[SOLVED] What does '/m64=/' mean in the sed command?

NuttyJamie · 01-13-2021, 03:43 PM

Greetings folks!

I saw this type of sed command while following the LinuxFromScratch book's instructions.

First, the book says:

Quote:

If building on x86_64, change the default directory name for 64-bit libraries to “lib”:

And the code is:

Code:

case $(uname -m) in
  x86_64)
    sed -e '/m64=/s/lib64/lib/' \
        -i.orig gcc/config/i386/t-linux64
  ;;
esac

I knew sed's replace command format, such as s/<source text>/<replace text>/gc, and so I know what this whole code ends up doing, but I've never seen the middle part of it before.

Code:

sed -e '/m64=/s/lib64/lib/' \

What exactly does the /m64=/ do?
I searched through several sed tutorials and found nothing similar.

berndbausch · 01-13-2021, 03:53 PM

Quote:

Originally Posted by NuttyJamie

Code:

sed -e '/m64=/s/lib64/lib/' \

What exactly does the /m64=/ do?

It selects the lines that sed will process. In this case, the substitution is performed in all lines that contain "m64=".

Quote:

I searched through several sed tutorials and found nothing similar.

See https://www.gnu.org/software/sed/man...esses-overview.

NuttyJamie · 01-13-2021, 04:22 PM

Quote:

Originally Posted by berndbausch

It selects the lines that sed will process. In this case, the substitution is performed in all lines that contain "m64=".

Oh, Now it seems clear. I thought it was a sed's own option or sub-command or similar to regular expression...

what a stupid.

Quote:

Originally Posted by berndbausch

See https://www.gnu.org/software/sed/man...esses-overview.

The GNU manual! Why didn't I think of that?

I just saw it for the first time and it's very detailed and useful. Not only solved a problem, but I also learned that there was a manual written by FSF.
It was a lot of help. Thank you very much.

berndbausch · 01-13-2021, 05:36 PM

Quote:

Originally Posted by NuttyJamie

I just saw it for the first time and it's very detailed and useful. Not only solved a problem, but I also learned that there was a manual written by FSF.

All GNU software is documented. In my opinion, the sed manual is fairly well-written.

NuttyJamie · 01-13-2021, 06:27 PM

Quote:

Originally Posted by berndbausch

All GNU software is documented.

That's just awesome!
I am happy because there are many documents to study.

Quote:

In my opinion, the sed manual is fairly well-written.

I totally agree.

tofino_surfer · 01-14-2021, 01:53 PM

Quote:

I searched through several sed tutorials and found nothing similar.

It's in the sed manpage itself under the section "Addresses"

Code:

Addresses
       Sed  commands can be given with no addresses, in which case the command will be executed for all input lines; with one address, in which case the command will only be exe‐
       cuted for input lines which match that address; or with two addresses, in which case the command will be executed for all input lines which match the  inclusive  range  of
       lines  starting from the first address and continuing to the second address.  Three things to note about address ranges: the syntax is addr1,addr2 (i.e., the addresses are
       separated by a comma); the line which addr1 matched will always be accepted, even if addr2 selects an earlier line; and if addr2 is a regexp, it will not be tested against
       the line that addr1 matched.
...
       /regexp/
              Match lines matching the regular expression regexp.  Matching is performed on the current pattern space, which can be modified with commands such as ``s///''.

So therefore sed -e 's/lib64/lib/' has no address and the s// operates on all input lines.

Conversely sed -e '/m64=/s/lib64/lib/' has a regular expression address of /m64=/ so the s// construct only works on lines matching /m64=/.