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Full Discussion: Editing file
Top Forums Shell Programming and Scripting Editing file Post 302137154 by AnswerGuy on Sunday 23rd of September 2007 03:55:40 AM
Old 09-23-2007
Lightbulb NUL terminate first field of each line?
Rahul,

It sounds like you're trying to NUL terminate the first (whitespace delimited) field (word) of each line in a text file.

That's a very odd request (because the ASCII NUL character is normally used to terminate strings ... but normally NOT embedded in text files ... so many tools that might be trying to read the file line by line would not handle the NUL character gracefully.

It's also possible that your shell or your copy of sed or whatever cannot handle this cleanly. So you might need to use GNU versions of these tools, or a copy of Perl or Python (or compile up a little utility in C, of course).

The most obvious attempt in plain bash would be:

Code:
#!/bin/bash
while IFS="" read line; do 
    set -- $line
    first_word="$1"
    shift
    echo -e "$firstword\000$*"
   done

This is written as a filter so you pipe you file through it. To verify that it's doing what you want you can pipe the output further through a command like cat -A or od -x to be sure it shows the NUL characters where you want them.

That might have some odd artifacts (due to the way that each line is parsed by the set -- command). This following one-liner works in two stages, using sed the first space on each line to a character "177" (octal) --- hex 0x7F, a.k.a. the "DEL" character; and then using the tr command to change that into an ASCII NUL:

Code:
sed -e 's/ /'$(echo -ne '\177')'/' /tmp/foo | tr '\177' '\00'  | cat -A

This assumes that the original file has no ASCII DEL character that you care about preserving ... and the example shows a cat -A just for your convenience. You'd replace that with an appropriate redirection to save your output.

JimD (former Linux Gazette AnswerGuy)
 

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LEARN ABOUT SUNOS

tr

tr(1B)						     SunOS/BSD Compatibility Package Commands						    tr(1B)

NAME

       tr - translate characters

SYNOPSIS

       /usr/ucb/tr [-cds] [ string1 [string2]]

DESCRIPTION

       The tr utility copies the standard input to the standard output with substitution or deletion of selected characters. The arguments string1
       and string2 are considered sets of characters. Any input character found in string1 is mapped into the character in the corresponding posi-
       tion within string2. When string2 is short, it is padded to the length of string1 by duplicating its last character.

       In either string the notation:

	      a-b

       denotes	a  range  of  characters from a to b in increasing ASCII order. The character , followed by 1, 2 or 3 octal digits stands for the
       character whose ASCII code is given by those digits. As with the shell, the escape character , followed by any	other  character,  escapes
       any special meaning for that character.

OPTIONS

       Any combination of the options -c, -d, or -s may be used:

       -c	Complement  the  set  of  characters  in  string1 with respect to the universe of characters whose ASCII codes are 01 through 0377
		octal.

       -d	Delete all input characters in string1.

       -s	Squeeze all strings of repeated output characters that are in string2 to single characters.

EXAMPLES

       Example 1: Creating a list of all the words in a filename

       The following example creates a list of all the words in filename1, one per line, in filename2, where a word  is  taken	to  be	a  maximal
       string of alphabetics. The second string is quoted to protect `' from the shell. 012 is the ASCII code for NEWLINE.

       example% tr -cs A-Za-z '12' <filename1>filename2

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWscpu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       ed(1), ascii(5), attributes(5)

NOTES

       Will not handle ASCII NUL in string1 or string2. tr always deletes NUL from input.

SunOS 5.10							    26 Sep 1992 							    tr(1B)
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