sed -i empty argument compatibility issue

[Gary Aitken]

On 3/5/21 10:15 PM, Kyle Evans wrote:
> On Fri, Mar 5, 2021 at 11:12 PM Gary Aitken <freebsd at dreamchaser.org> wrote:
>>
>> 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
>>
> 
> Oh, sorry. Try slapping with an -e:
> 
> $ sed -i'' '' -e "/^# /d" temp.tmp

nope:

$ sed -i'' '' -e "/^# /d" temp.tmp
sed: can't read : No such file or directory
$ !ls
ls -lt temp.tmp*
-rw-rw-r-- 1 garya garya 86 Mar  6 05:29 temp.tmp
-rw-rw-r-- 1 garya garya 86 Mar  5 20:45 temp.tmp_org

Gary