shell script variable use

Question

I'll get to the meat and bones:

MY_VAR=6
until [$MY_VAR = 0]
do
dir/dir_$MY_VAR.log
ps | grep "NAME_$MY_VAR.ksh"
check some things
if [results = ok]
echo "program $MY_VAR sucessful"
else
echo "program $MY_VAR failure"
MY_VAR = `expr $MY_VAR - 1`
done

Now I am getting the following errors MY_VAR not found and [6: not found, so I'm assuming a rather noobish mistake. I feel the logic is sound enough just a simple syntax error I am making somewhere by the looks of the two errors I think it could be in the declaration.

Dennis Williamson · Accepted Answer · 2011-01-07 15:45:56Z

3

You need to have a space after [ and before ] since [ is actually a command and not a delimiter.

Here is your script re-written in Bash (or ksh):

my_var=6
until ((my_var == 0))
do
    dir/dir_$my_var.log    # I have no idea what this is supposed to be
    ps | grep "NAME_$my_var.ksh"
    # check some things
    if [[ $results = ok ]]
    then
        echo "program $my_var successful"
    else
        echo "program $my_var failure"
        ((my_var--))
    fi
done

However:

for my_var in {6..1}
do
    dir/dir_$my_var.log    # I have no idea what this is supposed to be
    ps | grep "NAME_$my_var.ksh"
    # check some things
    if [[ $results = ok ]]
    then
        echo "program $my_var successful"
    else
        echo "program $my_var failure"
    fi
done

edited Jan 7, 2011 at 15:45

answered Jan 6, 2011 at 17:09

Dennis Williamson

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3 Comments

Jewsef Over a year ago

I get the error MY_VAR--: more tokens expected, could you elaborate on your solution such as the use of (()) and [[]]

Dennis Williamson Over a year ago

@Jewsef: Using which shell and on which line of which version of the scripts from my answer? One thing to note, I had changed the case of the variable name, but I did so inconsistently. That may have caused some trouble. Sorry about that - I've fixed it. In Bash and ksh double square brackets enable some additional capabilities. Using double parentheses for numeric comparisons allows you to use == and >, for example, instead of the ugly -eq and -gt. It also allows you to do arithmetic operations such as the decrement ((my_var--)) shown.

Dennis Williamson Over a year ago

@Jewsef: I just noticed that the script in your question is missing the fi to close the if. I copied your script into my answer and missed fixing that (now fixed). That could be the source of your error.

camh · Accepted Answer · 2011-01-06 21:44:19Z

0

Your two errors are caused by:

until [$MY_VAR = 0]
MY_VAR = $(expr $MY_VAR - 1)

[I've used $() instead of backticks because I couldn't get backticks into the code section]

The first problem is the lack of spaces around the square brackets - on both ends. The shell is looking for the command [6 (after expanding $MY_VAR), instead of [ (have a look at /usr/bin/[ - it's actually a program). You should also use -eq to do numeric comparisons. = should work ok here, but leading zeros can break a string comparison where a numeric comparison would work:

until [ "$MY_VAR" -eq 0 ]

The second problem is you have spaces in your variable assignment. When you write MY_VAR = ... the shell is looking for the command MY_VAR. Instead write it as:

MY_VAR=`expr $MY_VAR - 1`

These answers directly answer your questions, but you should study Dennis Williamson's answer for better ways to do these things.

answered Jan 6, 2011 at 21:44

camh

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1 Comment

Dennis Williamson Over a year ago

It's true that [ exists as /usr/bin/[, but it's a shell builtin, too, and as such has precedence. Be careful of relying on the leading zero behavior, [ 008 -eq 8 ] works, but [[ 008 -eq 8 ]] gives a value too great for base error. Backticks should be avoided anyway, use of $() is preferred.

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