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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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wc

WC(1)								   User Commands							     WC(1)

NAME

       wc - print newline, word, and byte counts for each file

SYNOPSIS

       wc [OPTION]... [FILE]...
       wc [OPTION]... --files0-from=F

DESCRIPTION

       Print  newline, word, and byte counts for each FILE, and a total line if more than one FILE is specified.  With no FILE, or when FILE is -,
       read standard input.  A word is a non-zero-length sequence of characters delimited by white space.  The options below may be used to select
       which counts are printed, always in the following order: newline, word, character, byte, maximum line length.

       -c, --bytes
	      print the byte counts

       -m, --chars
	      print the character counts

       -l, --lines
	      print the newline counts

       --files0-from=F
	      read input from the files specified by NUL-terminated names in file F; If F is - then read names from standard input

       -L, --max-line-length
	      print the length of the longest line

       -w, --words
	      print the word counts

       --help display this help and exit

       --version
	      output version information and exit

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AUTHOR

       Written by Paul Rubin and David MacKenzie.

COPYRIGHT

       Copyright (C) 2013 Free Software Foundation, Inc.  License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
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SEE ALSO

       The full documentation for wc is maintained as a Texinfo manual.  If the info and wc programs are properly installed at your site, the com-
       mand

	      info coreutils 'wc invocation'

       should give you access to the complete manual.

GNU coreutils 8.22						     June 2014								     WC(1)
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