Bash Index : F - The 'F' Bash commands : description, flags and examples

List available codecs :

ffmpeg -codecs
V : video codec
A : audio codec
S : subtitle codec

This command returns a failure exit code as ffmpeg expects an "output file" parameter (I found no better solution so far ). For this reason ("failure" exit code + output message sent to stderr rather than stdout), you have to redirect everything to stdout before processing it :

for a single file :

ffmpeg -i file 2>&1 | grep 'Stream'

for multiple files :

streamType='Audio'; for mediaFile in *; do echo "$mediaFile"; ffmpeg -i "$mediaFile" 2>&1 | grep -E "Stream.*$streamType"; done

• workDir="/run/user/$UID"; df -h "$workDir"; echo; testFile="$workDir/test_1GiB"; fallocate -l 1g "$testFile"; ls -lh "$testFile"; du -h "$testFile"; echo; df -h "$workDir"; [ -f "$testFile" ] && rm "$testFile"

  Filesystem      Size  Used Avail Use% Mounted on
  tmpfs           3,1G  164K  3,1G   1% /run/user/1000
  
  -rw------- 1 bob developers 1,0G déc.  19 12:37 /run/user/1000/test_1GiB
  1,0G    /run/user/1000/test_1GiB	actual file size
  
  Filesystem      Size  Used Avail Use% Mounted on
  tmpfs           3,1G  1,1G  2,1G  33% /run/user/1000

• Alternate that creates a sparse file (source, details) :
  workDir="/run/user/$UID"; df -h "$workDir"; echo; testFile="$workDir/test_1GiB"; truncate -s 1g "$testFile"; ls -lh "$testFile"; du -h "$testFile"; echo; df -h "$workDir"; [ -f "$testFile" ] && rm "$testFile"

  Filesystem      Size  Used Avail Use% Mounted on
  tmpfs           3,1G  164K  3,1G   1% /run/user/1000
  
  -rw------- 1 bob developers 1,0G déc.  19 12:45 /run/user/1000/test_1GiB
  0       /run/user/1000/test_1GiB	actual file size
  
  Filesystem      Size  Used Avail Use% Mounted on
  tmpfs           3,1G  164K  3,1G   1% /run/user/1000

1. open a new terminal to experiment : you'll kill it at the end
2. destinationDir='/tmp'; bigFileSize='3G'; bigFile=$(mktemp --tmpdir="$destinationDir" .XXXXXXXXXXXXXXXX); df -h "$destinationDir"; fallocate -l "$bigFileSize" "$bigFile"; exec 4< "$bigFile"; rm "$bigFile"; df -h "$destinationDir"

   Filesystem                  Size  Used Avail Use% Mounted on
   /dev/mapper/vgxubuntu-root  914G   52G  816G   6% /		before
   Filesystem                  Size  Used Avail Use% Mounted on
   /dev/mapper/vgxubuntu-root  914G   55G  813G   7% /		after : +3GB used

3. try to ls it :
   ll "$bigFile"

   ls: cannot access '/tmp/.fKpHFCCUVWyxfSi2': No such file or directory

   You can't ls it because it's marked as deleted, even though it's not actually deleted yet because there's a process still using it.
4. list it with other means :
   lsof +L1 | grep "$destinationDir"

   
   bash      11107 kevin    4r   REG  252,1 3221225472     0 48758805 /tmp/.fKpHFCCUVWyxfSi2 (deleted)		the process holding $bigFile
   grep      15062 kevin    4r   REG  252,1 3221225472     0 48758805 /tmp/.fKpHFCCUVWyxfSi2 (deleted)		the grep right above

5. now, let's delete —actually release— it :
   kill -1 11107

   (the terminal closes)

6. in a new terminal :
   df -h '/tmp' must be the same dir as in step 2

   Filesystem                  Size  Used Avail Use% Mounted on
   /dev/mapper/vgxubuntu-root  914G   52G  816G   6% /		back to the "before" usage

1. alias '::'='fc -s ".:"="./"'
2. So the next time I type
   .:script.sh
   I'll get

   bash: .:script.sh: command not found

3. Then, using my new alias :
   ::
   fc fixes the typo and runs the command

   (normal output of script.sh)

Use cURL

		total	used	free	shared	buffers	cached
Mem:		16085	15884	200	0	347	12940
-/+ buffers/cache:	2596	13489
Swap:		1951	0	1951

1. the 1^st row (Mem:) is about physical memory utilization, including the amount of memory allocated to buffers and caches.
2. the 2^nd row (-/+ buffers/cache:) shows the amount of physical memory currently devoted to system buffers and cache. This is particularly meaningful with regard to application programs, as all data accessed from files on the system that are performed through the use of read() and write() system calls pass through this cache. This cache can greatly speed up access to data by reducing or eliminating the need to read from or write to the HDD or other disk.

Interpreting numbers :

buffers and caches :