topic Re: Best sed usage in Operating System - Linux

Best sed usage

lawrenzo_1 — Mon, 12 May 2008 13:43:33 GMT

Hi all,

I have 3 different parameters to change in a file and want to use sed, what is the best way to change the value of 3 different strings from the same file - then replace the file ie:

FILE=FILE.cfg
userbase=xyz
timeout=5
defaultentry=local

# cat $FILE | sed -e 's/userbase=xyz/userbase=abc/;
-e s/timeout=5/timeout=60/ -e s/defaultentry=local/defaultentry/' > ${FILE}.tmp

cp ${FILE}.tmp ${FILE}

is this the best way or is there a more logical method?

thanks

Chris

Re: Best sed usage

James R. Ferguson — Mon, 12 May 2008 13:52:55 GMT

Hi Chris:

If you want to do this with 'sed', do:

# sed -e 's/userbase=xyz/userbase=abc/;s/timeout=5/timeout=60/;s/defaultentry=local/defaultentry/' ${FILE} > ${FILE}.tmp

# mv ${FILE}.tmp ${FILE}

Notice that you do NOT need to run a 'cat' process which 'sed' then reads from a pipe. This is a waste of a process.

Notice too the change I made in the 'sed' syntax. A semicolon between the substitution commands with one '-e' switch ahead of the arguments.

Of course, Perl can do an inplace update eliminating the 'mv' step :-)

Regards!

...JRF...

Re: Best sed usage

Steven Schweda — Mon, 12 May 2008 14:22:45 GMT

> Notice too the change I made in the 'sed'
> syntax.

Which makes it harder to read, but does it
have any other (real) benefits?

Re: Best sed usage

James R. Ferguson — Mon, 12 May 2008 14:32:08 GMT

Hi (again):

> Steven: > Notice too the change I made in the 'sed' syntax. Which makes it harder to read, but does it have any other (real) benefits?

In my opinion, this isn't harder to read. To me, is is more consistent with a script and a script's syntax (which the '-e' signifies in the first place). Moreover, the syntax becomes exactly compatabile to a Perl script:

# perl -pe 's/userbase=xyz/userbase=abc/;s/timeout=5/timeout=60/;s/defaultentry=local/defaultentry/' file

...which then leads to doing Perl in-place updates, thereby saving the 'mv step:

# perl -pi.old -e 's/userbase=xyz/userbase=abc/;s/timeout=5/timeout=60/;s/defaultentry=local/defaultentry/' file

...which preserves the original file as "file.old" while leaving the updated file as "file".

Regards!

...JRF...

Re: Best sed usage

lawrenzo_1 — Mon, 12 May 2008 14:41:57 GMT

here is what I initally wrote:

userbasedn="userbasedn:ou=people,ou=nis,ou=eu,o=unilever,c=gb"
ldaptimeout="ldaptimeout:5"
defaultentrylocation="defaultentrylocation:local"

sed -e 's/userbasedn.*$/'${userbasedn}'/' -e 's/.ldaptimeout.*$/'${ldaptimeout}'/' -e 's/^defaultentrylocation.*$/'${defaulte
ntrylocation}'/' ${LDAPCFG} > ${LDAPCFGBCK}

and this works however your syntax the command waits ie:

sed -e 's/userbasedn.*$/'${userbasedn}'/';'s/.ldaptimeout.*$/'${ldaptimeout}'/';'s/^defaultentrylocation.*$/'${defaultentrylocation}'/' ${LDAPCFG} > ${LDAPCFGBCK}

what have i missed?

Thanks

Re: Best sed usage

James R. Ferguson — Mon, 12 May 2008 15:24:18 GMT

Hi (again) Chris:

Ah, so you changed the example :-)

OK, if you are going to use interpolated variables, put them in double-quotes so that the shell expands them:

# sed -e "s/userbasedn.*$/"${userbasedn}"/;s/.ldaptimeout.*$/"${ldaptimeout}"/;s/^defaultentrylocation.*$/"${defaultentrylocation}"/" file

Regards!

...JRF...

Re: Best sed usage

Steven Schweda — Mon, 12 May 2008 15:41:52 GMT

> In my opinion, this isn't harder to read.

Whateveryousay.

Re: Best sed usage

OldSchool — Mon, 12 May 2008 18:59:02 GMT

of course, the original posting:

sed -e 's/userbase=xyz/userbase=abc/;
-e s/timeout=5/timeout=60/ -e s/defaultentry=local/defaultentry/' > ${FILE}.tmp

doesn't / wont run anyway...it doesn't understand the "-e" inside the quotes...believe the o.p. is confusing this with the "multiple pattern" in grep

Re: Best sed usage

James R. Ferguson — Mon, 12 May 2008 23:05:23 GMT

Hi Chris:

> OldSchool: of course, the original posting...doesn't / wont run anyway...it doesn't understand the "-e" inside the quotes...believe the o.p. is confusing this with the "multiple pattern" in grep

True, but this is legal (and looks like a multiple option/multiple pattern 'grep'):

# sed -e 's/userbase=xyz/userbase=abc/' -e 's/timeout=5/timeout=60/' -e 's/defaultentry=local/defaultentry/' file

Regards!

...JRF...

Re: Best sed usage

Dennis Handly — Tue, 13 May 2008 00:54:32 GMT

>is this the best way or is there a more logical method?

Other than JRF's mv and removal of cat, I would go with multiple -e scripts that he had at the end.

I typically wouldn't use the jammed up embedded commands but having a blank after each ";" may make Steven happy. :-)

>Steven: Which makes it harder to read, but does it have any other (real) benefits?

Well, as OldSchool points out, JRF's works, and the original didn't. I would typically use multiple -e. You could put the script in a file (-f script-file) or use:
sed -e 's/userbase=xyz/userbase=abc/
s/timeout=5/timeout=60/
s/defaultentry=local/defaultentry/' ${FILE} > ${FILE}.tmp

A file wouldn't allow Lawrenzo's ${userbasedn} substitution, unless it was a here document.

Re: Best sed usage

lawrenzo_1 — Tue, 13 May 2008 13:01:56 GMT

lots of discussion here and thanks all.

Chris.