База знаний » GNU/Linux

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>