topic Re: shell issue: parameter substitution in Operating System - Linux

shell issue: parameter substitution

Jdamian — Wed, 26 Sep 2007 03:03:41 GMT

Hi

I'm using the ${#} to check lexicographycally an IP address:

IP=192.112
echo "${IP%+([0-9].+([0-9])}"
19

Why does the pattern +([0-9]) remove just ONE digit from the first number while those same pattern removes all digits from the second number ?

Re: shell issue: parameter substitution

TY 007 — Wed, 26 Sep 2007 03:28:34 GMT

Hello Oscar,

Tested in a HP-UX 11.11 OS:

# echo $SHELL
/sbin/sh

# IP=192.112

# echo "${IP%+([0-9].+([0-9])}"
192.112

Thanks

Re: shell issue: parameter substitution

J. Bravo — Wed, 26 Sep 2007 03:32:54 GMT

In my 11.23 box it's working fine with POSIX shell:

# IP=192.112
# echo "${IP%+([0-9].+([0-9])}"
192.112

Best regards.

Re: shell issue: parameter substitution

TY 007 — Wed, 26 Sep 2007 04:01:39 GMT

Hello Oscar,

Tested as well in HP-UX 11.00 OS.

# uname -r
B.11.00

# echo $SHELL
/sbin/sh

# IP=192.112

# echo "${IP%+([0-9].+([0-9])}"
192.112

Thanks

Re: shell issue: parameter substitution

Jdamian — Wed, 26 Sep 2007 04:24:21 GMT

I'm sorry but my patter posted here has a missing character ')', i.e., it's wrong.

Try this next one:

echo "${IP%+([0-9]).+([0-9])}"

Re: shell issue: parameter substitution

AwadheshPandey — Wed, 26 Sep 2007 04:35:05 GMT

Oscar!!

Can you clear what actually you want to print?
Regards,

Awadhesh

Re: shell issue: parameter substitution

Pete Randall — Wed, 26 Sep 2007 05:10:14 GMT

# IP=192.112
# echo "${IP%+([0-9]).+([0-9])}"
19
# uname -r
B.11.11

Pete

Re: shell issue: parameter substitution

TY 007 — Wed, 26 Sep 2007 05:42:53 GMT

Hello Oscar,

# IP=192.112

# AA=`echo $IP | awk -F. '{print $1}'`

# echo "${AA%+([0-9])}"
19

Thanks

Re: shell issue: parameter substitution

TY 007 — Wed, 26 Sep 2007 05:44:32 GMT

Hello Oscar,

# IP=192.112

# BB=`echo $IP | awk -F. '{print $2}'`

# echo "${BB%+([0-9])}"
11

Thanks

Re: shell issue: parameter substitution

James R. Ferguson — Wed, 26 Sep 2007 06:48:25 GMT

Hi Oscar:

# echo "${IP%\.*}"
192

# echo "${IP##[0-9]*\.}"
112

You should escape the dot which otherwise means any character.

Regards!

...JRF...

Re: shell issue: parameter substitution

AwadheshPandey — Wed, 26 Sep 2007 06:56:47 GMT

http://wwwhome.cs.utwente.nl/~broekjg/bsc/scripts/phase2.txt

Re: shell issue: parameter substitution

Sandman! — Wed, 26 Sep 2007 11:00:48 GMT

# echo "${IP%+([0-9]).+([0-9])}"

In the above expression the shell is doing what it has been asked of; delete the shortest matching pattern as a single percent sign was specified. On the other hand if the expression was:

# echo "${IP%%+([0-9]).+([0-9])}"

...then it deletes the longest matching pattern which is the entire string as a double percent sign was specified. See the sh-posix(1) man page for details.

~cheers

Re: shell issue: parameter substitution

Dennis Handly — Thu, 27 Sep 2007 04:38:13 GMT

>JRF: You should escape the dot which otherwise means any character.

Actually no. This is a file matching pattern not a regular expression. In a pattern you have "*" and "?".

Re: shell issue: parameter substitution

Jdamian — Thu, 27 Sep 2007 05:32:20 GMT

Some explanations:

I'm trying to check lexicographically an IP address.

I'm very distrustful :-( -- I don't trust external commands as grep or awk, so I prefer to use shell internal tricks

I know the difference of ${%} and ${%%} but in my example pattern

echo "${IP%+([0-9]).+([0-9])}"

I cannot understand why the same sub-pattern

+([0-9])

matches the full last byte (112) BUT only one digit from the first byte (192).

Does the 'shortest length' behaviour of ${%} apply only to the sub-pattern following the character '%' ?

Thanx in advance

Re: shell issue: parameter substitution

Dennis Handly — Thu, 27 Sep 2007 05:51:49 GMT

>BUT only one digit from the first byte (192).
>Does the 'shortest length' behaviour of ${%} apply only to the sub-pattern following the character '%'?

As Sandman said, it applies to everything. Since the last pattern must match ALL of 112 to match the ".", it does. But to match 192, it only has to match the shortest.

I would suggest you trust in the grep and regular expressions. grep/awk aren't the darkside ;-)

Re: shell issue: parameter substitution

Sandman! — Thu, 27 Sep 2007 09:45:04 GMT

>Does the 'shortest length' behaviour of ${%} apply only to the sub-pattern
>following the character '%' ?

Yes it does...and the difference can be seen in the following constructs...

# IP=192.112
# echo "${IP%+([0-9])}"
192.11
# echo "${IP%%+([0-9])}"
192.

Re: shell issue: parameter substitution

Jdamian — Fri, 28 Sep 2007 04:03:02 GMT

thanx