[SOLVED] Sed to replace range of text at specific coordinates

Drosera_capensis · 09-01-2020, 09:02 AM

Hello everyone,

I wish to edit a document, replacing a range of characters with another range of text.
For example the following input has to be modified between character 3 and 7 with "1234".

Input:

Quote:

abcdefghijklmnopqrstuvwxyz

Output:

Quote:

ab1234hijklmnopqrstuvwxyz

I was thinking about using the command sed to do so, but it seems it only replace lines by ranges addresses, and not characters. https://www.gnu.org/software/sed/man...ange-Addresses

Would anyone know how to do the substitution?

berndbausch · 09-01-2020, 09:15 AM

Quote:

Originally Posted by Drosera_capensis

For example the following input has to be modified between character 3 and 7 with "1234".

If the above is the precise description, this is a solution:

Code:

sed 's/^\(..\)...../\11234'

EDIT:
This should also work. Didn't try.

Code:

sed 's/^\(..\).\{5\}/\11234'

boughtonp · 09-01-2020, 09:26 AM

This can be done directly in the shell with parameter expansion...

Code:

$ myvar='abcdefghijklmnopqrstuvwxyz'
$ echo "${myvar:0:2}1234${myvar:7}"
abc1234hijklmnopqrstuvwxyz

Drosera_capensis · 09-01-2020, 09:32 AM

Thank you berndbausch, the two commands are indeed working as following:

Quote:

sed 's/^$..$...../\11234/'
sed 's/^$..$.\{5\}/\11234/'

However, I am going to use these commands on a more complex script with variables ($s for starting position, $e for ending position. So the range would be $s-$e).
Would you know how replace the dots "." on the commands above?

berndbausch · 09-01-2020, 09:38 AM

Something like

Code:

s1=$((s-1))
diff=$((e-s))
sed "s/^\(.\{$s1\}\).\{$diff\}/\11234"

This becomes increasingly unreadable. Perhaps variable substitution works with non-constant positions?

Drosera_capensis · 09-01-2020, 09:43 AM

Thank you boughtonp and berndbausch, your scripts are indeed working.

I will try to build my script with the simple substitution command, but will use the sed script if the former does not work.

Thanks!

boughtonp · 09-01-2020, 09:48 AM

Quote:

Originally Posted by berndbausch

This becomes increasingly unreadable. Perhaps variable substitution works with non-constant positions?

Yep, and is also why the complete problem / context should be provided up-front.

Variable substitution doesn't even need a separate variable to go from position to offset - can simply write:

Code:

echo "${myvar:0:$start-1}1234${myvar:$end}"