I need a file with a specific size and so that it has a valid base64. After this command, the file does not open (and therefore does not fit):

dd if=/dev/zero of=file.trash bs=1M count=20

How to do right?

  • It opens perfectly, check the rights to it. And in order to have a valid b64 there, obviously, this b64 will be generated and written there. - PinkTux
  • one
    Since base64 makes 3 bytes of 4, then any size can not be. valid. Specify, do you want to set the file size with base64 or before it? - avp
  • And what are you interested in? Open? Base64. Write your base64 decoding function that ignores the incorrectly decoded remainder and expands everything before it - Mike
  • truncate as already suggested below. - 0andriy

2 answers 2

Use the truncate command:

From man:

 truncate -s, --size=РАЗМЕР установить или подогнать размер файла под РАЗМЕР байт

Example:

 $ touch test.txt $ ls -l test.txt -rw-r--r-- 1 user user 0 окт 28 13:08 test.txt $ truncate -s 1048576 test.txt $ ls -lh test.txt -rw-r--r-- 1 user user 1,0M окт 28 13:08 test.txt

For clarity, the definition of base64 cut the file to 1K:

 $ ls -lh test.txt -rw-r--r-- 1 user user 1,0K окт 28 13:09 test.txt $ base64 test.txt AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA== 
     yes AAAA AAAA AAAA AAAA AAAA AAAA AAAA AAAA | dd of=file.trash bs=1K count=20K

    Here it is important that bs be no more than 4K, this is due to the output buffer size yes .