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Full Discussion: URL decoding with awk
Top Forums UNIX for Dummies Questions & Answers URL decoding with awk Post 302603389 by uiop44 on Wednesday 29th of February 2012 11:50:23 PM
Old 03-01-2012
URL decoding with awk
The challenge:

Decode URL's, i.e. convert %HEX to the corresponding special characters, using only UNIX base utilities, and without having to type out each special character.

I have an anonymous C code snippet where the author assigns each hex digit a number from 0 to 16 and then does some bit shifting. It works nicely.

Is there an easy way to do this with awk?

Wanna see an ugly hack? Well, here it is anyway. This attempt outputs a shell function called "ud" that purports to decode URL's piped through it. Not tested thoroughly.

Maybe this could be done with dc or bc (for hex->octal, then use awk for gsub) instead of xxd.

Code:
_ud(){
{
jot -w"printf '\%03d'|xxd -u" 178 000 177|sh ;
jot -w"printf '\%03d'|xxd -u" 178 000 177|sh\
 |dd conv=lcase 2>&- ;
} \
 |sed -e '
s/.*0: //;
/[A-Za-z0-9]$/d;
/^[01]/d;' \
 -e ':a' \
 -e 's/  / /;t a' \
 -e '
s, ,l,;
s,.*,sl%&lg,;
/2[Ff]/!s,ll,l+l,;
/5[Cc]/s,.,\"&\",7;
/22/s,\",\\",;
/26/s,&,\\&,;
/27/d;
' 
printf 'sl%%27l\047\"\047\"\047lg\n';
printf 's/&/\&/g\n'
}

ud(){
_ud \
 |sed '
1s,.*,ud(){\
sed '"'"'\
&,;
$s,.*,&\
'"'"';\
},
'

}

Yikes!
Last edited by uiop44; 03-01-2012 at 12:57 AM..
 

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LEARN ABOUT X11R4

printf

PRINTF(1)                                                          User Commands                                                         PRINTF(1)

NAME

       printf - format and print data

SYNOPSIS

       printf FORMAT [ARGUMENT]...
       printf OPTION

DESCRIPTION

       Print ARGUMENT(s) according to FORMAT, or execute according to OPTION:

       --help display this help and exit

       --version
              output version information and exit

       FORMAT controls the output as in C printf.  Interpreted sequences are:

       "     double quote

       \     backslash

       a     alert (BEL)

            backspace

       c     produce no further output

       e     escape

       f     form feed

       
     new line

       
     carriage return

       	     horizontal tab

       v     vertical tab

       NNN   byte with octal value NNN (1 to 3 digits)

       xHH   byte with hexadecimal value HH (1 to 2 digits)

       uHHHH Unicode (ISO/IEC 10646) character with hex value HHHH (4 digits)

       UHHHHHHHH
              Unicode character with hex value HHHHHHHH (8 digits)

       %%     a single %

       %b     ARGUMENT as a string with '' escapes interpreted, except that octal escapes are of the form  or NNN

       %q     ARGUMENT  is  printed  in  a format that can be reused as shell input, escaping non-printable characters with the proposed POSIX $''
              syntax.

       and all C format specifications ending with one of diouxXfeEgGcs, with ARGUMENTs converted to proper type first.  Variable widths are  han-
       dled.

       NOTE:  your  shell  may  have its own version of printf, which usually supersedes the version described here.  Please refer to your shell's
       documentation for details about the options it supports.

AUTHOR

       Written by David MacKenzie.

REPORTING BUGS

       GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
       Report printf translation bugs to <http://translationproject.org/team/>

COPYRIGHT

       Copyright (C) 2017 Free Software Foundation, Inc.  License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
       This is free software: you are free to change and redistribute it.  There is NO WARRANTY, to the extent permitted by law.

SEE ALSO

       printf(3)

       Full documentation at: <http://www.gnu.org/software/coreutils/printf>
       or available locally via: info '(coreutils) printf invocation'

GNU coreutils 8.28                                                 January 2018                                                          PRINTF(1)
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