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Help with bash script.

Posted on 1999-01-03
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Last Modified: 2013-12-26
If I use the program cda I can do a:
cda -dev /dev/cdrom on
cda -dev /dev/cdrom toc

and get the output:

Disc ID: rock 910f850b
Ulf Lundell / Maria Kom Tillbaka - Live - Cd 3

 01 05:59  Laglvs
 02 05:48  Evangeline
 03 04:41  Rom i regnet
 04 05:28  Ute pe vdgen igen
 05 06:30  Dansa nu
 06 04:58  Oh la la
 07 07:24  67
 08 03:17  Min vandrande vdn
 09 10:43  Isabella
 10 06:13  Leng vdg hem
 11 05:12  Maria kom tilllbaka

Total Time: 66:15

How can I make a script that take the trac-names and put them into variabels.
I mean that the variable track01 shall be laglvs and track11 Maria kom tillbaka.

How can I solve this in bash?
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Question by:n94magho
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4 Comments
 

Accepted Solution

by:
hollandb earned 1400 total points
ID: 1295098
I have created a bash script that uses one external program: 'expr', the rest is totally bash.  Note that the variables only exist for the process (child) - they are lost when the script ends hence the parent does not have access to the variables.

This script reads from ./track_titles.txt, but will read from standard input be default if the filename is removed.

It reads a whole line at a time and breaks it up into three variables (track_num, track_time, track_title) using the space as a separator.  If there are more than two spaces, the rest of the line is automatically put into the third variable, in this case 'track_title'.  It then checks to see if the length of the track_num is two(2) characters.  If it is not, it ignores the whole line and continues with the next line.  If it is, it assigns 'trackXX=<track title>' and exports the variable.  I have issued a set command at the end of the script to prove that variables are actually exported.

<START OF SCRIPT:>
#
# Allow input of track names and extract and print them.
#

while read track_num track_time track_title
do
        if [ `expr length "$track_num"` -eq 2 ]
        then
                echo $track_num $track_title;
                export track$track_num=$track_title
        fi
done < './track_titles.txt'

set
<END OF SCRIPT>
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Author Comment

by:n94magho
ID: 1295099
Thanks!
0
 

Author Comment

by:n94magho
ID: 1295100
Hmmmmm.... one comment...

How can I print the trackXX variables so I ven se that they hold the right value.... It seems to me that soemthing is wrong.
0
 

Expert Comment

by:hollandb
ID: 1295101
I have played around with this a bit more and I think you will be happy with what I have come up with.
I have changed the script quite considerably and it doesn't use "expr", instead it uses a built in feature of bash to determine the length of a variable/array.  The code should be self-explanatory:

<START OF SCRIPT:>
#
# Allow input of track names and extract and print them.
#

# declare an array called 'titles':
declare -a titles;
declare -i index=1;

while read track_num track_time track_title
do
        # ${#VAR} uses the builtin capabilities of bash
        # to determine "the length of 'VAR'":
        if [ ${#track_num} -eq 2 ]
        then
                titles[$index]=$track_title;
                let index=$index+1;
        fi
done < './track_titles.txt'

# titles[@] means "the whole array";
# ${#titles[@]} means "the number of elements in the array".
# in this case, index = number of tracks.
index=${#titles[@]};

# print song titles backwards to prove they can be accessed
# by using the appropriate subscript:
while [ $index -gt 0 ]
do
        echo track$index=${titles[$index]};
        let index=$index-1;
done
<END OF SCRIPT>

Regards,
Brian.
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