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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(1B)					     SunOS/BSD Compatibility Package Commands						  echo(1B)

NAME
echo - echo arguments to standard output SYNOPSIS
/usr/ucb/echo [-n] [argument] DESCRIPTION
echo writes its arguments, separated by BLANKs and terminated by a NEWLINE, to the standard output. echo is useful for producing diagnostics in command files and for sending known data into a pipe, and for displaying the contents of envi- ronment variables. For example, you can use echo to determine how many subdirectories below the root directory (/) is your current directory, as follows: o echo your current-working-directory's full pathname o pipe the output through tr to translate the path's embedded slash-characters into space-characters o pipe that output through wc -w for a count of the names in your path. example% /usr/bin/echo "echo $PWD | tr '/' ' ' | wc -w" See tr(1) and wc(1) for their functionality. The shells csh(1), ksh(1), and sh(1), each have an echo built-in command, which, by default, will have precedence, and will be invoked if the user calls echo without a full pathname. /usr/ucb/echo and csh's echo() have an -n option, but do not understand back-slashed escape characters. sh's echo(), ksh's echo(), and /usr/bin/echo, on the other hand, understand the black-slashed escape characters, and ksh's echo() also understands a as the audible bell character; however, these commands do not have an -n option. OPTIONS
-n Do not add the NEWLINE to the output. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWscpu | +-----------------------------+-----------------------------+ SEE ALSO
csh(1), echo(1), ksh(1), sh(1), tr(1), wc(1), attributes(5) NOTES
The -n option is a transition aid for BSD applications, and may not be supported in future releases. SunOS 5.10 3 Aug 1994 echo(1B)
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