Suppose I have a string "123456789".
I want to extract the 3rd, 6th, and 8th element. I guess I can use
cut -3, -6, -8
But if this gives
368
Suppose I want to separate them by a white space to get
3 6 8
What should I do?
4 Answers
Actually shell parameter expansion lets you do substring slicing directly, so you could just do:
x='123456789'
echo "${x:3:1}" "${x:6:1}" "${x:8:1}"
Update
To do this over an entire file, read the line in a loop:
while read x; do
echo "${x:3:1}" "${x:6:1}" "${x:8:1}"
done < file
(By the way, bash slicing is zero-indexed, so if you want the numbers '3', '6' and '8' you'd really want ${x:2:1} ${x:5:1} and {$x:7:1}.)
2 Comments
Smith Black
Thanks for your response. Is it possible to generalize this to extracting the 3rd, 6th, and 8th characters for all lines in a file?
Digital Trauma
Can you try
echo "${x:2:1}" "${x:5:1}" "${x:7:1}" instead? In both bashes (Linux and OSX) I've tested, the character counting is 0-based, not 1-basedYou can use the sed tool and issue this command in your teminal:
sed -r "s/^..(.)..(.).(.).*$/\1 \2 \3/"
Explained RegEx: http://regex101.com/r/fH7zW6
To "generalize" this on a file you can pipe it after a cat like so:
cat file.txt|sed -r "s/^..(.)..(.).(.).*$/\1 \2 \3/"
5 Comments
Smith Black
Thank you for your response. It seems like this part "..(.)..(.).(.)." works when we know the length of the string. If we don't know how many characters in each line (possible very big number), does this still work?
CSᵠ
This works when the line has at least 8 characters as it discards anything else after the 8th so yes, it can very big.
kojiro
No need for a cat. Just redirect the file to sed.
sed … < fileSmith Black
Thank you. Just a follow up question. If I want to extract the 999th character, do I need to put 998 "." followed by "(.)" ?
CSᵠ
no, put
.{998}(.) I used multiple dots (without quantifier) to be simpler, it's equivalent to: /^.{2}(.).{2}(.).(.).*$/Perl one-liner.
perl -lne '@A = split //; print "$A[2] $A[5] $A[7]"' file
Comments
Using cut:
$ cat input
1234567890
2345678901
3456789012
4567890123
5678901234
$ cut -b3,6,8 --output-delimiter=" " input
3 6 8
4 7 9
5 8 0
6 9 1
7 0 2
The -b option selects only the specified bytes. The output delimiter can be specified using --output-delimiter.
cut.echo $SHELLcutcan provide the desired output!