Software Salariman: Gawk

Showing posts with label Gawk. Show all posts

2011-02-12

Negate Numbers as String in Gawk

I had to negate numbers in a data file. My initial script simply negated the required field. Here a test:

gawk "{ print -$1 }"
123
-123
123.45678
-123.457

I wanted to preserve all the digits after the decimal point so I tried printf() (the multiple double-quotes is to escape double-quotes in Windows CMD):

gawk "{ printf("""%10lf\n""", -$1) }"
123
-123.000000
123.45678
-123.456780
123.456
-123.456000

Hm, now the result was being padded to the right depending on the number of digits specified. Since I only wanted to negate the values and not do any arithmetic, a trick is to add or delete the leading minus sign from the input string depending whether the input value was positive or negative, respectively:

gawk "{ print $1<0 ? substr($1, 2) : """-""" $1 }"
123
-123
123.45678
-123.45678
-123
123
-123.45678
123.45678

2008-07-28

Extract Lines with Line Numbers using Gawk, Groovy, Perl, Python and Ruby

More ways to extract a block of text from a stream and prepend the line number to each line.

Below is the Gawk version. The built-in variables NR is the number of the current line and $0 is the content of the current line.

gawk "(NR >= r1 && NR <= r2) {printf("""%4d %s\n""", NR, $0)}"

The Perl and Ruby scripts are exactly the same. The built-in variable $. holds the number of the current line and $_ holds the text of the current line.

perl|ruby -ne "printf '%4d %s', $., $_ if $. >= r1 && $. <= r2"

The Groovy command line options are similar to the Perl and Ruby version, except that you have to separate -n and -e. The built-in variable count holds the number of the current line and line holds the text of the current line.

groovy -n -e "if (count >= r1 && count <= r2) out.format '%4d %s\n', count, line"

The Python version is verbose due to boilerplate code to iterate through all rows in a file:

python -c "import sys; print ''.join('%4d %s' % (r, l) for r, l in enumerate(sys.stdin) if r >= r1 and r <= r2)"

PS

2008-07-29: Added Groovy version.

2008-06-24

Gawk Print Last Field

gawk script to print the last field of each line:

gawk -F <delimiter> "{ print $NF }".

-F defines the separator in the command line, otherwise you would prepend "BEGIN { FS=<delimiter> }".

NF is the number of fields in a line and $n is the value of the n'th field, so $NF outputs the last field.

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