I'm trying to learn some basic scripting but I ran into a problem trying to get the number of tracks from the stdout of cdparanoia:
Code:
cdparanoia III release 10.2 (September 11, 2008)
Table of contents (audio tracks only):
track length begin copy pre ch
===========================================================
1. 20769 [04:36.69] 0 [00:00.00] no no 2
2. 11601 [02:34.51] 20769 [04:36.69] no no 2
3. 23132 [05:08.32] 32370 [07:11.45] no no 2
4. 22598 [05:01.23] 55502 [12:20.02] no no 2
5. 19510 [04:20.10] 78100 [17:21.25] no no 2
6. 18957 [04:12.57] 97610 [21:41.35] no no 2
7. 12103 [02:41.28] 116567 [25:54.17] no no 2
8. 25735 [05:43.10] 128670 [28:35.45] no no 2
9. 19409 [04:18.59] 154405 [34:18.55] no no 2
10. 12771 [02:50.21] 173814 [38:37.39] no no 2
11. 16617 [03:41.42] 186585 [41:27.60] no no 2
12. 22036 [04:53.61] 203202 [45:09.27] no no 2
13. 18105 [04:01.30] 225238 [50:03.13] no no 2
14. 11389 [02:31.64] 243343 [54:04.43] no no 2
15. 16964 [03:46.14] 254732 [56:36.32] no no 2
16. 13345 [02:57.70] 271696 [60:22.46] no no 2
17. 22906 [05:05.31] 285041 [63:20.41] no no 2
18. 24715 [05:29.40] 307947 [68:25.72] no no 2
TOTAL 332662 [73:55.37] (audio only)
Now my first thought was it would be nice to get the script to recognize that "18." was the last track in the listing from cdparanoia, but I have no idea how to iterate a search for a number prior to ". ", that is dot-space or dot-space-space where it will successively replace the value of the track number from 1 to 18 (in this example) in a variable, say $END.
Since I didn't know how to do that and it seemed a little complicated I thought how about taking the line number of "TOTAL" and subtracting the number of prefix lines and the "TOTAL" line itself , 8, giving me my 18.
I tried to execute
Code:
cdparanoia -Q | grep -n -o "TOTAL"
and it did not send the output to grep. Why??
So what I'm really looking to do at this point is figure out some way I can make that work. Then my next step is to get the output (in this case 26:TOTAL) and taking the value before the : and subtracting 8 and putting it into $END.
I did see an example that took the cdparanoia output and then used &> to put it in a file...but I don't want to make a temp file if I don't have to.
Once I get that done, I have the basics of the script then I think I would probably like to get a bit more complicated like tacking a +1 on the end of the filename in the /rip directory so I don't have to keep track.
For some odd reason, cdparanoia seems to write to stderr and not stdout and that is why the list didn't go to grep. A simple redirect and pipe to awk and you'll have your answer without having to do any counting, and without depending on the it always writing the same number of header/trailer lines.
Code:
#!/usr/bin/env ksh
cdparanoia -Q 2>&1| awk ' $1+0 > 0 { n=$1+0; next; } END { print n}' |read END
Perhaps I should have mentioned I'm using Ubuntu 10.10 in case that is relevant, and I would prefer to use /bin/bash since that is what most of the examples are in.
Anyway, I take it that "simple redirect" is the 2>&1 to the pipe. I didn't want to use the awk statement because I have no clue what that means and so I would be copying and pasting rather than learning anything. Would you explain what that statement does?
Quote:
Originally Posted by agama
For some odd reason, cdparanoia seems to write to stderr and not stdout and that is why the list didn't go to grep. A simple redirect and pipe to awk and you'll have your answer without having to do any counting, and without depending on the it always writing the same number of header/trailer lines.
Code:
#!/usr/bin/env ksh
cdparanoia -Q 2>&1| awk ' $1+0 > 0 { n=$1+0; next; } END { print n}' |read END
Using bash is perfectly acceptable. Kshell has a few features that make it more attractive to me, but that's a personal preference.
The 2>&1 causes output to stderr (file descriptor 2) to be written onto stdout (file descriptor 1) which is what the shell maps to the process on the other side of the pipe.
Some comments on the awk:
Code:
awk '
$1+0 > 0 { # when the first field converted to a number is greater than 0
n = $1+0; # save the first field as a number in variable n
next; # continue processing with next line of input (not required for this case, but good form)
}
END { # execute this code after the last line of input has been processed
print n; # print the value of n to standard output
}'
In short, awk reads the input file (or from the pipe a.k.a. stdin) and for each line of input executes the programme. In this case the programme is a very simple check to see if the first column (or field if you like that phrase) contains a digit, and if it does the code in curly braces is executed (saving that value in n).
It uses a bit of awk trickiness to do this. The field is added to 0 knowing that awk will convert any text string to 0 and for each record that does not start with a number (e.g. 1.) the result will be 0 + 0 and the condition will be false; the code will not be executed and n will not be changed.
Here's a link to a decent tutorial on awk -- worth the read as awk is one of the (IMHO) most useful tools available to a UNIX programmer.
Using bash is perfectly acceptable. Kshell has a few features that make it more attractive to me, but that's a personal preference.
The 2>&1 causes output to stderr (file descriptor 2) to be written onto stdout (file descriptor 1) which is what the shell maps to the process on the other side of the pipe.
Some comments on the awk:
Code:
awk '
$1+0 > 0 { # when the first field converted to a number is greater than 0
n = $1+0; # save the first field as a number in variable n
next; # continue processing with next line of input (not required for this case, but good form)
}
END { # execute this code after the last line of input has been processed
print n; # print the value of n to standard output
}'
In short, awk reads the input file (or from the pipe a.k.a. stdin) and for each line of input executes the programme. In this case the programme is a very simple check to see if the first column (or field if you like that phrase) contains a digit, and if it does the code in curly braces is executed (saving that value in n).
It uses a bit of awk trickiness to do this. The field is added to 0 knowing that awk will convert any text string to 0 and for each record that does not start with a number (e.g. 1.) the result will be 0 + 0 and the condition will be false; the code will not be executed and n will not be changed.
Here's a link to a decent tutorial on awk -- worth the read as awk is one of the (IMHO) most useful tools available to a UNIX programmer.
You are only allowed to post URLs once you have at least 5 posts.
Hope this helps.
Ok, I think I understand what you're doing with awk, it is just so impenetrable at this point that it doesn't make much sense. I am best at learning by doing so an awk guide makes less sense to me than to tackle it via grep... That said, let me see if I understand your comment about awk, you said first column or field, but in reality, it is just the first character on the line that has to be a number, correct?
Also, I was able to get the right number, but I think your commented code has something wrong with it... I had to make the following modifications:
Code:
#END=$(cdparanoia -Q 2>&1| awk ' $1+0 > 0 { n=$1+0; next; } END { print n}' )
END=$(cdparanoia -Q 2>&1| awk ' $1+0 > 0 { # when the first field converted to a number is greater than 0
n = $1+0; # save the first field as a number in variable n
next; # continue processing with next line of input (not required for this case, but good form)
}
END { # execute this code after the last line of input has been processed
print n}') # print the value of n to standard output
echo $END
So the $1+0 actually adds the initial number on the line? If it was 139ab5, $1+0 would be 139? It just goes through and changes n each time it encounters a number, stops at each . and then when it gets to the end, TOTAL does nothing? So watching n as it went through, it would be "0" for the first 7 lines, then it would proceed through each integer, 1-18, and remain at 18 for the last line?
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