How to replace commas with white spaces in a csv, but inserting a different number of space after each column

Something like:

sed '/^[[:blank:]]*B$/{n;s/Hello/Hi/g;}'

That assumes there are no consecutive Bs (one B line followed by another B line).

Otherwise, you could do:

awk 'last ~ /^[[:blank:]]*B$/ {gsub("Hello", "Hi")}; {print; last=$0}'

The sed equivalent would be:

sed 'x;/^[[:blank:]]*B$/{
       g;s/Hello/Hi/;b
     }
     g'

To replace the second word after B, or to replace world with universe only if two lines above contained B:

awk 'l2 ~ /B/ {gsub("world","universe")}; {print; l2=l1; l1=$0}'

To generalise it to n lines above:

awk -v n=12 'l[NR%n] ~ /B/ {gsub("foo", "bar")}; {print; l[NR%n]=$0}'

You need to set the field separator (FS) properly. By default, awk uses any horizontal whitespace(s) as the field separator, so in your case SAMS becomes one field and CLUB becomes another. Hence, {gsub("SAMS CLUB","SAM\'S CLUB",$3);print} is not working expectedly.

You can do:

awk -F ', +' '{gsub("SAMS CLUB","SAM'\''S CLUB",$3); print}' OFS=", " file.txt

• -F ', +' sets FS as comma, followed by one or more space(s). If you are unsure about the spaces, use character class [:blank:] instead to represent any horizontal whitespace and change OFS to meet your need as well.

Example:

% cat file.txt                                                                      
column1, coluumn2, coulumn3, column4, column5
1, item1, WALMART, 2.39, 50
2, item2, TARGET, 4.99, 52
3, item3, SAMS CLUB, 8.19, 15
4, item4, KROGER, 12.49, 33
5, item6, WEGMANS, 32.69, 75
6, item6, TARGET, 12.99, 25
7, item7, SAMS CLUB, 8.19, 92

% awk -F ',[[:blank:]]+' '{gsub("SAMS CLUB","SAM'\''S CLUB",$3); print}' OFS=", " file.txt
column1, coluumn2, coulumn3, column4, column5
1, item1, WALMART, 2.39, 50
2, item2, TARGET, 4.99, 52
3, item3, SAM'S CLUB, 8.19, 15
4, item4, KROGER, 12.49, 33
5, item6, WEGMANS, 32.69, 75
6, item6, TARGET, 12.99, 25
7, item7, SAM'S CLUB, 8.19, 92