How to escape this in the bash script?

Question

I'm trying to complete a batch of 3 videos to leave it there till morning processing but it seems there are special characters in it... I try it "raw" in the terminal and it works but in bash script it stops working

Example:

args1="-r 29.97 -t 00:13:30 -vsync 0 -vpre libx264-medium -i"
args12="-r 29.97 -ss 00:40:30 -vsync 0 -vpre libx264-medium -i"
args2="[in] scale=580:380 [T1],[T1] pad=720:530:0:50 (other arguments with lots of [ and ]"

In the output it says

Unable to find a suitable output format for 'scale=580:380' not sure why... like I said, the command runs fine in the command-line, just not in the script

/usr/local/bin/ffmpeg "$args1" "${file}"  -vf "$args2" "$args3" "${args[0]}_${startingfrom}_0001_02.mp4"

Answer 1

Don't put more than one argument in a variable, it will work for very simple cases, but otherwise give you nothing but grief. Use arrays instead. E.g.

infile=video.avi
outfile=${infile%.*}.mp4  # video.mp4
args=(
    -r 29.97 
    -t 00:13:30 
    -vsync 0 
    -vpre libx264-medium 
    -vf "[in] scale=580:380 [T1],[T1] pad=720:530:0:50"
)
#...
ffmpeg -i "$infile" "${args[@]}" "$outfile"

(The quotes are important)

In this case though, you might want a function instead. It's hard to say, since your question is a bit vague.

See BashFAQ 50

Answer 2

It looks like $args1 and $args12 contain several options but $args2 looks like it should be a single value for the -vf option. So you should omit the quotes from $args1 and $args12 so they are subject to word splitting, but continue to quote $args2.

However, the error message you report "Unable to find a suitable output format for 'scale=580:380'" looks like it is coming from ffmpeg and not the shell.

Answer 3

In this case, where you want $argsN to be passed to ffmpeg as multiple arguments you actually don't want to quote it. To be clear, you do want to quote the line where you are setting it, so:

args1="-r 29.97 -t 00:13:30 -vsync 0 -vpre libx264-medium -i" 

Is correct. But the ffmpeg line should look something like this:

/usr/local/bin/ffmpeg $args1 "${file}"  -vf $args2 $args3 "${args[0]}_${startingfrom}_0001_02.mp4"

The problem here is that ffmpeg is expecting an array of arguments like this:

0: /usr/local/bin/ffmpeg
1: -r
2: 29.97
3: -t
...

When you quote the variable containing the arguments they are all sent in as a single argument like this:

0: /usr/local/bin/ffmpeg
1: -r 29.97 -t 00:13:30 -vsync 0 -vpre libx264-medium -i
...

Since ffmpeg has no single option, -r 29.97 -t 00:13:30 -vsync 0 -vpre libx264-medium -i it rightfully complains.

If you want to play around with being able to see how exactly your arguments are being passed you can use this simple shell script which prints each argument passed to it on a separate line:

#!/bin/bash
echo "0: $0"
i=1
for argument in "$@"; do
    echo "${i}: $argument"
    ((i++))
done

Answer 4

Maybe you should try to define your args thus:

args2='[in] scale= .....'

(note the single quote as opposed to the double quote). Say how you get on.