Regular Expression

sumitsahay · 10-09-2018, 02:29 AM

Hi All,

I struggling to replace special characters from string below is the string example.

"\nhostname \n\r"

I want to remove \n and \r from the string, as of now unable to do so.

Looking forward for reply.

Regards
Sumit Sahay
7044112109

l0f4r0 · 10-09-2018, 03:00 AM

Have you tried tr with option -d?

sumitsahay · 10-09-2018, 03:46 AM

Quote:

Originally Posted by l0f4r0

Have you tried tr with option -d?

Thanks for your reply.
I was trying below one,

sed -i 's/"\nhostname \n\r"/"hostname"/g' known_host.txt

Regards
Sumit Sahay

syg00 · 10-09-2018, 04:04 AM

sed doesn't get to see the newline (\n) - it is stripped before the record is passed to be processed. Hence your regex will never match.

l0f4r0 · 10-09-2018, 04:08 AM

Quote:

Originally Posted by sumitsahay

I was trying below one,

Code:

sed -i 's/"\nhostname \n\r"/"hostname"/g' known_host.txt

As syg00 said, sed works with lines one by one so "\n" will never match your regex...except if you modify the pattern space (with instruction "N" in your case).
...But I warn you it's easier with tr. Your choice

sumitsahay · 10-09-2018, 04:24 AM

Quote:

Originally Posted by syg00

sed doesn't get to see the newline (\n) - it is stripped before the record is passed to be processed. Hence your regex will never match.

Could you please navigate me to achieve the output.

I want to replace \n and \r from the string.

l0f4r0 · 10-09-2018, 04:41 AM

I've already give you a way to achieve what you want with sed (if I were you I would read some documentation about pattern space modification, for example https://www.gnu.org/software/sed/man...ine-techniques). You need to associate instructions "N" and "s" (+"p" if you used option "-n").
But as stated above, it's much easier with tr applied to the content of your variable...

sumitsahay · 10-09-2018, 07:20 AM

Quote:

Originally Posted by l0f4r0

I've already give you a way to achieve what you want with sed (if I were you I would read some documentation about pattern space modification, for example https://www.gnu.org/software/sed/man...ine-techniques). You need to associate instructions "N" and "s" (+"p" if you used option "-n").
But as stated above, it's much easier with tr applied to the content of your variable...

Sorry, not getting your point, I was trying to use tr to replace \n and \r but for me it is not working.

l0f4r0 · 10-09-2018, 07:47 AM

Quote:

Originally Posted by sumitsahay

Sorry, not getting your point, I was trying to use tr to replace \n and \r but for me it is not working.

Ok, give us the command you tried and its output

BW-userx · 10-09-2018, 07:56 AM

if the \n and \n\r are explicit within the text then try this, you'll have to mod it for your own usage.

Code:

someline="\nsometinghere\n\r"

$ results="$(echo $someline | sed 's|\\nsometinghere\\n\\r|somethinghere|')"

$ echo $results
somethinghere

escaping the escapes. some tr commands and how tos
http://www.softpanorama.org/Tools/tr.shtml

l0f4r0 · 10-09-2018, 08:03 AM

Quote:

Originally Posted by BW-userx

if the \n and \n\r are explicit within the text then try this, you'll have to mod it for your own usage.

Code:

someline="\nsometinghere\n\r"
$ results="$(echo $someline | sed 's|\\nsometinghere\\n\\r|somethinghere|')"
$ echo $results
somethinghere

escaping the escapes. some tr commands and how tos
http://www.softpanorama.org/Tools/tr.shtml

Doesn't work for me

BW-userx · 10-09-2018, 08:06 AM

Quote:

Originally Posted by l0f4r0

Doesn't work for me

you assigned a variable with exactly \nsomethinghere\n\r then ran that code to match it, and it did not work? humm I find that hard to take in as it should not matter across distros

Code:

someline="\nhereweAre\n\r"
userx@manjaroieo:~
$ echo $someline
\nhereweAre\n\r


userx@manjaroieo:~
$ results="$(echo $someline | sed 's|\\nhereweAre\\n\\r|somethinghere|')"
userx@manjaroieo:~
$ echo $results
somethinghere

check your code.

l0f4r0 · 10-09-2018, 08:18 AM

Quote:

Originally Posted by BW-userx

you assigned a variable with exactly \nsomethinghere\n\r then ran that code to match it, and it did not work? humm I find that hard to take in as it should not matter across distros
check your code.

Here is my output:

Code:

someline="\nhereweAre\n\r"
echo $someline

hereweAre

results="$(echo $someline | sed 's|\\nhereweAre\\n\\r|somethinghere|')"
echo $results

hereweAre

I think it depends on echo implementation

@sumitsahay: Does it work for you?

BW-userx · 10-09-2018, 09:19 AM

Quote:

Originally Posted by l0f4r0

Here is my output:

Code:

someline="\nhereweAre\n\r"
echo $someline

hereweAre

results="$(echo $someline | sed 's|\\nhereweAre\\n\\r|somethinghere|')"
echo $results

hereweAre

I think it depends on echo implementation

@sumitsahay: Does it work for you?

that's insane, I've never seen that before, your var assignment is quoted, and it still does not add the \n and \n\r to it.