for loop syntax trouble


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# 1  
for loop syntax trouble

i don't get what's wrong here. i'm writing a shell script that takes 1 argument (a number) from the command-line, but it's throwing an error:
Syntax error: Bad for loop variable

doesn't make much sense
Code:
for ((  i = 1;  i = ${1};  i++  )) # error points to this line everytime
do
    echo "Welcome $i times"
done

i've tried changing it several times, but it always throws the same error. what's the problem with it?

Last edited by visitorQ; 04-12-2008 at 01:40 PM..
# 2  
What syntax is that supposed to be? Even in C shell syntax this doesn't make much sense.

The shell doesn't have i++ or that particular variant of for loop syntax. You can construct a loop but the syntax is more like

Code:
i=1
while [ $i != $1 ]; do
  echo Welcome $i times
  i=`expr $i + 1`
done

Modern shells have more support for arithmetic, but this should work even in good ole Bourne Shell Classic.
# 3  
thank you so much for the quick reply buddy! i ended up doing this which worked just fine:
Code:
#!/bin/sh

for i in `seq 1 ${1}`
do
    echo "Welcome ${i} times";
done

but your code seems to be cleaner and make more sense, so i'll adopt that method instead.
# 4  
That loop structure is a prefectly valid construct in bash, ksh93, jsh or zsh however the logic is broken.

a single = is used as an assignment.
a double = ( == ) is used as comparison.

If you want to print $i times the logic doing the test in the loop should be <=, or !=.

Code:
for (( i = 1 ; i <= ${1} ; i++ ))

# 5  
This for syntax is valid with bash (the equal compate operator is == not =):
Code:
for ((  i = 1;  i <= ${1};  i++  )) 
do
    echo "Welcome $i times"
done

With sh or ksh, you must use a while statement.

Jean-Pierre.
# 6  
wow thanks for all the replies! i learned a lot!
# 7  
Hi.
Quote:
Originally Posted by aigles
... With sh or ksh, you must use a while statement.

Jean-Pierre.
This version of ksh accepts the extended for syntax:
Code:
#!/bin/ksh

# @(#) s1       Demonstrate for loop in ksh.

echo
echo "(Versions displayed with local utility \"version\")"
version >/dev/null 2>&1 && version =o $(_eat $0 $1)

N=3

echo
for ((  i = 1;  i <= ${N};  i++  ))
do
    echo "Welcome $i times"
done

exit $?

producing:
Code:
$ ./s1

(Versions displayed with local utility "version")
Linux 2.6.24-1-686
ksh 93s+

Welcome 1 times
Welcome 2 times
Welcome 3 times

I will say I was surprised to find this AT&T version of ksh in Debian Lenny rather than the previous pdksh, but it makes life easier in some situations. Solaris 10 still has pdksh as the default ksh [edit: this is not true, see post below] ... cheers, drl

Last edited by drl; 04-12-2008 at 07:06 PM.. Reason: Point out error in assertion for Solaris 10.
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For loops in C use the familiar syntax of placing the initialization, continuation condition, and interpretation on the same line as the keyword for.
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