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(gawk.info)Command Line Field Separator

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Setting `FS' from the Command Line
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   `FS' can be set on the command line.  Use the `-F' option to do so.
For example:

     awk -F, 'PROGRAM' INPUT-FILES

sets `FS' to the `,' character.  Notice that the option uses a capital
`F' instead of a lowercase `-f', which specifies a file containing an
`awk' program.  Case is significant in command-line options: the `-F'
and `-f' options have nothing to do with each other.  You can use both
options at the same time to set the `FS' variable _and_ get an `awk'
program from a file.

   The value used for the argument to `-F' is processed in exactly the
same way as assignments to the built-in variable `FS'.  Any special
characters in the field separator must be escaped appropriately.  For
example, to use a `\' as the field separator on the command line, you
would have to type:

     # same as FS = "\\"
     awk -F\\\\ '...' files ...

Because `\' is used for quoting in the shell, `awk' sees `-F\\'.  Then
`awk' processes the `\\' for escape characters (Note: Escape
Sequences), finally yielding a single `\' to use for the field
separator.

   As a special case, in compatibility mode (Note: Command-Line
Options.), if the argument to `-F' is `t', then `FS' is set to
the tab character.  If you type `-F\t' at the shell, without any
quotes, the `\' gets deleted, so `awk' figures that you really want
your fields to be separated with tabs and not `t's.  Use `-v FS="t"' or
`-F"[t]"' on the command line if you really do want to separate your
fields with `t's.

   For example, let's use an `awk' program file called `baud.awk' that
contains the pattern `/300/' and the action `print $1':

     /300/   { print $1 }

   Let's also set `FS' to be the `-' character and run the program on
the file `BBS-list'.  The following command prints a list of the names
of the bulletin boards that operate at 300 baud and the first three
digits of their phone numbers:

     $ awk -F- -f baud.awk BBS-list
     -| aardvark     555
     -| alpo
     -| barfly       555
     -| bites        555
     -| camelot      555
     -| core         555
     -| fooey        555
     -| foot         555
     -| macfoo       555
     -| sdace        555
     -| sabafoo      555

Note the second line of output.  The second line in the original file
looked like this:

     alpo-net     555-3412     2400/1200/300     A

   The `-' as part of the system's name was used as the field
separator, instead of the `-' in the phone number that was originally
intended.  This demonstrates why you have to be careful in choosing
your field and record separators.

   Perhaps the most common use of a single character as the field
separator occurs when processing the Unix system password file.  On
many Unix systems, each user has a separate entry in the system password
file, one line per user.  The information in these lines is separated
by colons.  The first field is the user's logon name and the second is
the user's (encrypted or shadow) password.  A password file entry might
look like this:

     arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/bash

   The following program searches the system password file and prints
the entries for users who have no password:

     awk -F: '$2 == ""' /etc/passwd