Classic Shell Scripting

One-Line Programs in awk

We have now covered enough awk to do useful things with as little as one line of code; few other programming languages can do so much with so little. In this section, we present some examples of these one-liners, although page-width limitations sometimes force us to wrap them onto more than one line. In some of the examples, we show multiple ways to program a solution in awk, or with other Unix tools:

• We start with a simple implementation in awk of the Unix word-count utility, wc:

awk '{ C += length($0) + 1; W += NF } END { print NR, W, C }'

• Notice that pattern/action groups need not be separated by newlines, even though we usually do that for readability. Although we could have included an initialization block of the form BEGIN { C = W = 0 }, awk's guaranteed default initializations make it unnecessary. The character count in C is updated at each record to count the record length, plus the newline that is the default record separator. The word count in W accumulates the number of fields. We do not need to keep a line-count variable because the built-in record count, NR, automatically tracks that information for us. The END action handles the printing of the one-line report that wc produces.

• awk exits immediately without reading any input if its program is empty, so it can match cat as an efficient data sink:

$ time cat *.xml > /dev/null
0.035u 0.121s 0:00.21 71.4%     0+0k 0+0io 99pf+0w
$ time awk '' *.xml
0.136u 0.051s 0:00.21 85.7%     0+0k 0+0io 140pf+0w

• Apart ...