If you haven't seen awk, then jawk can be described as a flexible tool
for extracting columns of data from text files.
If you've seen 'awk', then we can describe jawk as a replacement for
statements like
awk '{print $N}'
which supports ranges, indexing columns by negative numbers, a perl
mode, and more.
DESCRIPTION
jawk 1 is somewhat like awk '{print $1}'. Let's start with a fairly
complex example. Suppose you have a file called 'users.txt' with lines
of data in this format:
Bob Elmer, 2716 Fremont Blvd, New York, NY, 12344, ID:91818, CanastaRating:3.1415
Elmer Fudd, 1 Bunny Hill Drive, Tarrytown, NY, 87654, ID:1, CanastaRating:123456789
This statement would pull out the 1st, and 3rd through last columns,
using ', ' as an input delimiter (we've put two spaces between options,
for clarity):
jawk -d', ' 1 3..-1 -- users.txt
Note the use of negative indexes, the non-default element delimiter via
`-d', and the `--' anti-option (which indicates that following arguments
should be considered files to read).
jawk also allows ranges using the `..' sequence. For example, a field
specification can look like `A', `A..B', `A..', or `..B', where (`A' and
`B' can be negative or positive integers.
Negative values for A and B count backwards, so -1 is the last field.
Use -- or - FILENAME.txt to read from files. '--' is needed to treat
FILENAME.txt as file and not fieldspec. See examples below.
Where you might previously use a command like
grep pattern file.txt | awk '{print $2}'
to pull out the 2nd column from a file, you can now do:
grep pattern file.txt | jawk 2
jawk offers many other improvements. Here are examples:
select out the 1st, 3rd, and 4th columns from file
cat file | jawk 1 3 4
select all columns except the 1st, and 9th through remaining. Uses the
-x option for an 'except' meaning.
cat file | jawk -x 1 9..-1
select out the first through third, and the second to last, and last
cols from a file.
cat file | jawk 1..3 -2 -1
Same as above, but using : as an input delimiter instead of whitespace.
Note use of -- to start list of files to read from @ARGV, so we can pass
`file' to jawk directly instead of through `cat'.
jawk -d: 1..3 -2 -1 -- file
There is also a -exe='perlcode' mode where you access the args via @F,
and not via named positional args. Like so:
cat file | jawk -e 'print "@F\n";'
OPTIONS
Here's an explation of all the command-line options:
`NON-ZERO INTEGER'
A field specification option indicating that this particular column
should (or should not, depending on -x, be output).
Negative indexes count from the right, like in perl, so the
right-most column is number `-1'.
`RANGE OF NON-ZERO INTEGERS'
Integer ranges are specified with `..', and given that A and B are
non-zero integers, can look like
A..B
A..
..B
If you specify ranges in reverse order from their source, like `cat
file | jawk -1..1' or `cat file | jawk 8-2' you'll get the fields in
reverse order, like you asked.
-d delimiter (or -d=delimiter)
Specify an alternate delimiter in place of '\s+'. If not ' ', the
delimiter is processed through perl's quotemeta() function and used
as a regular expression to match between input fields.
-j joiner (or -j=joiner)
Specify an alternate join character sequence in place of 'space'.
-x Exclude the chosen columns, negating their meaning. Does not
interoperate with -e 'perlcode' option.
-e='perlcode' or -e 'perlcode'
Use perl code passed to process parsed items. Fields come in through
the @F array, and are 0-indexed (like in perl) instead of 1-indexed
(like in jawk and cut). A simple example, which shows the first and
second columns of input, is
cat file.txt | jawk -e 'print "$F[0] $F[1]\n"'
-w Run perl code used with -e option with warnings on. (Strictness is
always enabled but can be disabled by putting 'no strict' in your
script).
-- Ends argument parsing. Used to pass filenames to read from stdin.
See examples above.
BUGS
None known
COPYRIGHT
Copyright (c) 2011 Josh Rabinowitz, All Rights Reserved.
