syntax of for loop in linux shell scripting

I have a problem implementing a for loop. I get this error when I execute my script

test1.sh: 2: Syntax error: Bad for loop variable

I don't 开发者_如何学编程understand this error.

This is my script

#!/bin/bash
for (( c=1; c<=5; c++ ))
do
echo "Welcome $c times..."
done

can any one tell me syntax for for loop in sh(in ubuntu it links to dash shell) shell in ubuntu?

You probably run it with sh, not bash. Try bash test1.sh, or ./test1.sh if it's executable, but not sh test1.sh.

A standard POSIX shell only accepts the syntax for varname in list

The C-like for-loop syntax for (( expr1; expr2; expr3 )) is a bashism.

You can get similar behavior in the standard POSIX shell using for c in $(seq 1 5)

What does

ls -l /bin/sh

give on your machine ?

Make sh a symbolic link to bash and then you can do sh ./test1.sh

Your shell script (as shown) runs in both Korn shell and Bash. Some thoughts:

• You might need a space after the shebang (#! /bin/bash and not #!/bin/bash). However, Dennis Ritchie had originally specified the space is optional. Besides, it isn't the error you get with Bourne shell (you get syntax error: '(' unexpected instead).
• Are you on a Windows system? Just a stab in the dark. This doesn't look like a Windows error.
• Is this Solaris or HP/UX system? They might not be running true versions of Bash, or maybe an older version. However, even the oldest version of Bash recognizes the for ((x;y;z)) construct.

Try this:

#! /bin/bash
set -vx
echo "Random = $RANDOM"   #Test for bash/Kornshell. Will be blank in other shells
echo \$BASH_VERSINFO[0] = ${BASH_VERSINFO[0]} #Should only work in BASH
echo \$BASH_VERSINFO[1] = ${BASH_VERSINFO[1]}
echo \$BASH_VERSINFO[2] = ${BASH_VERSINFO[2]}
echo \$BASH_VERSINFO[3] = ${BASH_VERSINFO[3]}
echo \$BASH_VERSINFO[4] = ${BASH_VERSINFO[4]}
echo \$BASH_VERSINFO[5] = ${BASH_VERSINFO[5]}
for ((c=0, c<=5, c++))
do
    echo "Welcome $c times"
done

• The set -xv will display all lines as they are executed.
• The $RANDOM should display a value if this is either BASH or Kornshell (your for loop will work in either one).
• The {$BASH_VERINFO[x]} should only be set if this is truly BASH. These aren't even set even if you run Korn shell after you're in BASH (unlike $SHELL which will still contain bash).

If the for loop still gives you trouble, just delete it. Somewhere in this script, we'll find out if you're really executing a bash shell or not.