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linux command sed


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Hi all !

 

Can someone please explain what the following command does:-

sudo sed -i s,scotchbox.local,$DOMAIN,g /etc/apache2/sites-available/$DOMAIN.conf
sudo sed -i s,/var/www/public,/var/www/$DOMAIN/public,g /etc/apache2/sites-available/$DOMAIN.conf

I can across these commands in here.

 

I have tried them out in the terminal as a modified example :- sudo sed -i, s,www,the,g test.txt.

where test.txt has 2 lines of some text containing the word 'the' a couple of times. The command seems to do nothing. There is no change in test.txt.

 

I cannot get any example of sed -i, s on google. In fact i cannot get a similar example of sed anywhere on google. But then i believe sed is extremely versatile and has tons of usages. 

 

Grateful for any help.

Thanks all.

 

 

 

 

 

 

 

 

 

 

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man sed

 

 

-i[sUFFIX], --in-place[=SUFFIX]

 

edit files in place (makes backup if extension supplied). The default operation mode is to break symbolic and hard links. This can be changed with --follow-symlinks and --copy.

s/regexp/replacement/

 

Attempt to match regexp against the pattern space. If successful, replace that portion matched with replacement. The replacement may contain the special character & to refer to that portion of the pattern space which matched, and the special escapes \1 through \9 to refer to the corresponding matching sub-expressions in the regexp.

So basically it modifies the given files to make a couple replacements.

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I have tried them out in the terminal as a modified example :- sudo sed -i, s,www,the,g test.txt.

where test.txt has 2 lines of some text containing the word 'the' a couple of times. The command seems to do nothing. There is no change in test.txt.

Try putting "www" in it instead.
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Hi kicken and requinix, 

 

Thanks for the reply.

 

@kicken : Yes it was me clear that it was trying to make a replacement of sorts but the command seems not to do anything. 

@ requinix : No this - (with "www") - does not work either. 

 

Thanks.

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@ requinix : No this - (with "www") - does not work either.

root@*:~# cat test.txt
[quote name="ajoo" post="1543020" timestamp="1487487301"]
I have tried them out in the terminal as a modified example :- sudo sed -i, s,www,the,g test.txt.
where test.txt has 2 lines of some text containing the word 'the' a couple of times.The command seems to do nothing.
There is no change in test.txt.
[/quote]
Try putting "www" in it instead.

root@*:~# sed -i s,www,the,g test.txt
root@*:~# cat test.txt
[quote name="ajoo" post="1543020" timestamp="1487487301"]
I have tried them out in the terminal as a modified example :- sudo sed -i, s,the,the,g test.txt.
where test.txt has 2 lines of some text containing the word 'the' a couple of times.The command seems to do nothing.
There is no change in test.txt.
[/quote]
Try putting "the" in it instead.

root@*:~#
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Hi requininx, 

 

In all cases it simply makes an exact copy of the given file. I am using "test.txt" and it creates a "test.txt," file after the command is run but makes no string substitutions.

 

Maybe that's what the -i is there for.

 

 

Ok I got it after some more tries. This works :

sudo sed -i, s,the,abc,g test.txt.

It saves the original file as a copy while actually modifying the orignal file with the string substitutions..

 

Thanks.

Edited by ajoo
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  • Solution

The test.txt, file is not supposed to change, that's the backup in case you messed up. The original test.txt is the one that gets changed.

 

kicken@web1:~$ echo 'Visit www.example.com today!' > test.txt
kicken@web1:~$ sed -i, s,www,the,g test.txt
kicken@web1:~$ cat test.txt
Visit the.example.com today!
kicken@web1:~$ cat test.txt,
Visit www.example.com today!
kicken@web1:~$
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