Shell Programming and Scripting

may i know how can I specify field seperator as comma? (or other sign like $, . and etc)?

use FS for input field separator and OFS for out put field separator, to set what you want as your field separator

Hi jean-pier,

Can you please tell me why we need put 1 after this awk code ?
awk 'NR==2{print "200 300";next}1'

awk ' { BEGIN { FS=","};if (NR == 2) { $2 = 777 ;$1 = 888 }; BEGIN { FS=" "};if (NR == 3) { $3 = 555 } print } ' filename

may i know whether the above syntax correctly defined the fiels seperator or not?
I want to define field seperator twice

You dont need to define field seperator twice.

Code:

awk ' BEGIN { FS=","} { if (NR == 2) { $2 = 777 ;$1 = 888 }; if (NR == 3) { $3 = 555 } print } ' filename

or

Code:

awk -F"," ' { if (NR == 2) { $2 = 777 ;$1 = 888 }; if (NR == 3) { $3 = 555 } print } ' filename

i field seperators that I want in line 2 and line 3 are different. In this case, I need to define field seperator twice, don`t I?

Code:

awk ' BEGIN { FS=","} { if (NR == 2) { $2 = 777 ;$1 = 888 }; if (NR == 3) { FS=" "; $3 = 555 } print } ' filename

after issuing
awk ' BEGIN { FS=","} { if (NR == 2) { $2 = 777 ;$1 = 888 } print } ' filename
command, I found that the line that I edited seperator become a blank. How can I set it back to comma?
For example,
123,456,789 becomes 888 777 789
[what I want is 888,777,789]

one more question, may I know whether filename > filename at the end of awk command is valid or not? I tried to do it but in the end I got a blank file for the original file.