[SOLVED] Bash Scripting - Question regarding if statement.

z1lt0id · 2013-12-09 04:46:55

I have a bash script where it asks you how many video files you want to concat together. It asks you how many video files there are and then does the following

if [ "$segments_variable" = "2" ]; then
        ffmpeg -i "concat:01.h264|02.h264" -c copy video.h264
fi
if [ "$segments_variable" = "3" ]; then
        ffmpeg -i "concat:01.h264|02.h264|03.h264" -c copy video.h264
fi
if [ "$segments_variable" = "4" ]; then
        ffmpeg -i "concat:01.h264|02.h264|03.h264|04.h264" -c copy video.h264
fi

How would I make it so you could put in say 40 and it would be able to do it without make 40 if statements?

Last edited by z1lt0id (2013-12-09 22:28:58)

ewaller · 2013-12-09 04:53:13

A for loop comes to immediately to mind. Second Duck-Duck-Go hit on "Bash for loop" : http://www.thegeekstuff.com/2011/07/bas … -examples/

z1lt0id · 2013-12-09 04:58:14

I understand how you would use a loop function, but I guess where I am more stumped is with how to add to the ffmpeg line where I need to add

concat:01.h264|02.h264|03.h264| etc etc

That is what has me stumped.

Scimmia · 2013-12-09 05:03:11

This is perfect for a case statement.

nevermind, didn't read. Are the files always named with numbers like that or are you just using that to demonstrate?

Last edited by Scimmia (2013-12-09 05:06:29)

z1lt0id · 2013-12-09 05:05:46

But wouldn't a case statment be like

2)
 ffmpeg -i "concat:01.h264|02.h264" -c copy video.h264;
3)
 ffmpeg -i "concat:01.h264|02.h264|03.h264" -c copy video.h264;

ewaller · 2013-12-09 05:05:47

I see what you are asking. Build the 01.h264|02.h264|03.h264|04.h264..... string inside the for loop and call it something, say $CATSTRING. After you fall outside the loop, then do something like:
ffmpeg -i $CATSTRING -c copy video.h264

Scimmia · 2013-12-09 05:34:16

If those are the actual names, you don't even need a loop, just bash brace expansion.

filelist=$(echo {01..$1}.h264)
ffmpeg -i "concat:${filelist// /|}" -c copy video.h264

z1lt0id · 2013-12-09 08:24:07

Interesting enough. When I use a variable in the first line it will come out for example as {01..06}.h264 instead 01.h264 02.h264 03.h264, etc.

lolilolicon · 2013-12-09 10:08:14

Scimmia wrote:

filelist=$(echo {01..$1}.h264)

This doesn't work because brace expansion is done before parameter expansion. One way around this is using eval, of course.

@z1lt0id

I don't know your convention for leading zeros (always pad to length 2? how about 100.h264 then?); just an example:

#!/bin/bash

segments_variable=10

segments_list=
for ((i=1; i<=segments_variable; i++)); do
  segments_list+=$(printf '%0*d.h264|' ${#segments_variable} "$i")
done
segments_list=${segments_list%\|}

ffmpeg -i "concat:$segments_list" -c copy video.h264

z1lt0id · 2013-12-09 10:28:27

I realised padding makes no sense in that regard. But it would never get to 100 segments. But thanks for the below example I'll try it out and adapt it.

satanselbow · 2013-12-09 10:51:07

Would it not be more sane (portable) to feed your script the video files from the command line?

You could then make use of bash's "$@" as an array to feed your looped concat..

fileArray=("$@")

for arg in "${fileArray[@]}"; do
   echo "$arg" // do your concat here as per lolilolicon/Scimmia
done

There are numerous bash tutorials knocking about to do this sort of iteration... google is your friend...

lolilolicon · 2013-12-09 11:42:43

z1lt0id wrote:

I realised padding makes no sense in that regard.

In the absence of zero padding, an IFS trick would be more convenient:

#!/bin/bash

segments_variable=10

eval segments=\({1..$segments_variable}.h264\)

ifs=$IFS
IFS='|'
ffmpeg -i "concat:${segments[*]}" -c copy video.h264
IFS=$ifs

Scimmia · 2013-12-09 16:59:16

lolilolicon wrote:

Scimmia wrote:
filelist=$(echo {01..$1}.h264)
This doesn't work because brace expansion is done before parameter expansion. One way around this is using eval, of course.

Ah, I was testing in zsh, where it works perfectly. Forgot to try it in bash.

z1lt0id · 2013-12-09 22:28:39

lolilolicon wrote:

Scimmia wrote:
filelist=$(echo {01..$1}.h264)
This doesn't work because brace expansion is done before parameter expansion. One way around this is using eval, of course.
@z1lt0id
I don't know your convention for leading zeros (always pad to length 2? how about 100.h264 then?); just an example:
#!/bin/bash

segments_variable=10

segments_list=
for ((i=1; i<=segments_variable; i++)); do
  segments_list+=$(printf '%0*d.h264|' ${#segments_variable} "$i")
done
segments_list=${segments_list%\|}

ffmpeg -i "concat:$segments_list" -c copy video.h264

This actually works perfectly Thank you to everyone that helped me out.

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#1 2013-12-09 04:46:55

[SOLVED] Bash Scripting - Question regarding if statement.

#2 2013-12-09 04:53:13

Re: [SOLVED] Bash Scripting - Question regarding if statement.

#3 2013-12-09 04:58:14

Re: [SOLVED] Bash Scripting - Question regarding if statement.

#4 2013-12-09 05:03:11

Re: [SOLVED] Bash Scripting - Question regarding if statement.

#5 2013-12-09 05:05:46

Re: [SOLVED] Bash Scripting - Question regarding if statement.

#6 2013-12-09 05:05:47

Re: [SOLVED] Bash Scripting - Question regarding if statement.

#7 2013-12-09 05:34:16

Re: [SOLVED] Bash Scripting - Question regarding if statement.

#8 2013-12-09 08:24:07

Re: [SOLVED] Bash Scripting - Question regarding if statement.

#9 2013-12-09 10:08:14

Re: [SOLVED] Bash Scripting - Question regarding if statement.

#10 2013-12-09 10:28:27

Re: [SOLVED] Bash Scripting - Question regarding if statement.

#11 2013-12-09 10:51:07

Re: [SOLVED] Bash Scripting - Question regarding if statement.

#12 2013-12-09 11:42:43

Re: [SOLVED] Bash Scripting - Question regarding if statement.

#13 2013-12-09 16:59:16

Re: [SOLVED] Bash Scripting - Question regarding if statement.

#14 2013-12-09 22:28:39

Re: [SOLVED] Bash Scripting - Question regarding if statement.

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