portable sed in place editing

[Dominique_71]

Something that was not obvious to me to find. It is 3 possibilities to make an in place file sed editing:

1) On linux, we can use:


Code:

sed -i 'sed command' file


If file don't exist, no empty file will be created. But that will not work on some systems, as example freebsd.

2) On both linux and freebsd, we can add a .suffix to -i:


Code:

sed -i.bak 'sed command' file


If file don't exist, no empty file will be created.

3) It is not in place editing but the result is the same, and it is the safest way to do it - on both linux and freebsd, we can use redirection and a temporary file:


Code:

sed 'sed command' file > file.tmp mv -f file.tmp file


or


Code:

sed 'sed command 1' file > file.tmp sed 'sed command 2' file.tmp > file


If file don't exist, that will create an empty file, which can cause nasty bugs. That imply it is best and necessary to test if file exist and run these 2 commands only if it exist.

_________________
"Confirm You are a robot." - the singularity

[Hu]

If you really don't want to rely on GNU sed, you could rely on redirection ordering instead.

[Dominique_71]

Thanks for the tips Hu. As fvwm-crystal's main contributor, I was asked if it can support freebsd and is looking at it. Almost all of the needed fixes was a few path changes with the Makefile, and some of the sed calls.
_________________
"Confirm You are a robot." - the singularity

[Hu]

I think most of the BSDs can have GNU sed, though they tend to install it as gsed, reserving the name sed for the BSD sed. Perhaps you would be better off just using gsed -i instead of adding logic to work around BSD sed not supporting -i? At least on Gentoo, gsed exists as an alias for the GNU sed installed as sed, so if you use gsed, you can do that without regard to BSD vs Gentoo. I cannot comment on whether other Linux distributions provide gsed as an alias.

[Dominique_71]

[eschwartz]