You need to extract certain parts (fields) of a line (record) and update them.
In the simple case, you want to extract a single field from a line, then perform some operation on it.
For the more complicated case, you need to modify a field in a data file without extracting it. If it’s a simple search and replace, use sed.
For example, let’s switch everyone from csh to sh on this NetBSD system.
|
1 2 3 4 5 |
$ grep csh /etc/passwd root:*:0:0:Charlie &:/root:/bin/csh $ sed 's/csh$/sh/' /etc/passwd | grep '^root' root:*:0:0:Charlie &:/root:/bin/sh |
You can use awk if you need to do arithmetic on a field or modify a string only in a certain field:
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 |
$ cat data_file Line 1 ends Line 2 ends Line 3 ends Line 4 ends Line 5 ends $ awk '{print $1, $2+5, $3}' data_file Line 6 ends Line 7 ends Line 8 ends Line 9 ends Line 10 ends # If the second field contains '3', change it to '8' and mark it $ awk '{ if ($2 == "3") print $1, $2+5, $3, "Tweaked" ; else print $0; }' data_file Line 1 ends Line 2 ends Line 8 ends Tweaked Line 4 ends Line 5 ends |
The possibilities here are as endless as your data, but hopefully the examples above will give you enough of a start to easily modify your data.
