This variable is used to set the output field separator which is a space by default.
awk -F'=' 'BEGIN { OFS=":" } { print $1 }' file
Example:
$ cat file.csv
col1,col2,col3,col4
col1,col2,col3
col1,col2
col1
col1,col2,col3,col4,col5
$ awk -F',' 'BEGIN { OFS="|" } { $1=$1 } 1' file.csv
col1|col2|col3|col4
col1|col2|col3
col1|col2
col1
col1|col2|col3|col4|col5
Assigning $1
to $1
in $1=$1
modifies a field ($1
in this case) and that results in awk
rebuilding the record $0
. Rebuilding the record replaces the delimiters FS
with OFS
.