syntax of for loop in linux shell scripting
Solution 1
You probably run it with sh
, not bash
. Try bash test1.sh
, or ./test1.sh
if it's executable, but not sh test1.sh
.
Solution 2
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)
Solution 3
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
Solution 4
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 containbash
).
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.
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mkab
Updated on October 19, 2020Comments
-
mkab over 3 years
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 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?
-
Robin Green about 13 yearsI don't get the same error as you for that - I get unexpected end of file. Anyway, you have a missing semicolon.
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karlphillip about 13 yearsThat works for me. You probably have a weird character hidden in the text.
-
Costi Ciudatu about 13 yearsFor bash the syntax seems fine. Can you try to make sure you're running the right shell ?
ls -l /bin/bash
, maybe ? -
Amir Afghani about 13 yearsThis works for me when you put the done statement on its own line.
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mkab about 13 yearsI ran it using sh instead of bash. Works fine in bash. Thanks everyone.
-
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Jim Garrison about 13 yearsWorks fine in bash as currently displayed in the post
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mkab about 13 yearsKrelin: You are right. I ran it using sh instead of bash or "./". It works well now. Thanks
-
Ankur Agarwal about 13 yearsYes works fine in bash. Make sh point to bash ( symbolic link) !