Simple trouble with awk and regex

Question

 echo xx y11y rrr | awk '{ if ($2 ~/y[1-5]{2}y/) print $3}'

Why I cannot get any output?

Thank you.

What output are you expecting? – jsalonen Dec 01 '11 at 14:39 — jsalonen, Dec 01 '11 at 14:39

score 10 · Accepted Answer · answered Dec 01 '11 at 14:46

10

You need to enable "interval expressions" in regular expression matching by specifying either the --posix or --re-interval option.

e.g.

echo xx y11y rrr | awk --re-interval '{ if ($2 ~ /y[1-5]{2}y/) print $3}

From the man page:

--re-interval Enable the use of interval expressions in regular expression matching (see Regular Expressions, below). Interval expressions were not traditionally available in the AWK language. The POSIX standard added them, to make awk and egrep consistent with each other. However, their use is likely to break old AWK programs, so gawk only provides them if they are requested with this option, or when --posix is specified.

answered Dec 01 '11 at 14:46

dogbane

266,786
75
396
414

So what should I do if donot use `{}`expression ? – znlyj Dec 01 '11 at 14:53
instead of `[1-5]{2}`, you can use `[1-5][1-5]`. – dogbane Dec 01 '11 at 14:54
1

nope, interval expressions such as `{2}` won't work unless you use the `--re-interval` or `--posix` flag. – dogbane Dec 01 '11 at 14:57
`echo xx y11y rrr | awk --posix '{ if ($2 ~/y[1-5]\{2\}y/) print $3}' ` . It seems get no output. – znlyj Dec 01 '11 at 15:02
1

you don't need to escape the curly braces. – dogbane Dec 01 '11 at 15:10
2

To make it explicit: this applies to `gawk` (GNU `awk`) only. Quick update: since `gawk 4.0` you no longer need `--re-interval`. – mklement0 May 09 '14 at 03:46

Eric Wilson · Answer 2 · 2011-12-01T14:48:33.583

0

On my machine:

$ echo xx y11y rrr | awk '{ if ($2 ~/y[1-5]{2}y/) print $3}'
rrr

Was this what you wanted? I'm using GNU awk 4.0.0 in Cygwin on Windows XP.

edited Dec 01 '11 at 14:48

answered Dec 01 '11 at 14:41

Eric Wilson

57,719
77
200
270

eh, I still cannot get any output with your answer. – znlyj Dec 01 '11 at 14:42
Seems like OS specific problem – jsalonen Dec 01 '11 at 14:44
1

The need to specify `--re-interval` in order to support interval expressions was dropped in gawk `4.0.0`. – mklement0 May 09 '14 at 11:57

score 0 · Answer 3 · answered Dec 01 '11 at 14:45

0

You should force POSIX to use {} in awk

echo xx y11y rrr | awk -W posix '{ if ($2 ~/y[1-5]{2}y/) print $3}'

answered Dec 01 '11 at 14:45

Ximik

2,435
3
27
53

You try to use POSIX-regexp feature, but awk uses it's own regexp format. So u should force using POSIX format of regexp. Also look at dogbane's answer. – Ximik Dec 01 '11 at 14:51

Simple trouble with awk and regex

3 Answers3

Linked

Related