modify field

tostay2003 · 07-29-2008, 04:49 PM

I have a huge pipe delimited file. And I need to modify only the fifth field (apply an if or case statment on it). How can we do that and still having other fields intact.

eg.

Before

File1

Code:

F1|F2|F3|F4|F5

After

File1

Code:

F1|F2|F3|(F4>10? F4-1:F4+1) |F5

Mr. C. · 07-29-2008, 05:13 PM

You can use awk or perl, setting the field separator to '|', and output the first four fields as is, and perform your calculations on field five.

Do all lines have exactly 5 fields?

tostay2003 · 07-29-2008, 05:23 PM

not 5 fields, but say N fields and its the same for all the lines

Mr. C. · 07-29-2008, 05:37 PM

awk -F'|' 'BEGIN {OFS="|"} /\|/ {print $1,$2,$3,$4,$5}' data_file

Now, you change $5 to be what you want.

tostay2003 · 07-29-2008, 06:48 PM

Quote:

awk -F'|' 'BEGIN {OFS="|"} /\|/ {print $1,$2,$3,$4,`expr length $5` > 2 ?:$5}' data_file

I tried to modify the code as above... basically to check if the length of the fifth field is greater than 2, if it is then do nothing else retain the $5 field.

but the expression above gives awk syntax error.

Quote:

awk -F'|' ' -v f8=`expr length $5` BEGIN {OFS="|"} /\|/ {print $1,$2,$3,$4,f8>2?:$5}' data_file

The above statment as well fails due to awk syntax error .

Mr. C. · 07-29-2008, 07:00 PM

Why are you calling expr within awk ? awk is perfectly capable of determining the length of a string.

Here's the GNU awk manual.

http://www.gnu.org/manual/gawk/html_node/index.html

Spend some time actually reading it to learn about awk syntax and commands. I see from your other threads this is an ongoing issue, so its worth your time to learn.

Build one small awk statement at a time; when you get them working individually, then put them together. In the case above, try printing out the length of a string entirely from within awk.

chrism01 · 07-29-2008, 08:27 PM

I note in your example you're actually modifying the 4th field, not the 5th... Or even 3rd field if you're talking offsets...

tostay2003 · 07-31-2008, 03:24 PM

I brushed through awk a bit and went ahead with this code ... but it gives me syntax error. Tried to

Code:

awk -F'|' 'BEGIN {OFS="|"} {if (length($4)>2) $4="" else $4=$4; print $0}' data_file

Mr. C. · 07-31-2008, 07:06 PM

Remove the else $4=$4. Not only is it a no-op ($4 already equals $4 !), but the syntax is incorrect (you'd need a semicolon just before the else.

ghostdog74 · 07-31-2008, 11:51 PM

awk already has an "internal if", so in your case, there's no need for if/else

Code:

awk 'BEGIN{OFS="|";FS="|"}length($4)>2{$4=""}1' file

tostay2003 · 08-01-2008, 11:26 AM

Thanks for the feedback.