limit-rate: shell skript for the speed surveillance of a (file/pipe) transfer

After having uploaded lines/getline recently, now I upload another nice thing: limit-rate!

It's task is to control (i. e. to slow down) the speed of a transfer (can be a file copy operation or a pipe transfer).

The main technique used for that is:

• Copy a block of data with dd in continuous time periods. (dd is a "driver" here; maybe it would be better to write a better fitting alternative or - im waiting for that! - write an alternative with confusion free and understandable command line interface.)

• The copy operations are surveilled. When they lag because of the system, a "dry" status is activated. When the rate isn't right, either the block size or the period are changed.

Unfortunately the script is not finished at all. As user you may need to adapt it to your requirements and the actual system. (E. g. allow even shorter time periods than set up by default.)

How it works is visualized below by a nices sample run. Have fun playing with the script!

Remark: only use the program in a private scope.

Verwendung (Linux, BSD, Windows (cygwin), OS X (?)):

1. Herunterladen: Version 1.03
2. In ein neues/leeres Verzeichnis (!) entpacken (Unpack into an empty dir!)
3. Uund ... ausführen!

   # (echo 1000 >RATE.tmp; sleep 10; echo 800000 >RATE.tmp) & sleep 0.2; ./limit-rate.sh src=/.../Filme/.../big-movie-file.avi tgt=/dev/null ratefile=RATE.tmp
   [4] 25579
   ./limit-rate.sh: src = '/.../Filme/.../big-movie-file.avi'
   ./limit-rate.sh: tgt = '/dev/null'
   ./limit-rate.sh: rate = 1024 B/s
   copy-file: rate:    15360/    [15360]/     1024      -> time 100, dd_bs   1024
   copy-file: rate:     8192/     [8192]/     1000      -> time 200, dd_bs   1024
   copy-file: rate:     5120/     [5120]/     1000      -> time 400, dd_bs   1024
   copy-file: rate:     2048/     [2048]/     1000      -> time 400, dd_bs    512
   copy-file: rate:     1536/     [1536]/     1000      -> time 400, dd_bs    256
   copy-file: rate:      512/      [512]/     1000      -> time 200, dd_bs    256
   copy-file: rate:     1024/     [1024]/     1000      -> time 220, dd_bs    231
   copy-file: rate:      924/      [924]/     1000      -> time 198, dd_bs    254
   copy-file: rate:     1270/     [1270]/     1000      -> time 217, dd_bs    229
   copy-file: rate:      916/      [916]/     1000      -> time 196, dd_bs    251
   copy-file: rate:     1255/     [1255]/   800000      -> time  98, dd_bs    251
   copy-file: rate:     1757/     [1757]/   800000      -> time  49, dd_bs    251
   copy-file: rate:     3514/     [3514]/   800000      -> time  24, dd_bs    251
   copy-file: rate:     5271/     [5271]/   800000      -> time  12, dd_bs    251
   copy-file: rate:     7028/     [7028]/   800000      -> time  12, dd_bs    502
   copy-file: rate:    14558/    [14558]/   800000      -> time  12, dd_bs   1004
   copy-file: rate:    28112/    [28112]/   800000      -> time  12, dd_bs   2008
   copy-file: rate:    58232/    [58232]/   800000      -> time  12, dd_bs   4016
   copy-file: rate:   116464/   [116464]/   800000      -> time  12, dd_bs   8032
   copy-file: rate:   224896/   [224896]/   800000      -> time  12, dd_bs  16064
   copy-file: rate:   449792/   [449792]/   800000      -> time  12, dd_bs  32128
   copy-file: rate:   899584/   [899584]/   800000      -> time  13, dd_bs  28916
   copy-file: rate:   809648/   [809648]/   800000      -> time  14, dd_bs  26025
   copy-file: rate:   702675/   [702675]/   800000      -> time  13, dd_bs  28627
   copy-file: rate:   744302/   [744302]/   800000      -> time  12, dd_bs  31489
   copy-file: rate:   881692/   [881692]/   800000      -> time  13, dd_bs  28341
   copy-file: rate:   793548/   [793548]/   800000      -> time  12, dd_bs  31175
   copy-file: rate:   872900/   [872900]/   800000      -> time  13, dd_bs  28058
   copy-file: rate:   757566/   [757566]/   800000      -> time  12, dd_bs  30863
   copy-file: rate:   833301/   [833301]/   800000      -> time  13, dd_bs  27777
   copy-file: rate:   722202/   [722202]/   800000      -> time  12, dd_bs  30554
   copy-file: rate:   886066/   [886066]/   800000      -> time  13, dd_bs  27499
   ^C[4]+  Fertig                  ( echo 1000 > RATE.tmp; sleep 10; echo 800000 > RATE.tmp )
   
    130  ((echo 1000 >RATE.tmp; sleep 10; echo 800000 >RATE.tmp) & sleep 0.2; ....)
   #