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In file data is like below

Sample input:

123,xyz,456,abc

We need add single quotation for all string's only. First need check either number or string, For suppose first one is number not require to add the single quotation after comma next string need add the single quotation marks like below output.

123,'xyz',456,'abc'

echo ,123,xyz,456,,abc2 |
 sed "s/[^,]*[^,0-9][^,]*/'&'/g;s/^,/'',/;s/,$/,''/;:1
 s/,,/,'',/g;t1"
'',123,'xyz',456,'','abc2'

would enclose in quotes any comma-separated field that is not made exclusively of one or more decimal digits (that is empty fields like for lines that start (/^,/) or end (/,$/) with , or contain ,, and fields containing at least one non-digit (/[^,]*[^,0-9][^,]*/)).

If you want to recognise arbitrary decimal floating point numbers like -2, 1.23, 1e-2, that would become more complicated and you may want to resort to awk:

awk -F, -v OFS=, -v q="'" '
 
 for (i = 1; i <= NF; i++)
 if ($i !~ /^[[:blank:]]*[-+]?([0-9]+.?[0-9]*'

That changes:

abc,,0x20, +2.23E-5 , x y ,-2

to:

'abc','','0x20', +2.23E-5 ,' x y ',-2

If you wanted to get

'abc','','0x20', +2.23E-5 , 'x y' ,-2

instead, you'd do:

awk -F, -v OFS=, -v q="'" '
 
 for (i = 1; i <= NF; i++)
 if ($i !~ /^[[:blank:]]*[-+]?([0-9]+.?[0-9]*'

With sed if your input data in each fields are only digits or alpha:

sed -E "s/[[:alpha:]]+/'&'/g" <<<"123,xyz,456,abc"

Or in complex mode.

sed -E "s/[0-9]*[[:alpha:]-]+[0-9]*/'&'/g" infile

Input:

123,xyz,456,abc
abc123,,a-b,5

Output:

123,'xyz',456,'abc'
'abc123',,'a-b',5