appending a string constant selectively within a while loop in bash

Question

I have a script called automateutube that I edit in VIM and execute in the terminal with sh ./automateutube.sh This script pulls youtube links from a file called songs.txt and downloads the video from youtube then extracts the audio.

The songs.txt file looks like this

https://www.youtube.com/watch?v=IxQOlZ3pqtI
https://www.youtube.com/watch?v=IxQOlZ3pqtI
https://www.youtube.com/watch?v=IxQOlZ3pqtI
https://www.youtube.com/watch?v=IxQOlZ3pqtI

It is just a bunch of links, one per line.

The script looks like this

#!/bin/bash

while read p; do    

x=/tmp/.youtube-dl-$(date +%y.%m.%d_%H.%M.%S)-$RANDOM.flv

youtube-dl --audio-quality 160k --output=$x --format=18 "$p"

ffmpeg -i $x -acodec libmp3lame -ac 2 -ab 128k -vn -y "$p"

rm $x

done <songs.txt

Now the first part executes. It downloads the video and starts to unpack it.

It is the second part that fails. ffmpeg -i $x -acodec libmp3lame -ac 2 -ab 128k -vn -y "$p"

This is because "$p" is supposed to be in format "filename.mp3" However as it is p takes the value of a youtube link, without ".mp3" appended.

This works for the first line

youtube-dl --audio-quality 160k --output=$x --format=18 "$p"

because "$p" is supposed to be in the form of a link there.

Now I have tried adding three lines in

a="$.mp3"
b="$p"
c=$b$a

and making ffmpeg -i $x -acodec libmp3lame -ac 2 -ab 128k -vn -y "$p"

into ffmpeg -i $x -acodec libmp3lame -ac 2 -ab 128k -vn -y "$c"

but I am still getting an error. Any ideas?

parse error, at least 3 arguments were expected, only 1 given in string 'om/watch?v=sOAHOxbMOJY'

so the filenames supposed to be `https://www.youtube.com/watch?v=IxQOlZ3pqtI.mp3` ? — 123, Jan 28 '17 at 20:44
@123 yes that is supposed to be the file name. And I edited it. I meant "$.mp3" — Maxwell Chandler, Jan 28 '17 at 20:49
Why is there a dollar though? Also you can't have forward slashes in filenames... Might also be useful to post what error message you are getting. — 123, Jan 28 '17 at 20:49
@123 okay good point but either way that shouldn't matter because the .mp3 is still intact and the file extension — Maxwell Chandler, Jan 28 '17 at 20:53
@Gabriele yes I have tried that and I still get a parse error — Maxwell Chandler, Jan 28 '17 at 20:55
Whole lotta quoting bugs here. http://shellcheck.net/ is your friend. — Charles Duffy, Jan 28 '17 at 20:55
@123 well I have tried ".mp3" alone just now and its the same parse error. — Maxwell Chandler, Jan 28 '17 at 20:56
That said, `$p.mp3` will append `.mp3`. I'm not sure what the extra gymnastics you're doing are about. — Charles Duffy, Jan 28 '17 at 20:57
...could you build a reproducer that lets folks see your bug *without* needing `youtube-dl`, `ffmpeg`, etc? And **show your actual error**; don't just say you're "getting an error", but provide it in detail. Re: building a reproducer, see http://stackoverflow.com/help/mcve — Charles Duffy, Jan 28 '17 at 20:58
I don't understand why you are appending `FLV` onto the file, why not just use `mp3`... — l'L'l, Jan 28 '17 at 20:59
(aside: `bash -x yourscript` is your friend -- observing the actual commands that are run will help you figure out the first place where something isn't what you expect). — Charles Duffy, Jan 28 '17 at 20:59
okay thanks for all the feedback I will work on it and try to make a reproducer — Maxwell Chandler, Jan 28 '17 at 21:05
Also, you have used sh to run, what you have defined as, a bash script - by #!/bin/bash. Bash and sh are similar, but not the same. Check this: http://stackoverflow.com/questions/5725296/difference-between-sh-and-bash — Mr Goobri, Jan 28 '17 at 21:47

score 0 · Answer 1 · answered Jan 29 '17 at 00:56

0

So after some experimentation using advice from the comments, I came to this, which works.

#!/bin/sh

while read -r p; do    

x=/tmp/.youtube-dl-$(date +%y.%m.%d_%H.%M.%S)-$RANDOM.flv

youtube-dl --audio-quality 160k --output="$x" --format=18 "$p"

SUBSTRING=$(echo "$p"| cut -c33-50)

ffmpeg -i "$x" -acodec libmp3lame -ac 2 -ab 128k -vn -y "$SUBSTRING.mp3" </dev/null

rm "$x"

done <songs.txt

What this fixes is keeping /'s out of the file name, and eliminating parser error.

answered Jan 29 '17 at 00:56

Maxwell Chandler

626
8
18

2

You can replace the line `SUBSTRING=$(echo "$p"| cut -c33-50)` with `SUBSTRING="${p:32:18}"` to avoid creating a subshell that executes a command. – Jeffrey Cash Jan 29 '17 at 09:01

appending a string constant selectively within a while loop in bash

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