How to replace all but the first 3 characters with sed?


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# 1  
Question How to replace all but the first 3 characters with sed?

This seems like it should be an easy problem, but for some reason I am struggling with the solution.
I simply want to replace all characters after the first 3 characters with another character, preferably with sed.
Thanks in advance.

Like this, but producing the proper number of *'s:
Code:
sed "s/\(.\{3\}\).*/\1*****/"

Input:
Code:
abababab
cdcdcdcdcd
efefefefe

Output:
Code:
aba*****
cdc*******
efe******

# 2  
Try
Code:
sed -E 's/(...)./\1*/; :A s/[*][^*]/**/; tA' file2
aba*****
cdc*******
efe******

For legibility I've used the -E (= -r) option so the parentheses etc. don't need to be escaped.
These 2 Users Gave Thanks to RudiC For This Post:
# 3  
Try:
Code:
sed -e :a -e 's/\(...\)[^*]/\1*/;ta' file

GNU sed:
Code:
sed ':a;s/\(...\)[^*]/\1*/;ta' file

--
Can it be perl?
Code:
perl -pe 's/(?<=...)./*/g' file


Last edited by Scrutinizer; 02-11-2015 at 12:33 AM..
These 2 Users Gave Thanks to Scrutinizer For This Post:
# 4  
Quote:
Originally Posted by RudiC
Try
Code:
sed -E 's/(...)./\1*/; :A s/[*][^*]/**/; tA' file2

Thanks. Although this works fine for the case I presented, I noticed that there could be an issue if one of the first 3 characters was a * to begin with.

In:
Code:
a*a*a*a*

Out:
Code:
a*******

Quote:
Originally Posted by Scrutinizer
Try:
Code:
sed -e :a -e 's/\(...\)[^*]/\1*/;ta' file

GNU/BSD sed:
Code:
sed ':a;s/\(...\)[^*]/\1*/;ta' file

Thanks! These appear to work just fine.
# 5  
Not as nice, but might be easier to maintain:
Code:
while read line
do
	len=${#line}
	[ $len -gt 3 ] && len=$(( $len - 3))
	tmp="$(printf '%*s' $len|sed s,\ ,*,g)"
	echo "${line:0:3}${tmp}"
done<file1

Code:
$ cat file1
abababab
cdcdcdcdcd
efefefefe
a*bcdef

$ bash leolson
aba*****
cdc*******
efe******
a*b****

hth

Last edited by sea; 02-09-2015 at 05:23 PM.. Reason: typo, thx scrutinizer
# 6  
@sea: note that ${line:0:3} is bash syntax (or ksh93 or zsh), so the script should be called with bash, rather than sh. Even though on some systems sh is a link to bash, which will result in calling bash with the --posix option, there are many systems where this is not the case and so there the script would fail if called this way.
This User Gave Thanks to Scrutinizer For This Post:
# 7  
Longhand using OSX 10.7.5, default bash terminal...
Hard coded as '3' for this DEMO.
Code:
Last login: Mon Feb  9 22:00:29 on ttys000
AMIGA:barrywalker~> echo 'kajhd(*&&#$%^ASDFGHJ{}][!\\|\00
> 123131,.,xv.,c.,.?><lksdlfk
> abcd
> def
> a' > /tmp/txt
AMIGA:barrywalker~> while read -r line; do pad="${line:3}"; echo $line; echo -E "${line:0:3}${pad//[' '-~]/*}"; done < /tmp/txt
kajhd(*&&#$%^ASDFGHJ{}][!\\|\00
kaj****************************
123131,.,xv.,c.,.?><lksdlfk
123************************
abcd
abc*
def
def
a
a
AMIGA:barrywalker~> _

EDIT:
Post the correct copy and paste... ;o)

Last edited by wisecracker; 02-09-2015 at 07:21 PM.. Reason: See above.
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