Shell Programming and Scripting

Hi all,

i have a text file something like that

FLAG DATE(YYYYMMDD) TIME(HHMMSS)

FLAG1 DATE20060101 141216
FLAG1 DATE20070101 141216
FLAG2 DATE20060102 140010
FLAG2 DATE20060103 101212
FLAG1 DATE20070101 101111


using sed, i want to change some of these dates depending on their flag

for example i want to change all FLAG1 dates to a constant date
like DATE20081201
how can i achieve this?
(i am really weak on regular expressions)

Code:

sed -e "s_FLAG1_DATE20081201_g" in > out

thanks for the reply,
but when i run sed as you described i got this output

DATE20081201 DATE20060101 141216
DATE20081201 DATE20070101 141216
FLAG2 DATE20060102 140010
FLAG2 DATE20060103 101212
DATE20081201 DATE20070101 101111

that is not what i want,
i want the out like the one below:

FLAG DATE(YYYYMMDD) TIME(HHMMSS)

FLAG1 DATE20081201 141216
FLAG1 DATE20081201 141216
FLAG2 DATE20060102 140010
FLAG2 DATE20060103 101212
FLAG1 DATE20081201 101111


and what is that syntax : "s_FLAG1_DATE20081201_g"
can u explain a little bit?

try this,

Code:

awk -F" " '{ if ( $1 !~ /FLAG1/ ) { print } else { print $1" ""DATE20081201"" "$3 } }' inputfile

thank you very much matrixmadhan for this awk answer,
a little bit explanation about your usage of awk in that line will
be very appreciated.
i am confused about that braces and double quotation marks.

you are welcome
break it .... everything would become simpler
here it is

Code:

awk -F" " '{ if ( $1 !~ /FLAG1/ ) { print } else { print $1" ""DATE20081201"" "$3 } }' inputfile

Delimiter between fields is space

check for the first field in the line if it is not FLAG1 we can print everything as it is - just use print
if the first field in the line is FLAG1 then just print the first field (FLAG1), followed by a space denoted by " " and the constant date field and space again " " and the third field as such..

everything is really very clear now,
thank you again matrixmadhan