Change Specific Line of a File

msb65 · #1 (**permalink**) 08-18-2008

Hi everyone,

I am attempting to do something that should be very simple. How do I replace a specific line of a file with different text, and then save that file to its original name? I believe I want to use the sed command with the c option, but I after trying many times, I can't get the right syntax. I am using bash.

Mike

jim mcnamara · #2 (**permalink**) 08-18-2008

Code:

different_text="this is the new text"
awk -v diff="$different_text" '{ if(NR==4) { print diff}
                              else {print $0} } ' filename > newfilename

era · #3 (**permalink**) 08-18-2008

Code:

sed '42c\'"I am the walrus" file >newfile

msb65 · #4 (**permalink**) 08-18-2008

Hi,

Yes I was trying to something similar. However, that still does not work. Is that the syntax for bash?

era · #5 (**permalink**) 08-18-2008

Works here, Ubuntu 7.something, bash 3.2.13. The sed version is what decides whether it works or not, though. I have GNU sed version 4.1.5

Code:

vnix$ sed '4c\'"I am the walrus" /etc/motd
Linux left 2.6.20-17-386 #2 Thu Jul 10 00:02:05 UTC 2008 i686

The programs included with the Ubuntu system are free software;
I am the walrus
individual files in /usr/share/doc/*/copyright.

Ubuntu comes with ABSOLUTELY NO WARRANTY, to the extent permitted by
applicable law.

Try putting the change on a different line:

Code:

sed '42c\
I am the walrus' file >newfile

Yes, you would put a backslash and a newline between "42c" and "I am the walrus". Yes, that's right. No, I'm not kidding. (Nothing personal, it's just that the normal reaction to this instruction is "I tried it and it doesn't work." "So did you put a backslash and a newline between the two lines?" "No, was I supposed to?")

msb65 · #6 (**permalink**) 08-18-2008

Perhaps i am not going about this correctly. Here is my "test file":

$cat test.txt
coo
coo
ca
choo
$

Let's say I simply want to replace the first line (coo) with koo.

With the above suggestion:

$sed '1c\'"koo" test.txt
sed: 1: "1c\koo": extra characters after \ at the end of c command

Putting a space before "koo" yields:

$sed '1c\' "koo" test.txt
sed: koo: No such file or directory
coo
ca
choo

I get closer by typing:

$sed '1c\
> koo' test.txt
koocoo
ca
choo

But it's still not right. I am using the bash that comes with OS X Leopard. Any ideas on what's going wrong?

era · #7 (**permalink**) 08-18-2008

Probably your version of sed is different; OSX is traditionally BSD based.

Try this:

Code:

sed '1c\
koo\
' test.txt

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