Shell Programming and Scripting

I have a user defined configuration file, which could contain the following type of entries:

directory_001=/a/directory/structure
pattern_001=fred*
pattern_002=*

I have a script which reads the file generically which will loop round

loop 1
genvar=”directory”
iteration=”001”

eval varcontents=”\$genvar”_”$iteration”

expected results varcontents=/a/directory/structure

loop 2
genvar=”pattern”
iteration=”001”

eval varcontents=”\$genvar”_”$iteration”

expected results varcontents=”fred*”

The above appears to work fine, however, the problem arises with loop 3

loop3
genvar=”pattern”
iteration=”002”

eval varcontents=”\$genvar”_”$iteration”

expected results varcontents=”*”
actual results are an error pattern_002: parameter not set

I realise what is happening and can resolve the problem by using pattern_002=\* in the config file. The problem is that the file is user created and it may be that someone will forget the backslash before the *.

Can someone suggest a way to resolve this so that a * without a backslash can be used in the configuration file please?

Many thanks for your help,
Helen

To preserve characters with a special meaning to the shell you have to protect them - usually by quoting them. Without knowing your actual code: if using \* instead of * solves your problem chances are that somewhere in your script you use your variable containing the asterisk without quoting: $variable instead of "$variable".

I suggest you look carefully through your code for such occasions, it might very well solve your problem.

Hope this helps.

bakunin

You could set -o noglob before the eval and then set +o noglob after.

Hi Bakunin,

The issue, I believe, is the eval statement. However I need to use the eval statement to get the contents of the variable.

Cheers
Helen

Hi Grasper,

I tried that but it gets the same error. I'm not sure what noglob does.

Out of interest it HPUX 11.00 and Korn shell.

Cheers
Helen

Apologies, I may have been a bit hasty in suggesting that in that way. noglob prevents wildcard characters from being expanded.

I don't know exactly how you'll be extracting your variables from the file or using them in your script, but here's a bit of code which uses eval in a similar way to the way you seem to need it and allows the asterisk character to be preserved:-

#!/bin/ksh

set -o noglob
pattern_002=*
set +o noglob
echo "PATTERN $pattern_002"

genvar="pattern"
iteration="002"

varc=$"$genvar"_"$iteration"
eval varcontents=$varc

set -o noglob
echo $varcontents
set +o noglob

When I run this I get the output:-

PATTERN *
PATTERN *
Hope that's of some use

Hi Helen,

the eval-statement will surely leave the asterisk unprotected. In this case the only way to deal with it is to escape it in the script itself:

'sed s/\*/\\&/g'

Hope this helps even better. ;-))

PS: "noglobber" or the equivalent parameter "-f" prevents filename substitution. The problem is that an "eval ..." might take precedence (i have never tested that).

bakunin