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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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LEARN ABOUT DEBIAN

chsh

CHSH(1) 							   User Commands							   CHSH(1)

NAME

       chsh - change login shell

SYNOPSIS

       chsh [options] [LOGIN]

DESCRIPTION

       The chsh command changes the user login shell. This determines the name of the user's initial login command. A normal user may only change
       the login shell for her own account; the superuser may change the login shell for any account.

OPTIONS

       The options which apply to the chsh command are:

       -h, --help
	   Display help message and exit.

       -R, --root CHROOT_DIR
	   Apply changes in the CHROOT_DIR directory and use the configuration files from the CHROOT_DIR directory.

       -s, --shell SHELL
	   The name of the user's new login shell. Setting this field to blank causes the system to select the default login shell.

       If the -s option is not selected, chsh operates in an interactive fashion, prompting the user with the current login shell. Enter the new
       value to change the shell, or leave the line blank to use the current one. The current shell is displayed between a pair of [ ] marks.

NOTE

       The only restriction placed on the login shell is that the command name must be listed in /etc/shells, unless the invoker is the superuser,
       and then any value may be added. An account with a restricted login shell may not change her login shell. For this reason, placing /bin/rsh
       in /etc/shells is discouraged since accidentally changing to a restricted shell would prevent the user from ever changing her login shell
       back to its original value.

FILES

       /etc/passwd
	   User account information.

       /etc/shells
	   List of valid login shells.

       /etc/login.defs
	   Shadow password suite configuration.

SEE ALSO

       chfn(1), login.defs(5), passwd(5).

shadow-utils 4.1.5.1						    05/25/2012								   CHSH(1)
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