topic while read loop help in Operating System - HP-UX

while read loop help

Avinash Agarkar — Wed, 03 Feb 2010 10:37:07 GMT

I have written a script using a loop but when I execute it using while read, it only read the first line and quits the loop after processing the first line. If I change it from (while read) to (for i in) it reads all the lines and finishes the loop?

any advice will be appreciated

Thanks,
Avinash

Re: while read loop help

Michal Kapalka (mikap) — Wed, 03 Feb 2010 12:19:40 GMT

hi,

the bets way is to send the loop that you are using.

mikap

Re: while read loop help

Dennis Handly — Thu, 04 Feb 2010 11:49:40 GMT

This is the wrong forum for scripting.
What OS and shell are you using?

Re: while read loop help

James R. Ferguson — Thu, 04 Feb 2010 14:38:34 GMT

Hi:

I would urge you to *post* your code. I suspect that you need two file descriptors --- one for the 'read' loop and another for the process you want to execute. If an 'ssh' or 'remsh' is called within the loop you will likely need to add the '-n' option to it.

Regards!

...JRF...

Re: while read loop help

Matti_Kurkela — Thu, 04 Feb 2010 14:57:26 GMT

Most likely you haven't noticed that the input/output redirection works a bit oddly in loop structures.

Wrong:

#!/bin/sh
# this reads only the first line
while read foo < inputfile.txt
do
echo "$foo"
done

Right:

#!/bin/sh
# this processes all lines in the file
while read foo
do
echo "$foo"
done < inputfile.txt

The "for i in $(cat inputfile.txt)" style loop is not suitable for files longer than the maximum command line length (8 KiB or so). If the file is longer than that, the script dies with "Command line too long" or equivalent error message.

With smaller files, it might work... but not the same as the "while read" loop: $i will iterate over the content of the input file, but one _word_ at a time, not one _line_ at a time.

MK

Re: while read loop help

Michael Steele_2 — Fri, 05 Feb 2010 00:43:33 GMT

HI

cat file | while read a (* or, number of words per line, a b c d e *)
do

echo $a (* whole line *)

done

Re: while read loop help

Sagar Sirdesai — Fri, 05 Feb 2010 04:23:37 GMT

Hi Avinash,
Please post the code which would help.

Sagar