adding or changing variable value

Question

I want to add the following line to /etc/my.cnf

server-id=1789051

The line may or may not be there. If it is there, it is usually server-id=1 If my IP is 192.178.90.51 then the server id should be 1789051

I want to know if a shell script or a command can do it.

Dennis Williamson · Accepted Answer · 2010-01-07 08:32:10Z

1

This will replace the line in the same position in the file, if it exists, rather than moving it to the end. If it doesn't exist, it will append it to the end of the file.

sed  '1{x;s/^$/server-id=1789051/;x};/^server-id=/{s/^.*$//;x};${G;s/\n//}' /etc/my.cnf

answered Jan 7, 2010 at 8:32

Dennis Williamson

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Teddy · Accepted Answer · 2010-01-07 07:23:33Z

1

sed --in-place --expression='$aserver-id=1789051' --expression='/^server-id=/d' \
    /etc/my.cnf

answered Jan 7, 2010 at 7:23

Teddy

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2 Comments

Jonathan Leffler Over a year ago

The '--in-place' works with GNU sed - not with POSIX standard versions of sed. The notation used with '$a' (to append at the end) is also unique to GNU sed; the standard versions require a backslash and a newline in the script. That said, it seems to work with GNU sed.

Teddy Over a year ago

@Jonathan Leffler: I would have thought that the double-dash long options was a clear enough indicator that this is, indeed, GNU sed.

ghostdog74 · Accepted Answer · 2010-01-07 07:44:34Z

0

one way with awk

#!/bin/bash
ip=1.2.3.4
awk -v ip="$ip" '/server-id/{
    $0="server-id="ip;f=0
    f=1
    g=1
}
{print}
END{
  if(g==0){ print "server-id="ip  }
}' file

output when there is "server-id"

$ more file
1
2
server-id=1
end
$ ./shell.sh
1
2
server-id=1.2.3.4
end

output when there is no "server-id"

$ more file
1
2
end
$ ./shell.sh
1
2
end
server-id=1.2.3.4

answered Jan 7, 2010 at 7:44

ghostdog74

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