topic Re: Incremental by 1 in the for loop in Operating System - HP-UX

Incremental by 1 in the for loop

wojtek75 — Wed, 08 Apr 2009 13:51:21 GMT

He,

it is easy for 3 elements:
for i in 1 2 3; do echo $i; done

How I can make it for 100 elements without listing all the numbers? Thanks in advance.

Re: Incremental by 1 in the for loop

James R. Ferguson — Wed, 08 Apr 2009 13:55:19 GMT

Hi:

#!/usr/bin/sh
typeset -i N=1
while (( N <= 100 ))
do
echo ${N}
N=$N+1
done

Regards!

...JRF...

Re: Incremental by 1 in the for loop

wojtek75 — Wed, 08 Apr 2009 13:59:39 GMT

Thanks, any ideas with 'for' loop?

Re: Incremental by 1 in the for loop

James R. Ferguson — Wed, 08 Apr 2009 14:05:24 GMT

Hi (again):

> Thanks, any ideas with 'for' loop?

No, not with the shell.

Regards!

...JRF...

Re: Incremental by 1 in the for loop

Mel Burslan — Wed, 08 Apr 2009 14:27:33 GMT

Together with agreeing JRF's "not with `for`" view, I am under the impression that you are trying to do something with a vast number of files or similar. If this is the case, for directive can work for you, if you can come up with a regex (regular expression), covering all of these files. For example:

for file in `ls -1 /home/mydir/data/IN*`
do
echo ${file}
cp ${file} /home/mydir/archive
done

if you are dealing with sequential numbering and do not want to write numbers one-by-one manually, you have no other choice than using the while construct, as 'for' directive does not work the same way in UNIX shells as it does on high level languages as BASIC.

Hope this helps

Re: Incremental by 1 in the for loop

Steven Schweda — Wed, 08 Apr 2009 14:30:40 GMT

> Thanks, any ideas with 'for' loop?

No matter how much you love your hammer,
sometimes a screwdriver is a better tool for
the job.

Perhaps you could "echo ${N}" into a
variable, and use that result in a "for"
statement. (But that wouldn't make it the
right thing to do.)

Re: Incremental by 1 in the for loop

James R. Ferguson — Wed, 08 Apr 2009 15:12:17 GMT

Hi (again):

Steven makes a good point. If you want a better "hammer" you need to look elsewhere.

The 'sh-posix' manpages make it clear that a 'for' loop is the interation over a list unlike C's 'for' loop or even Perl's variations. In Perl, for example, I could write:

# perl -le 'for ($n=1;$n<=100;$n++) {print $n}'

...using the C-syntax for 'for'. However, I wouldn't do that when I could do:

# perl -le 'print for 1..100'

It's all about TIMTOWDI --- screwdrivers and hammers; but if all you have is a hammer, you have to use it as intended :-)

Regards!

...JRF...

Re: Increment by 1 in the for loop

Dennis Handly — Mon, 28 May 2012 08:27:37 GMT

>JRF: N=$N+1

A typo, it should be: (( N = N + 1 )) or (( N += 1 ))

(Actually that initial assignment does work but you can't have spaces.)

Re: Incremental by 1 in the for loop

Arturo Galbiati — Thu, 09 Apr 2009 05:56:48 GMT

Hi,
to generate a range of
numbers for further use within a command pipe or
shell script. This can be done with some simple
sh-code:

------------------------ CUT HERE ------------------

#! /bin/sh

# range - Generate of numbers.

lo=$1
hi=$2

while [ $lo -le $hi ]
do
echo -n $lo " "
lo=`expr $lo + 1`
done

------------------------ CUT HERE ------------------

It can now be used a way like:

for i in $(range 1 100); do ; done

HTH,
Art

Re: Incremental by 1 in the for loop

Frank de Vries — Thu, 09 Apr 2009 07:20:32 GMT

To my mind it can be done.

You generate the numbers in a file with
a while loop (see above), but output >$TMPFILE

and then in your forloop you do

for i in $(cat $TIMPFILE)
do
typeset -i count
print $count
count=count+1
done

Re: Increment by 1 in the for loop

Dennis Handly — Mon, 28 May 2012 08:25:05 GMT

>Frank: To my mind it can be done.

Though in efficient, you could fix it as:
typeset -i count
for i in $(< $TMPFILE); do
print $count
(( count+=1 ))
done

Re: Incremental by 1 in the for loop

James R. Ferguson — Thu, 09 Apr 2009 11:21:15 GMT

Hi (again):

As an encompassing remark, efficiency may not seem very measureable in small scripts operating on minute amounts of data. Good practices there, however, lead to fast, scalable code that "thinks green".

Using 'typeset -i' creates an integer variable that makes arithmetic faster.

Using '(( N = N + 1 ))' to increment an integer by one lets the shell do the work without spawning a completely different process as when 'N=`expr $N + 1`' is used.

Writing 'X=$(< $FILE)' instead of 'X=$(cat $FILE)' is a subtle but faster optimization for capturing the contents of a file into a variable.

While, TMTOWTDI, there are fast and there are slow(er) paths to travel.

Regards!

...JRF...

Re: Incremental by 1 in the for loop

Viktor Balogh — Thu, 09 Apr 2009 11:27:13 GMT

just a thought:

if it would be a linux server you could just simply use the 'seq' command like this:

for i in $(seq 1000)
do
echo "This is the $i line."
done

Re: Incremental by 1 in the for loop

Raynald Boucher — Thu, 09 Apr 2009 11:50:15 GMT

James,
Where can I find the documentation for the "typeset" command.

I looked in man pages, typed "typeset -?" and "-h", looked in several books but still can't find it.

RayB

Re: Incremental by 1 in the for loop

James R. Ferguson — Thu, 09 Apr 2009 16:25:17 GMT

Hi (again):

> James, Where can I find the documentation for the "typeset" command.

The 'typeset' command is documented in shell manpages:

http://docs.hp.com/en/B3921-60631/sh-posix.1.html

Regards!

...JRF...

Re: Incremental by 1 in the for loop

Dennis Handly — Fri, 10 Apr 2009 02:40:35 GMT

>JRF: Using '(( N = N + 1 ))' to increment an integer by one lets the shell do the work

Another reason to use ksh's (( )) is that it supports 64 bit integers and expr(1) only 32.

Re: Incremental by 1 in the for loop

Arturo Galbiati — Fri, 10 Apr 2009 06:31:48 GMT

Hi,
revised to be more efficient:
------------------------ CUT HERE ------------------
#!/bin/sh
# range - Generate of numbers.
typeset -i lo=$1
typeset -1 hi=$2
while [ $lo -le $hi ]
do
echo -n $lo " "
(( lo=lo+1 ))
done
------------------------ CUT HERE ------------------

HTH,
Art