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Answer 1

+1 A:

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

Teddy 2010-01-07 07:23:33

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.

Jonathan Leffler 2010-01-18 08:29:24

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

Teddy 2010-01-18 08:38:24

Answer 2

A:

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

ghostdog74 2010-01-07 07:44:34

Answer 3

+1 A:

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

Dennis Williamson 2010-01-07 08:32:10

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adding or changing variable value

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