topic Re: A few sed questions in Operating System - HP-UX

A few sed questions

Gemini_2 — Wed, 06 Aug 2008 20:00:09 GMT

how do you insert a string and a **blank line** by using sed.

for example

input
*******************
current
**********************

output
*****************
before

current
******************
I have the following
sed "/^current/i before " $file

but it didnt insert a blank line right after the string "before" thank you

Re: A few sed questions

James R. Ferguson — Wed, 06 Aug 2008 20:37:24 GMT

Hi:

Perl is so much easier:

# perl -ple 'print "before\n" if /^current/' file

Regards!

...JRF...

Re: A few sed questions

James R. Ferguson — Wed, 06 Aug 2008 20:56:20 GMT

Hi (again) Gemini:

# cat mysed
#!/usr/bin/sed -f
/^current/{
i\
newline with blank line
i\

}

...run as :

# ./mysed file

Note that I used two (2) (i)insert operators.

Regards!

...JRF...

Re: A few sed questions

Gemini_2 — Wed, 06 Aug 2008 22:12:59 GMT

Thanks for your clear explaination. I now learned how to use "i\" I see, it is one line at at time.

May I ask you another question? you can use sed, or any shell commands. I have been trying differerent combinations, but I can not get it right...

I want to parse the following input file. basically, I want to search for "install:", then add a new line right before "endif"

I tried the following, but "N" only read the next line, what if I am not sure how many lines, but I want to add a line right before "endif" in the "install:" block.

thanks for spending your time to educate me!

sed -e '/^install:/{
N
s,endif,new string,
#}' $file

input
******************************
install: ap_dir
some lines..
endif

preinstall: pub_dir
some lines..
endif
*******************

Re: A few sed questions

James R. Ferguson — Wed, 06 Aug 2008 22:55:29 GMT

Hi (again):

Try this:

# cat mysed
#!/usr/bin/sed -f
/^install/,/^endif/ {
/^endif/ {
i\
newline ADDED
}
}

...using your input:

# cat somestuff
install: ap_dir
some lines..
endif

preinstall: pub_dir
some lines..
endif

...run as:

# ./mysed somestuff
install: ap_dir
some lines..
newline ADDED
endif

preinstall: pub_dir
some lines..
endif

Regards!

...JRF...

Re: A few sed questions

Gemini_2 — Wed, 06 Aug 2008 23:10:45 GMT

I can not believe it! it works soo beautifully!!

thank you so much!!!

btw, do you have the sed/awk book? where can I learn this trick!!

thanks a million again!!!!!!!!

thank you!!!

Re: A few sed questions

James R. Ferguson — Wed, 06 Aug 2008 23:27:23 GMT

Hi (again) Gemini:

I'm happy that I could help.

You might try:

http://www.gnu.org/software/sed/manual/

...and O'Reilly's :

http://oreilly.com/catalog/9781565922259/

...and in various places and various forms:

http://student.northpark.edu/pemente/sed/sed1line.txt

Regards!

...JRF...

Re: A few sed questions

James R. Ferguson — Wed, 06 Aug 2008 23:29:18 GMT

Hi Gemini:

...and a few credits for the last solution I posted would be appreciated too :-))

Regards!

...JRF...

Re: A few sed questions

Gemini_2 — Wed, 06 Aug 2008 23:30:25 GMT

thanks a million again!

you really made my day!!!

I will check the reference sites!

but, I have searched the website, I think that your example is the best, I have not seen on like that!

Re: A few sed questions

Dennis Handly — Thu, 07 Aug 2008 03:13:42 GMT

Note JRF's solution uses scripts whose interpreter is the command sed. awk also works like this.
(One reason for doing it, is to be able to have single quotes inside.)

But you can do the whole thing inside a shell script too:
$ sed -e '
/^current/i\
before\
' $file

>I want to parse the following input file. I want to search for "install:", then add a new line right before "endif"

I would suggest you not use sed for something this complicated. awk is much easier to understand.

awk '
/^install:/ { flag = 1 }
/^endif/ && flag {
print "some new stuff"
flag = 0
}
{ print }' $file

Re: A few sed questions

James R. Ferguson — Thu, 07 Aug 2008 10:00:13 GMT

Hi (again) Gemini:

> Dennis: I would suggest you not use sed for something this complicated. awk is much easier to understand.

While 'sed' was not my prefereence either, I would use Perl for the second solution:

# perl -ple 'if (/^install/../^endif/) {print "newline ADDED" if /^endif/}' file

...short, sweet and can be inlined in a shell script.

Regards!

...JRF...

Re: A few sed questions

Gemini_2 — Wed, 13 Aug 2008 19:37:37 GMT

One more sed question

input
*************************
instal: a b c
ifeq
whatever
endif
********************

I want to do string substition on "install:"
but only if there is a "ifeq" right underneath it... how do I do that?

thank you.

Re: A few sed questions

James R. Ferguson — Wed, 13 Aug 2008 19:51:03 GMT

Hi (gemini:

Regarding your newest question, I think you need to look to Perl or 'awk', so:

# perl -nle 'if (/^ifeq/) {$hold=~s/install/NEWINSTALL/};print $hold if defined $hold;$hold=$_' file

...using this input:

# cat input
install: a b c
ifeq
whatever
endif
install: a b c
ofeq
whatever
endif
install: a b c
ifeq
whatever
endif

...the Perl script yields:

NEWINSTALL: a b c
ifeq
whatever
endif
install: a b c
ofeq
whatever
endif
NEWINSTALL: a b c
ifeq
whatever

Regards!

...JRF...

Re: A few sed questions

Gemini_2 — Wed, 13 Aug 2008 20:01:01 GMT

thanks for your speedy reply.

So, it can not be done in sed, but it can be done in perl right?

no problem, I can use perl in the shell script, i just want to be sure!

Re: A few sed questions

Gemini_2 — Wed, 13 Aug 2008 20:02:30 GMT

hmm...I submit 10 point, how come it become 0 point.

when you reply, I will submit the right point again.

Re: A few sed questions

James R. Ferguson — Wed, 13 Aug 2008 20:06:13 GMT

Hi (again):

Thanks! Glad to help!!!

Regards!

...JRF...

Re: A few sed questions

Gemini_2 — Wed, 13 Aug 2008 20:07:58 GMT

btw, if you dont mind, can you tell me how you would do it in awk?

Re: A few sed questions

James R. Ferguson — Wed, 13 Aug 2008 20:11:01 GMT

Hi Gemini:

> So, it can not be done in sed, but it can be done in perl right?

Well, in fairness, I wouldn't say that it can't be done with 'sed' --- a 'sed' guru probably could, but I'm not that. A good 'sed' guide, including some very advanced handling is here:

http://www.gnu.org/software/sed/manual/sed.html

Regards!

...JRF...

Re: A few sed questions

James R. Ferguson — Wed, 13 Aug 2008 20:32:23 GMT

Hi Gemini:

OK, 'awk' looks like this:

# awk '{if (/^ifeq/) {sub("install","NEWINSTALL",hold)};if (NR>1) {print hold};hold=$0}' file

...with the same example I used for the Perl snippet.

Regards!

...JRF...

Re: A few sed questions

Dennis Handly — Wed, 13 Aug 2008 21:02:12 GMT

>JRF: awk looks like this:

You are missing the last line:
awk '
{
if (/^ifeq/) {
sub("install","NEWINSTALL",hold)
}
if (NR>1) {print hold}
hold=$0
}
END {print hold}' file