How to trim bytes from the beginning and end of a file

Jim's answer explains how to test for a symlink: by using test's -L test.

But testing for a "hard link" is, well, strictly speaking not what you want. Hard links work because of how Unix handles files: each file is represented by a single inode. Then a single inode has zero or more names or directory entries or, technically, hard links (what you're calling a "file").

Thankfully, the stat command, where available, can tell you how many names an inode has.

So you're looking for something like this (here assuming the GNU or busybox implementation of stat):

if [ "$(stat -c %h -- "$file")" -gt 1 ]; then
    echo "File has more than one name."
fi

The -c '%h' bit tells stat to just output the number of hardlinks to the inode, i.e., the number of names the file has. -gt 1 then checks if that is more than 1.

Note that symlinks, just like any other files, can also be linked to several directories so you can have several hardlinks to one symlink.

I finally found the time to try the answer suggested by @Mario G., but it seemed extremely cumbersome. I need to do this many dozens of times. I read the documentation of ffmpeg and found it much more powerful than avconv, including fading for audio and video, so the solution is

ffmpeg -i input.mts -map 0:0 -map 0:3 -ss 0:0:07 -to 0:59:57.5 -vf 'fade=t=in:st=7:d=2,fade=t=out:st=3595.5:d=2,crop=out_h=692' -af 'afade=t=in:st=7:d=2,afade=t=out:st=3595.5:d=2' out.mov

So the st= and d= parameters for the fade take times in seconds, no need for converting to frames.

I also discovered the -to option to take the end time directly instead of calculating the length.

This command does all steps

• channel selection with -map,
• trimming with -ss and -to,
• video fading with -vf option fade=t=in and fade=t=out,
• audio fading with -af option afade=t=in and afade=t=out and
• cropping with -vf option crop=

in a single step.