Question

Bash trim and :?

Asked by: Kocil

Dear BASH guru.

I have two simple questions.

1. How to trim a string
e.g:
I have "             aaaaa"    ---->       I want "aaaaa"
I have  "bbbbb          "    ----->     I want "bbbbb"

2. How can I shorten this expression:
if [ $test = 0 ]; then
   VALUE="TRUE"
else
   VALUE="FALSE"
fi

I expect someting like C, eg:
VALUE=(test==0) ? "TRUE" : "FALSE".
Is there similar operator in bash ?

Thanks

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Asked On
2004-06-30 at 23:18:12ID21044340
Tags

bash

,

trim

Topic

Linux Programming

Participating Experts
2
Points
100
Comments
19

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Answers

 

by: sunnycoderPosted on 2004-06-30 at 23:19:49ID: 11443843

Hi Kocil,

> 1. How to trim a string
> e.g:
> I have "             aaaaa"    ---->       I want "aaaaa"
> I have  "bbbbb          "    ----->     I want "bbbbb"

echo $var | sed 's/ //g'
 
> 2. How can I shorten this expression:
> if [ $test = 0 ]; then
>    VALUE="TRUE"
> else
>    VALUE="FALSE"
> fi
>
> I expect someting like C, eg:
> VALUE=(test==0) ? "TRUE" : "FALSE".
> Is there similar operator in bash ?

I dont think you have ? : available on bash

Sunnycoder

 

by: KocilPosted on 2004-06-30 at 23:20:37ID: 11443849

Addition.
The trim should work for multi words.
e.g:
"     aaaa  bbbb"        ===> "aaaa bbbb"
"cccc dddd      "        ===> "cccc dddd"

 

by: sunnycoderPosted on 2004-06-30 at 23:22:15ID: 11443863

Kocil,
> "     aaaa  bbbb"        ===> "aaaa bbbb"
> "cccc dddd      "        ===> "cccc dddd"

do you want only spaces at beginning and end removed or you want spaces between the words trimmed too ?

Sunnycoder

 

by: KocilPosted on 2004-06-30 at 23:28:16ID: 11443898

Hi Sunny.

WOW ... under 1 minute ??? So quick.
I want only spaces at the beginning or the end. Not between the words.

I read the "man bash". I saw there is a ?: operator.
But I can not find the example,  and so far I can only make syntax error. :-)

 

by: sunnycoderPosted on 2004-06-30 at 23:30:06ID: 11443910

1. sed 's/^ *\(.*\) *$/\1/'

2. Let me check again

 

by: KocilPosted on 2004-06-30 at 23:34:38ID: 11443934

Hmm ...
tux@vector:$ echo "  aaaa   bbbb" | sed 's/^ *\(.*\)*$/\1/'
Segmentation fault

LOL :)
Do we find a bug ???

 

by: KocilPosted on 2004-06-30 at 23:38:57ID: 11443951

This is nearly right, but the first character is lost.

tux@vector:$ echo "  aaaa   bbbb" | sed 's/^ *[a-z]//'          
aaa   bbbb

 

by: sunnycoderPosted on 2004-06-30 at 23:40:41ID: 11443962

(( t = a<45?7:11 )) # C&#8722;style trinary operator.

 

by: sunnycoderPosted on 2004-06-30 at 23:55:47ID: 11444054

>tux@vector:$ echo "  aaaa   bbbb" | sed 's/^ *\(.*\)*$/\1/'
>Segmentation fault

you missed the space before *

sed 's/^ *\(.*\) *$/\1/'
                       ^

 

by: sunnycoderPosted on 2004-06-30 at 23:56:33ID: 11444059

The ternary operator has to be used in double parenthesis (( ))

 

by: KocilPosted on 2004-07-01 at 00:00:45ID: 11444081

Yes... it works.

tux@vector:$ echo "  aaaa   bbbb" | sed 's/^ *\(.*\) *$/\1/'
aaaa   bbbb

But how about trim-end ?
tux@vector:$ a=$(echo "  aaaa   bbbb   " | sed 's/^ *\(.*\) *$/\1/')
~
tux@vector:$ echo -$a-
-aaaa bbbb -
~

 

by: sunnycoderPosted on 2004-07-01 at 00:02:47ID: 11444092

it trims the end too (the trailing spaces)

 

by: KocilPosted on 2004-07-01 at 00:06:38ID: 11444119

>>  (( t = a<45?7:11 ))

OK. I missed the (( )).
And more over, it works for number only, doesn't it ?


 

by: KocilPosted on 2004-07-01 at 00:09:10ID: 11444133

There is a space ' ' left in the end.

 

by: sunnycoderPosted on 2004-07-01 at 00:11:02ID: 11444144

is it a space or newline ?

 

by: leflonPosted on 2004-07-01 at 00:11:16ID: 11444147

>> it trims the end too (the trailing spaces)
but in
   sed 's/^ *\(.*\) *$/\1/'
                --------
the
*\(.*\) is greedy and will match any char up to the end (including any trailing blanks/ws). or am i wrong?
so maybe you have to first remove the leading spaces and in a second step the trailing ones? will try as soon as my linux box is up (and i hab a cup of mrning coffee)

leflon

 

by: sunnycoderPosted on 2004-07-01 at 00:15:54ID: 11444176

right. ...

 echo -n "  aaaa   bbbb    " | sed 's/^ *\(.*\)/\1/' | sed 's/ *$//' && echo c

 

by: KocilPosted on 2004-07-01 at 00:18:40ID: 11444188

Ok.

Well, so much for trim :)

Thanks Sunny.

 

by: leflonPosted on 2004-07-01 at 00:26:23ID: 11444228

yep, i have it a bit shorter :-)

echo -n "  aaaa   bbbb    " | sed 's/^ *//' | sed 's/ *$//' && echo c

cheers
leflon

20120131-EE-VQP-002

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