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Full Discussion: Running ffmpeg in loop seems to change reading from file
Top Forums Shell Programming and Scripting Running ffmpeg in loop seems to change reading from file Post 302623733 by Thriceguy on Saturday 14th of April 2012 12:36:48 PM
Old 04-14-2012
Running ffmpeg in loop seems to change reading from file
Hi everyone,

I am fairly new to shell scripting. I want to read in numbers from a file (one number per line). This works perfectly fine

Code:
  
while read CurrentLine
do
echo $CurrentLine
done < myfile

and yields the correct output:

Code:
 
272
745
123

If I however run a ffmpeg command in the loop

Code:
  
while read CurrentLine
do
echo $CurrentLine
ffmpeg -sameq -vframes 1 -ss 2 -i PMI_thin_02.avi -f image2  a_b.png
done < myfile

the output changes (I ommit the ffmpeg output and just give the echo command output):

Code:
 
272
5
3

If I add two spaces in the txt-file I read in, such as

Code:
 
272
  745
  123

the echo command returns the right numbers again - for some reason, the ffmpeg commands seems to result in the skipping of the first two characters in the new line.
If I put an additional for-loop around the while loop to loop over several files such as in

Code:
 
for FileName in *.txt; do
	while read CurrentLine
	do
	echo $CurrentLine
ffmpeg -sameq -vframes 1 -ss 2 -i PMI_thin_02.avi -f image2  a_b.png
	done < "${FileName}"

The first line of every file is read in correctly, but for all subsequent lines, the first two characters are skipped. Does anybody have any idea what is going on? I am very grateful for any hint.

Best,
Thriceguy
 

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echo

ECHO(1) 								FSF								   ECHO(1)

NAME

       echo - display a line of text

SYNOPSIS

       echo [OPTION]... [STRING]...

DESCRIPTION

       NOTE:  your shell may have its own version of echo which will supercede the version described here. Please refer to your shell's documenta-
       tion for details about the options it supports.

       Echo the STRING(s) to standard output.

       -n     do not output the trailing newline

       -e     enable interpretation of the backslash-escaped characters listed below

       -E     disable interpretation of those sequences in STRINGs

       --help display this help and exit

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	      output version information and exit

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       NNN   the character whose ASCII code is NNN (octal)

       \     backslash

       a     alert (BEL)

            backspace

       c     suppress trailing newline

       f     form feed

       
     new line

       
     carriage return

       	     horizontal tab

       v     vertical tab

AUTHOR

       Written by FIXME unknown.

REPORTING BUGS

       Report bugs to <bug-coreutils@gnu.org>.

COPYRIGHT

       Copyright (C) 2002 Free Software Foundation, Inc.
       This is free software; see the source for copying conditions.  There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICU-
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SEE ALSO

       The  full documentation for echo is maintained as a Texinfo manual.  If the info and echo programs are properly installed at your site, the
       command

	      info echo

       should give you access to the complete manual.

GNU coreutils 4.5.3						   February 2003							   ECHO(1)
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