cut


Using a CSV input file, find all documents that contain any of the items in a cell of a column

The following code will use as input one column from a CSV file, and for each element in the column, it will perform a full-text search in a folder to find all files that contain that element.

#!/bin/bash

#Execution parameters
# 1 - the folder to look in for the element
# 2 - the input file that contains the search terms
# 3 - the column of interest
# 4 - the delimiter to use to find the column
# e.g. ./searchEachElement.sh ./2\ Print/ book.csv 5 ','

folder="$1";
input="$2";
column="$3";
delimiter="$4"

while read -r line; do
  needle=`echo $line | cut -d "$delimiter" -f "$column"`; 
  echo ">>> $needle"
  find "$folder" -type f -exec grep "$needle" -s -l '{}' \;
done < "$input";

More information on the full-text search can be found here.


Cut a video based on start and end time using FFmpeg

You probably don’t have a keyframe at the specified second mark if you can’t cut a video at a particular moment.
Non-keyframes need all of the data beginning with the previous keyframe because they encode variations from other frames.

Using an edit list, it is possible to cut at a non-keyframe with the mp4 container without re-encoding.
In other words, if the closest keyframe before 3s is at 0s, the video will be copied starting at 0s, and FFmpeg will use an edit list to tell the player to begin playing 3 seconds in.

If you’re using the latest version of FFmpeg from git master, it’ll use an edit list when you run it with the command you give.
If this does not work for you, it is you are likely using an older version of FFmpeg or that your player does not support edit lists.
Some players can disregard the edit list and play the entire file from beginning to end, regardless of the edit list.

If you want to cut specifically at a non-keyframe and have it play at the desired point on a player that doesn’t support edit lists, or if you want to make sure the cut section isn’t in the output file (for example, if it includes sensitive information), you can do so by re-encoding so that a keyframe is present at the desired start time.
If you don’t mention copy, re-encoding is the norm.
Consider the following scenario:

ffmpeg -i input.mp4 -ss 00:00:07 -t 00:00:18 -async 1 output.mp4
  • The -t option defines a length rather than an end time.
  • The command above will encode 18 seconds of video beginning at 7 seconds.
  • Use -t 8 to start at 7 seconds and end at 15 seconds.
  • If you’re using a recent version of FFmpeg, you can also use -to instead of -t in the above command to make it end at the required time.

Bash: Remove the last character from each line 1

The following script, uses rev and cut to remove the last character from each line in a pipe.
rev utility reverses lines character-wise.
cut removes sections  from each of line.
It is a very simple script where we reverse the line once, remove the first character (which was the last one in the original form of the line) and finally we reverse the line back with the last character missing.

echo -e "hi\nHI" | rev | cut -c 2- | rev;

# Will produce:
h
H

 


How to find the program interpreter that a Linux application requests 1

Recently we tried to execute an application and we got the following error:
-bash: ./main: No such file or directory
This error occurred because our application was trying to use an interpreter that was not available on that machine.
We used the readelf utility that displays information about ELF files (including the interpreter information) to resolve our issue.
Specifically we used readelf -l ./main which displays the information contained in the file’s segment headers, if it has any.
(You can replace the parameter -l with --program-headers or --segments, they are the same).

From the data that was produced we only needed the following line:

[Requesting program interpreter: /lib/ld-linux-armhf.so.3]
so we used grep to filter out all other lines and then cut and tr to get the data after the : character (second column) and then remove all spaces and the ] character from the result.
The full and final command we used was:
readelf -l ./main | grep 'Requesting' | cut -d':' -f2 | tr -d ' ]';