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Full Discussion: bash: read file line by line (lines have '\0') - not full line has read???
Top Forums Shell Programming and Scripting bash: read file line by line (lines have '\0') - not full line has read??? Post 302412910 by rowanthorpe on Wednesday 14th of April 2010 01:26:57 AM
Old 04-14-2010
I realise this thread is over a month old, but I'll add my input even if it's no longer useful to the original poster, but just for others browsing. I realise the following code is far from elegant (ugly would be a good word), but it "works" (namely, it allows you to read full lines including nulls into a string for processing, one line at a time, without losing the nulls, using only Bash builtins).

Bash treats strings the same as C does (null-terminated), so it is obviously impossible to read in strings containing true nulls. The following code only breaks from the loop when the "read" command returns null (\0) twice in a row without other intervening text. It optionally adds an escaped null back into the string with each non-terminal read.

Generally it is far less painful to use something like Perl for this, but if you really are stuck in Bash and need a solution without external tools, maybe this will help.

Code:
printf \
  "hello\0word\0done\0\n"\
  "this\0next\0line\0\n"\
  "last\0ln\n"\
  > grb
buffer=""
xtra=""
while IFS= read -r -d '' ln; do
  buffer+="$xtra"
  ## If you wish to re-include the nulls as \0, which will work
  ## when you output with "printf", do this
  if [[ -n "$buffer" ]]; then
    buffer+="\0"
    ## otherwise
    #buffer+=" "
  fi
  buffer+="${ln%%$'\n'*}"
  xtra="${ln#*$'\n'}"
  if [[ "${ln/$'\n'}" != "$ln" ]]; then
    ## USE "$buffer" HERE HOWEVER YOU WISH
    printf "${buffer}\n" ## ..for example
    ## ...TILL HERE
    buffer=""
  else
    xtra=""
  fi
done <grb

Quote:
(And, it seems to me, there is some glitch in bash-2.05 in processing pipe by while (something about that I've experiensed about half year ago.) Seems something with asigning variables...
So, another point why I do not like that solution by 'tr..'
When bash reads from a pipe it spawns a subshell, so any variables you assign within the subshell will disappear after the command/loop which reads from the pipe finishes. It's not a "glitch", it's a feature. Using shell redirection avoids this. For example:

Code:
blob=""
while read temp; do
  blob+="$temp"
done < filename
echo "$blob"

will work, but:

Code:
blob=""
cat filename | while read temp; do
  blob+="$temp"
done
echo "$blob"

will not.
 

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LEARN ABOUT MINIX

pwdauth

PWDAUTH()																 PWDAUTH()

NAME

       pwdauth - password authentication program

SYNOPSIS

       /usr/lib/pwdauth

DESCRIPTION

       Pwdauth is a program that is used by the crypt(3) function to do the hard work.	It is a setuid root utility so that it is able to read the
       shadow password file.

       Pwdauth expects on standard input two null terminated strings, the password typed by the user, and the salt.  That is, the two arguments of
       the  crypt  function.   The input read in a single read call must be 1024 characters or less including the nulls.  Pwdauth takes one of two
       actions depending on the salt.

       If the salt has the form "##user" then the user is used to index the shadow password file to obtain  the  encrypted  password.	The  input
       password  is encrypted with the one-way encryption function contained within pwdauth and compared to the encrypted password from the shadow
       password file.  If equal then pwdauth returns the string "##user" with exit code 0, otherwise exit code 2 to signal  failure.   The  string
       "##user" is also returned if both the shadow password and the input password are null strings to allow a password-less login.

       If  the salt is not of the form "##user" then the password is encrypted and the result of the encryption is returned.  If salt and password
       are null strings then a null string is returned.

       The return value is written to standard output as a null terminated string of 1024 characters or less including the null.

       The exit code is 1 on any error.

SEE ALSO

       crypt(3), passwd(5).

NOTES

       A password must be checked like in this example:

	      pw_ok = (strcmp(crypt(key, pw->pw_passwd), pw->pw_passwd) == 0);

       The second argument of crypt must be the entire encrypted password and not just the two character salt.

AUTHOR

       Kees J. Bot (kjb@cs.vu.nl)

																	 PWDAUTH()
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