How to use sed for substituting 2nd column in shell

Question

I have file that looks like this :

1,2,3,4
5,6,7,8

I want to substitute 2rd column containing 6 to 89. The desired output is

1,2,3,4
5,89,7,8

But if I type

index=2
cat file | sed 's/[^,]*/89/'$index

I get

1,89,3,4
5,89,7,8

and if I type

index=2
cat file | sed 's/[^,]6/89/'$index

nothing changes. Why is it like this? How can I fix this? Thank you.

`[^,]` matches a single character which is not comma (or newline). It is unclear what you imagine it should match. — tripleee, Nov 13 '18 at 04:59
Possible duplicate of [How to replace second column of csv file with a specific value "XYX"](https://stackoverflow.com/questions/15745250/how-to-replace-second-column-of-csv-file-with-a-specific-value-xyx) — tripleee, Nov 13 '18 at 04:59
Possible duplicate of https://stackoverflow.com/questions/49833671/sed-replace-nth-column-of-multiple-tsv-files-without-header — tripleee, Nov 13 '18 at 05:05
Yes I did not know what [^,] means. Thank you! I don't need to substitute all lines — wkde, Nov 13 '18 at 06:02

score 2 · Accepted Answer · answered Nov 13 '18 at 11:37

Since you want to change the second column containing a 6 and you have a comma as field separator it is actually very easy with sed:

sed 's/^\([^,]*\),6,/\1,89,/`

Here we make use of back-referencing to remember the first column.

If you want to replace the 6 in the 5th column, you can do something like:

sed 's/^\(\([^,]*,\)\{4\}\)6,/\189,/'

It is, however, much more comfortable using awk:

awk 'BEGIN{FS=OFS=","}($2==6){$2=89}1'

score 0 · Answer 2 · answered Nov 13 '18 at 06:03

0

I solved this by using awk

awk 'BEGIN{FS=OFS=","} {if ($2==6) $2=89}1' file >file1

answered Nov 13 '18 at 06:03

wkde

2 Answers2