UNIX for Dummies Questions & Answers

Because there is at least a single space before and after the second column in the input file. As I said, it is a rather strange example, since using a single space before and after, like you did, is actually more restrictive than using zero or more spaces, since zero spaces would then also match (for example foo$1234.00bar) , so it serves no purpose whatsoever it might as well be left out.. Further it seems puzzling why there should be a strict match for two (or more) decimals. Also the trailing semi-colon after the print statements is unnecessary and the result could also be accomplished in a rather simpler way.

---edit---

Ah, now I see what you mean:

Code:

/ *\$[1-9][0-9] \.[0-9][0-9] */ { print $1,$2,$3,"*"; }

Yes that is different entirely, since that means there should be a singles space before the dot, so that would not match anything,

whereas previously there was asterisk instead of the space:

Code:

/ *\$[1-9][0-9]*\.[0-9][0-9] */ { print $1,$2,$3,"*"; }

so that meant zero or more digits ([0-9])...

Hi Scrutinizer,

you said

Code:

* means a match for zero or more occurrences of the preceding single character or sub-expression.

then you quote

Code:

Yes that is different entirely, since that means there should be a singles space before the dot, so that would not match anything,
/ *\$[1-9][0-9]\.[0-9][0-9] */

so if i introduce space before decimal in my input file then o/p must be change.
below is my change input file. i have added space before decimal.

Code:

Fruit Price/lbs Quantity
Banana $0.89 100
Peach $0.79 65
Kiwi $1 .50 22
Pineapple $1 .29 35
Apple $0.99 78

so, now as per you the o/p of

Code:

/ *\$[1-9][0-9]\.[0-9][0-9] */

must match with the O/p of

Code:

/ *\$[1-9][0-9]*\.[0-9][0-9] */

.

where the input file for this is

Code:

*\$[1-9][0-9]*\.[0-9][0-9] */

mentioned as below

Code:

Fruit Price/lbs Quantity
Banana $0.89 100
Peach $0.79 65
Kiwi $1 .50 22
Pineapple $1 .29 35
Apple $0.99 78

however, o/p is not the same . can you pls explain this behavior.

alsocan you please explain be what is the significanse or working of each astic in below line. for me it is behaving differently.

Code:

/ *\$[1-9][0-9]*\.[0-9][0-9] */

You are misquoting me. I did not write that regex

Nope. Those are different regexes with different outcomes. The first matches 2 digits before the dot, the second matches one or more digits, in both cases the first digit should be between 1 and 9.
* zero or more spaces
[0-9]* zero or more digits
* zero or more spaces