База знаний » GNU/Linux

Wiki »

Base64cp » История » Редакция 3

Редакция 2 (Андрей Волков, 2013-06-03 19:43) → Редакция 3/4 (Андрей Волков, 2013-06-03 19:46)

h1. Передача бинарных файлов текстом 

 h2. Декодировщик средствами bash 

 *base64decode.sh* 

 <pre> 
 #!/bin/bash 

  # Base64 decoding routine written entirely in bash, with no external dependencies.  
  # 
  # Usage: 
  # base64decode < input > output 
  # 
  # This code is absurly inefficient; it runs aproximately 12,000 times slower than 
  # the perl-based decoder. The difference is that this code doesn't require you to 
  # install any external programs, which may be important in some cases. 
  # 
  # To decode using perl instead, use the following: 
  #  
  # base64decode() { 
  # perl -e 'use MIME::Base64 qw(decode_base64);$/=undef;print decode_base64(<>);' 
  # } 
  # 

  base64decode() { 
      L=0 
      A=0 
      P=0 
      while read -n1 C ; do 
          printf -v N %i \'"$C" 
          if (( $N == 61 )) ; then 
              P=$(( $P + 1 )) # = (padding) 
              V=0 
          elif (( $N == 43 )) ; then 
              V=62 # + 
          elif (( $N == 47 )) ; then 
              V=63 # / 
          elif (( $N < 48 )) ; then 
              continue 
          elif (( $N < 58 )) ; then 
              V=$(( $N + 4 )) # -48 + 52 (0-9) 
          elif (( $N < 65 )) ; then 
              continue 
          elif (( $N < 91 )) ; then 
              V=$(( $N - 65 )) # -65 + 0 (A-Z) 
          elif (( $N < 97 )) ; then 
              continue 
          elif (( $N < 123 )) ; then 
              V=$(( $N - 71 )) # -97 + 26 (a-z) 
          else 
              continue 
          fi 
             
          A=$(( ($A << 6) | $V )) 
          L=$(( $L + 1 ))  

          if [ $L == 4 ] ; then 
              printf -v X "%x" $(( ($A >> 16) & 0xFF )) 
              printf "\x$X" 
              if (( $P < 2 )) ; then 
                  printf -v X "%x" $(( ($A >> 8) & 0xFF )) 
                  printf "\x$X" 
              fi 
              if (( $P == 0 )) ; then 
                  printf -v X "%x" $(( $A & 0xFF )) 
                  printf "\x$X" 
              fi  
              A=0 
              L=0 
              P=0 
          fi 
      done 
  } 

 base64decode 
 </pre> 

 Прием файла 

 read -d : data 

 Вставляем текст и нажимаем ":" 

 echo "${data}" > file.b64 

 . base64decode.sh < file.b64 > file.bin