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Old 02-02-2010, 09:01 AM   #1
Registered: Oct 2009
Posts: 40

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SED - substitute a word only in a certain line

Hi everybody,

I tried to use the command:

sed -i ''$line_number',/port/s/port/portMARKED/' file

to substitute the word "port" by the word "portMARKED" at the specific line that is saved in "line_number". The substitution happens, but it is copying my line twice... and I have no idea why...

I need to make a single substitution of one word for another at a certain line in my text file. Would somebody know how I could do that?

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Old 02-02-2010, 09:20 AM   #2
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sed "${line_number}s/port/portMARKED/" infile

I'm not sure why you added the ,/port/ part, it is not needed.

General form (substitute with address range): sed '[address1[,address2]]s/pattern/replacement/[flags]' infile

flags is not used in your example, but could be g (global replace on whole line).

Hope this helps.
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Old 02-02-2010, 09:27 AM   #3
Registered: May 2004
Location: UK
Distribution: Debian, Ubantu, CentOS
Posts: 146

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Some handy sed examples:

From that link:
 # substitute (find and replace) "foo" with "bar" on each line
 sed 's/foo/bar/'             # replaces only 1st instance in a line
 sed 's/foo/bar/4'            # replaces only 4th instance in a line
 sed 's/foo/bar/g'            # replaces ALL instances in a line
you have already seen the use of the
option for inserting text to the file.
Not sure what the other parts were (or if you had got confused with the sed instructions as I often do).

if I take file (tmptxt.txt):
text1 text text
text2 text text
text3 text3 text3
And run:
sed -i '2 s/text/textMARKED/' tmptxt.txt
I get:
text1 text text
textMARKED2 text text
text3 text3 text3

in your script you may need to replace single quotes with double quotes.
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Old 02-02-2010, 09:30 AM   #4
Registered: Oct 2009
Posts: 40

Original Poster
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Thanks a lot guys!

I saw the comma in another example, but now I understood why it should not be there.


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