I have an input file with 9095 lines of text. I need to take this list of filenames and use them as input to an ffmpeg command. I really would like to avoid running it all at once (line by line until end of file).
Is there a way in a bash script to take the first 25 lines, execute the ffmpeg command on them, then continue to the next 25 lines and execute the same command, until the end of the input file?
Input file (example.txt) has list of 9095 filenames to be processed.
I have tried the following:
#!/bin/bash
while mapfile -n 25 convert < example.txt do
while read -r line || [[ -n "$line" ]]; do fn_out="w$line"; (/path/to/file/ffmpeg -report -nostdin -i /path/to/file/watermark.png -i /path/to/file/"$line" -filter_complex "scale2ref[a][b];[b][a]overlay=x=(main_w-overlay_w)/2:y=(main_h-overlay_h)/2" /path/to/file/"$fn_out" -c:v libx265); done < $convert >> script.txt
done
This only gets me the first 25 files. How to account for all 9095 files in example.txt?
Also, is there any way to "pause" the script in between each set of 25 filenames? I am not familiar enough with mapfile and bash scripting to know how to handle this kind of iteration.
Basically, the output needs to be as follows:
- Read first 25 lines of example.txt
- Run the ffmpeg command on those 25 files (some files are over 2GB. Will take time to do the ffmpeg command.
- Pause for about a minute or two. Let server rest/catch up/recover resources.
- Get the next 25 names from example.txt
- Run the ffmpeg conversion loop again in step 2
- Continue until EOF of example.txt
Any direction on this would be greatly appreciated!
Running CentOS 7 with bash 5.0.17.
CodePudding user response：
You need to put the redirection around the entire loop, not just the mapfile line. Just like when you use while read to iterate through a file one line at a time.
while mapfile -n 25 convert; do
# code that uses $convert array
done < example.txt
Then each time through the loop it will get the next 25 lines of the file.
CodePudding user response：
With mapfile aka readarray, something like:
#!/usr/bin/env bash
num=25
while mapfile -tn "$num" files && (( ${#files[*]} == num )); do
for i in "${!files[@]}"; do
echo do_something_with "${files[$i]}"
done
sleep 60
done < file.txt
A simple test run.
num=25
while mapfile -tn "$num" files && (( ${#files[*]} == num )); do
for i in "${!files[@]}"; do
echo do_something_with "${files[$i]}"
done
echo ===
done < <(printf '%s\n' {1..9000})
Output:
do_something_with 1
do_something_with 2
do_something_with 3
do_something_with 4
do_something_with 5
do_something_with 6
do_something_with 7
do_something_with 8
do_something_with 9
do_something_with 10
do_something_with 11
do_something_with 12
do_something_with 13
do_something_with 14
do_something_with 15
do_something_with 16
do_something_with 17
do_something_with 18
do_something_with 19
do_something_with 20
do_something_with 21
do_something_with 22
do_something_with 23
do_something_with 24
do_something_with 25
===
do_something_with 26
do_something_with 27
do_something_with 28
do_something_with 29
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===
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===
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===
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- The
(( ${#files[*]} == num ))will execute the loop if it is true, if that is not desired just test if the arrayfileshas a value (regardless if it is less than 25 elements), change it to(( ${#files[*]} ))
CodePudding user response：
Assumptions/understandings:
- files are to be processed one-at-a-time and serially
- after a batch of 25 files have been processed sleep for 60 seconds
One bash approach using a simple counter (and no need for an array):
maxcnt=25
fcnt=0
while read -r fname
do
echo "run ffmpeg against $fname"
(( fcnt % maxcnt == 0)) && sleep 60
done < file.txt
Setup a small demo:
- 10 filenames in
file.txt - process 3 files and then sleep
- sleep for 2 seconds (also print message 'sleep 2')
Run the demo:
$ printf "file%s\n" {1..10} > file.txt
$ cat file.txt
file1
file2
file3
file4
file5
file6
file7
file8
file9
file10
$ maxcnt=3; fcnt=0
$ while read -r fname; do echo "run ffmpeg against $fname"; (( fcnt % maxcnt == 0)) && echo "sleep 2" && sleep 2; done < file.txt; echo "Done."
run ffmpeg against file1
run ffmpeg against file2
run ffmpeg against file3
sleep 2
run ffmpeg against file4
run ffmpeg against file5
run ffmpeg against file6
sleep 2
run ffmpeg against file7
run ffmpeg against file8
run ffmpeg against file9
sleep 2
run ffmpeg against file10
Done.