Incremental by 1 in the for loop

[wojtek75]

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.

[James R. Ferguson · Accepted solution]

Hi:

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

Regards!

...JRF...

[wojtek75]

Thanks, any ideas with 'for' loop?

[James R. Ferguson]

Hi (again):

> Thanks, any ideas with 'for' loop?

No, not with the shell.

Regards!

...JRF...

[Mel Burslan]

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

[Steven Schweda]

> 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.)

[James R. Ferguson]

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...

[Dennis Handly]

>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.)

[Arturo Galbiati]

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

[Frank de Vries]

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

[Dennis Handly]

>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

[James R. Ferguson]

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...

[Viktor Balogh]

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

[Raynald Boucher]

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

[James R. Ferguson]

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...

[Dennis Handly]

>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.

[Arturo Galbiati]

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