awk and regex with {}

Question

I want to print whole record if it contain word and some character, which are optional. Script:

/mount[ein]{0,2}/{
print $0}

Unfortunately it doesn't work. Without "{" and "}" it work. I tried with "\" befor "{":

/mount[ein]\{0,2\}/{
    print $0}

Other example. For file:

mountx
mounte
mountee
mounteee

Awk:

awk '/mount[ein]{0,2}$/' file

And result:

//nothing

System: Debian 7.8 Linux ibm 3.2.0-4-amd64 #1 SMP Debian 3.2.68-1+deb7u1 x86_64 GNU/Linux

Answer 1

Your regular expression works with both a POSIX compliant awk and GNU awk.

Given the fact the the characters e, i, and n must be present from zero to three times but that there is no further constraint, this part can be removed from the pattern as mount followed by anything or nothing does match anyway. The action (print $0) being also the default one need not to be specified.

Your command can then be simplified to:

awk '/mount/'

Should you want the range to be used, you need to specify something after it, here is an example:

$ cat input
foo
mountx
mounte
mountee
mounteee
$ /usr/xpg4/bin/awk '/mount[ein]{0,2}$/' input
mounte
mountee

That is on Solaris where the POSIX awk is in /usr/xpg4/bin.

Same behavior on the Debian based Mint 17.1:

$ awk -V | head -1      
GNU Awk 4.0.1
$ awk '/mount[ein]{1,2}$/' input     
mounte
mountee

However, it looks like mawk, which claims POSIX compliance, doesn't support the interval (brace) expression.

$ mawk -W version
mawk 1.3.3 Nov 1996, Copyright (C) Michael D. Brennan
$ mawk '/mount[ein]{1,2}$/' input
$ 

This is a known bug.

Answer 2

Example tst.txt:

mountx
mounte
mountee
mounteee

awk (GNU Awk 3.1.7) script

awk --re-interval '/mount[ein]{0,2}$/' tst.txt > tst1.txt

result

mounte
mountee

man awk

-W re-interval
--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  pro-
          vides them if they are requested with this option, or when --posix is specified.

Answer 3

Not sure about your mount command format, and the question is listed as a "awk" question, with no awk in your comment.

Is this what you're looking for?

"print all lines that contain a 0" (or whatever string you're searching for) from a file - use the command

cat temp.txt | grep 0 | awk '{print $0}'

will result in

0 9 8 7 6 5 4 3 2

5 4 3 2 1 0 9 8

where temp.txt is

1 2 3 4 5 6 7

0 9 8 7 6 5 4 3 2

9 8 7 6 5 4

8 7 6 5 4 3

7 6 5 4 3

6 5 4 3

5 4 3 2 1 0 9 8

4

3

2