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Full Discussion: How to replace a whitespace with line break?
Top Forums Shell Programming and Scripting How to replace a whitespace with line break? Post 302894090 by alister on Monday 24th of March 2014 02:56:43 AM
Old 03-24-2014
Quote:
Originally Posted by Lucas_0418
Just do some check for the arguments
Code:
$ cat test.sh
#!/bin/sh
if [ $# -eq 0 ];then
    while read -r line
    do
        case "$line" in
            quit|Quit)
                exit 0;;
            *)
                echo "$line"|tr '[[:space:]]' '\n';;
        esac
    done
else
    for i in $@
    do
        if [ "$i" = '-' ];then
            trap '"break"' INT
            while read -r line
            do
                echo "$line"|tr '[[:space:]]' '\n'
            done
        else
            while read -r line
            do
                echo "$line"|tr '[[:space:]]' '\n'
            done<"$i"
        fi
    done
fi

cheer up.
The while-read loops are unnecessary. They may also be buggy, since the goal is to convert whitespace and with the default value of IFS, the shell will discard leading and trailing whitespace before assigning a value to $line.

The echo statements are also unnecessary and are also problematic, because, if the line that's read looks like a command line option, it may alter the value of $line or even generate a syntax error. When it's necessary (here it's not), the best way to echo arbitrary text is to use printf '%s\n' "$line".

I don't see the point of the trap. - means stdin; stdin may not be a terminal. If the trap is meant as a way to give a human user a way to abort and continue to the next file in the for-loop list, it's redundant; ^D (control-d) will do the job by sending EOF (end-of-file).

The same goes for the quit|QUIT check in the case-statement. stdin may not be a terminal, even if there is no file argument.

Finally, forking a shell and exec'ing an instance of tr for every line read is very inefficient.

The simplest, most efficient solution is to redirect stdin using exec before invoking tr.

Regards,
Alister
Last edited by alister; 03-24-2014 at 04:04 AM..
 

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LEARN ABOUT OSF1

line

line(1) 						      General Commands Manual							   line(1)

NAME

       line - Reads one line from standard input

SYNOPSIS

       line

STANDARDS

       Interfaces documented on this reference page conform to industry standards as follows:

       line:  XCU5.0

       Refer to the standards(5) reference page for more information about industry standards and associated tags.

OPTIONS

       None

DESCRIPTION

       The  line  command  copies one line, up to and including a newline, from standard input and writes it to standard output.  Use this command
       within a shell command file to read from your terminal.	The line command always writes at least a newline character.

NOTES

       The line utility has no internationalization features and is marked LEGACY in XCU Issue 5. Use the read utility instead.

EXIT STATUS

       Success.  End-of-File.

EXAMPLES

       To read a line from the keyboard and append it to a file, enter: echo 'Enter comments for the log:' echo ': c' line >>log

       This shell procedure displays the message: Enter comments for the log:

       It then reads a line of text from the keyboard and adds it to the end of the file log.  The echo  ':  c'  command  displays  a	:  (colon)
       prompt.	See the echo command for information about the c escape sequence.

SEE ALSO

       Commands:  echo(1), ksh(1), read(1), Bourne shell sh(1b), POSIX shell sh(1p)

       Functions:  read(2)

       Standards:  standards(5)

																	   line(1)
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