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Old 03-01-2011, 08:19 AM   #1
rrije
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bash: regexp in 'if' doesn't evaluate correctly


Hi,

I'm using an 'if' statement to check whether one of positional arguments is a word or a construction like "x-y", but something doesn't seem right.

Here is the relevant part of the code:
Code:
if [[ "$3" =~ [a-Z]\-[a-Z] || "$3" =~ [a-Z] ]]; then 
grepRange=$3; else grepRange=$4
fi
And for the input like this:
Code:
bash -x script --list free fornax
it outputs this:
Code:
+ [[ fornax =~ [a-Z]-[a-Z] ]]
+ [[ fornax =~ [a-Z] ]]
+ grepRange=fornax
but shouldn't the $grepRange variable be blank in this case?

Bash version is 4.1.7(1)

Is there something I'm missing? Enclosing regexp in quotes or double quotes doesn't help.

Thanks in advance.
 
Old 03-01-2011, 08:23 AM   #2
colucix
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Nope. The second regexp is matched:
Code:
[[ fornax =~ [a-Z] ]]
so that according to your code grepRange is $3. Please, can you better explain what you're trying to achieve?
 
Old 03-01-2011, 08:44 AM   #3
rrije
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Thanks!

I've adjusted it to ^[a-Z]$ and it works okay.

The script itself cats a file and breaks the list down into sections according to the first letter of a line.
 
Old 03-01-2011, 09:28 AM   #4
grail
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If only interested in the first letter, why not use that as the test:
Code:
if [[ ${3:0:1} =~ [a-Z] ]] ...
 
Old 03-01-2011, 10:52 AM   #5
crts
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Quote:
Originally Posted by grail View Post
If only interested in the first letter, why not use that as the test:
Code:
if [[ ${3:0:1} =~ [a-Z] ]] ...
If I understood the OP correctly then he only wants the branch to execute if $3 consists of one single letter.

@OP: You probably can also use this RegEx for both your cases:
Code:
if [[ "$3" =~ ^[a-Z](-[a-Z])?$ ]];then
and get rid of the extra OR comparison. Works with my bash version 4.1.5.
 
Old 03-01-2011, 01:44 PM   #6
rrije
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Thanks for the replies everyone.

Allow me to elaborate a bit on a purpose of the script:
There is a plaintext file containing a number of entries (several files, actually); I need to be able to list these entries by filename (or everything at once) and by letter (or several letters).

Here is a part of the code (screenshot, for syntax highlighting) and exemple output; it's a mess, but as a beginner I figured you have to start somewhere. I'd be grateful for any tips you could give.
 
Old 03-02-2011, 12:45 AM   #7
grail
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Well on a cursory look, my main thought is:

Try to look at the places where you have multiple pipes, especially when it is multiple pipes to / through the same application:
Code:
ls ... | grep ... | grep ... | sed ... | xargs ... | grep ... | sort ...
I would guarantee this could lose at least 3 of the pipes if not more with a little investigation.
 
  


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