sed -i empty argument compatibility issue

[Gary Aitken]

On 3/5/21 9:39 PM, Kyle Evans wrote:
> On Fri, Mar 5, 2021 at 3:03 PM Gary Aitken <freebsd at dreamchaser.org> wrote:
>>
>> I'm trying to come up with a fix for a script in a port which invokes sed.
>> The port comes from a linux environment, and the offending line looks like this:
>> (This is in a cMake file.)
>>
>> COMMAND sed -i "/^# /d" "${outfile}"
>>
>> The issue is that linux sed expects the -I or -i extension modifier to
>> immediately follow the -i.  In the above line, the extension is deliberately
>> missing to provide in-place editing.
>>
>> fbsd expects the extension to be separated from the -i by whitespace, or
>> doesn't work properly when it is empty or immediately follows the -i:
>>
>> $ !ls
>> ls -lt temp.tmp*
>> -rw-------  1 garya  garya  86 Mar  5 13:15 temp.tmp
>> -rw-------  1 garya  garya  86 Mar  5 13:15 temp.tmp_org
>> $ sed -ifoo "/^# /d" temp.tmp  (works on both fbsd & linux))
>> $ !ls
>> ls -lt temp.tmp*
>> -rw-------  1 garya  garya  30 Mar  5 13:48 temp.tmp
>> -rw-------  1 garya  garya  86 Mar  5 13:15 temp.tmp_org
>> -rw-------  1 garya  garya  86 Mar  5 13:15 temp.tmpfoo
>> $ cp -p temp.tmp_org temp.tmp
>> $ sed -i"" "/^# /d" temp.tmp   (works on linux but not fbsd)
>> sed: 1: "temp.tmp": undefined label 'emp.tmp'
>> $ sed -i "" "/^# /d" temp.tmp  (works on fbsd but not linux)
>> $ !ls
>> ls -lt temp.tmp*
>> -rw-------  1 garya  garya  30 Mar  5 13:49 temp.tmp
>> -rw-------  1 garya  garya  86 Mar  5 13:15 temp.tmp_org
>> -rw-------  1 garya  garya  86 Mar  5 13:15 temp.tmpfoo
>>
>> So fbsd works with '-i ""' but linux requires '-i""'
>>
>> Does anyone know a work-around for this problem?
>>
> 
> My personal favorite trick to bridge the gap here was, as I recall:
> 
> sed -i'' '' 's/../.../' ${file}
> 
> IIRC those sed's with an optional backup suffix (Linux, OpenBSD) will
> accept the immediately following empty string and accept the next
> empty word as an empty command, while our getopt will effectively
> ignore the rest of the -i word and use the following optarg as usual.

Unfortunately, times appear to have changed, at least on ubuntu-18.04:

$ sed -i'' '' "/^# /d" temp.tmp
sed: can't read /^# /d: No such file or directory

Gary