is an argument of my shell function so I can not change it and add some skip characters inside.
How to use variables with special charachters in sed or awk?

Answer 1

With GNU sed and c command (which replaces the matched lines with the string provided). If there are spaces at the start of string, prefix \ to preserve them
sed '/url\.redirect =/c\'"$newline"
However, c command will still allow escape sequences, for example:
$ s=' rat\tdog\nwolf'
$ seq 3 | sed '2c\'"$s"
1
rat dog
wolf
3
To add contents literally and robustly, use r command
echo "$newline" | sed -e '/url\.redirect =/ {r /dev/stdin' -e 'd}'
Here's r command in action
$ s=' rat\tdog\nwolf'
$ echo "$s" | sed -e '2 {r /dev/stdin' -e 'd}' <(seq 3)
1
rat\tdog\nwolf
3

Answer 2

Could you please try following. This should put same spaces in front of new value what were present before.
newline='url.redirect = ( "^/(.*)" => "https://example.com/authorised" )'
awk -v line="$newline" '
/url.redirect =/{
match($0,/^ +/)
print substr($0,RSTART,RLENGTH) line
next
}
1
' Input_file

Answer 3

You are getting error in sed because it is using a regex and your replacement string may contain meta-characters such as & or / (delimiters) etc.
This awk would be safer to use due to non-regex approach:
newline='url.redirect = ( "^/(.*)" => "https://example.com/authorised" )'
awk -i inplace -v line="$newline" 'index($0, "url.redirect =") {
sub(/[^[:blank:]].*/, "")
$0 = $0 line
} 1' file
server.modules += ( "mod_redirect" )
$SERVER["socket"] == ":8080" {
$HTTP["host"] =~ "(.*)" {
url.redirect = ( "^/(.*)" => "https://example.com/authorised" )
}
}
Note that using ENVIRON would allow all the shell special characters to
awk:
export newline
awk -i inplace 'index($0, "url.redirect =") {
sub(/[^[:blank:]].*/, "")
$0 = $0 ENVIRON["newline"]
} 1' file