2

Is there any undocumented flag in AIX's sed implementation that allows for in-place editing in the same way as with e.g. GNU sed? The manual shows no flag for this operation, which is one of the most useful ones in other sed implementations.

  • 1
    If you don't see it in the man page, you can be pretty sure it doesn't exist. Just use sed 's/a/b/' foo > bar && mv bar foo – terdon Jan 30 '14 at 14:19
  • 1
    Use perl -pi instead. – Stéphane Chazelas Jan 30 '14 at 14:41
  • @StephaneChazelas is Perl installed on AIX? – terdon Jan 30 '14 at 14:56
  • Just one thing to note regarding @terdon's suggestion: that may result a foo file with different owner/permissions than the original one. – manatwork Jan 30 '14 at 15:03
  • @manatwork so will sed -i (at least on my Debian). It works by creating a temp file in the backgroud and renaming it to the original file's name so it will be owned by whoever ran the sed. – terdon Jan 30 '14 at 15:06
3

you can use perl to do it:

perl -p -i.bak -e 's/old/new/g' test.txt

It's going to create a .bak file.

Or without a .bak file :

perl -pi -e  's/old/new/g' test.txt

Or install sed-4.1.1 RPM from here.

3

This is not possible on AIX even with the sed tool installed.
You do need to use a temp file like suggested by terdon in comments to the question:

sed 's/a/b/' foo > bar && mv bar foo

You could also use ed which does inline editing.

  • Why would it not be possible with GNU sed installed? – Stéphane Chazelas Jan 30 '14 at 14:42
  • well the GNU provided by AIX not the one you can compile see also ==> stackoverflow.com/questions/7232797/… – Kiwy Jan 30 '14 at 14:43
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    -i was added in sed-3.95 (2002). IBM offers 3.0.2, 4.0.7 and 4.1.1 AFAICT. Unless you get the older one, you'll get -i. Also note that you can get packaged version of GNU sed for AIX from other sources. – Stéphane Chazelas Jan 30 '14 at 15:08
  • Well it means my admin system never updated since 2002 I guess. because even with AIX 6.1 I don't have the possibility to use that switch – Kiwy Jan 30 '14 at 15:17
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    @StéphaneChazelas I was reading between the lines of your comment from 2 years ago: "-i was added in sed-3.95 (2002). IBM offers 3.0.2, 4.0.7 and 4.1.1 AFAICT" the implication that you saw recent versions of AIX offering sed's that supported -i. – Jeff Schaller Apr 20 '16 at 15:25
2

To use a standard compliant sed, which does not have -i, to do in-place editing, in such a way that permissions, file ownerships and some other metadata are not modified and hard links and symlinks are not broken:

cp file file.tmp &&
sed 'expression' file.tmp >file &&
rm -f file.tmp

This creates a temporary copy of the file we want to edit, and then applies the sed command to this copy while redirecting the result to the original filename.

Redirecting to the original filename will truncate and rewrite that file, and since the file is not first deleted and recreated, it will retain most of its metadata.

  • fwiw, that's not what sed is doing. sed is redirecting the output to a temp file, copy through the permissions and finally rename the temp file to the original. That will change the file's inode and wipe some precious metadata but a) will not trash the file's content if the sed -i command was interrupted or failed b) will not trash the file's content if more that one sed -i was run on the same file at the same time. More details and ranting here. – mosvy Mar 12 at 14:15
  • @mosvy All true. The way I have arranged the commands in my answer will ensure that the original contents (at least) is still available in the temporary file if the sed fails. – Kusalananda Mar 12 at 14:40
-1
  1. Define a variable and use a subshell to execute sed and redirect to a file. Very important use " (double quote) to protect the variable $value:

    value=$(sed 's/old/new/g' file) && echo "$value" > file
    

Or

  1. Execute echo with a subshell you going to execute 'sed' and redirect to a file:

    echo "$(sed 's/old/new/g' file)" > file
    
  • That is just a convoluted way of doing what the comment by @terdon does. Better yet, grab the GNU sed and install that. – vonbrand Mar 1 '16 at 14:53
  • option #2 will most likely truncate 'file' before reading from it -- be careful! – Jeff Schaller Mar 1 '16 at 14:55
  • @JeffSchaller : no, because the subshell should end before print opens its fd. – Mat M Jul 19 '18 at 12:53
  • Use print with ksh or you will lose the line feeds. – Mat M Jul 19 '18 at 12:54
  • @vonbrand : it avoids creating a temp file, and it is sometimes a requirement – Mat M Jul 19 '18 at 12:55

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