topic Re: Question about variables in script in Operating System - HP-UX

Question about variables in script

Artyom Voronchihin — Fri, 04 Apr 2003 08:26:23 GMT

Hello.
1. How can i check if variable exist or not in sh ? (I know how to do it in csh) E.G.
if [ $VAR not exist ]; then
VAR=$(expr $VAR + 1)
export VAR
else
VAR=0
export VAR
fi

2. What is the best syntax for arithmetic operations like VAR=$(expr $VAR + 1) in sh? I don't want to use expr command, i'd like something like VAR++ in C language.

Re: Question about variables in script

H.Merijn Brand (procura — Fri, 04 Apr 2003 08:42:44 GMT

export VAR=`expr ${VAR:-0} + 1`

your logic is rather strange. If *not* defined increment, else set to 0

Enjoy, have FUN! H.Merijn

Re: Question about variables in script

Stefan Farrelly — Fri, 04 Apr 2003 08:45:18 GMT

1. To check if a variable exists;

[ -n "${:-}" ] && echo exists

replace for the variable name to check.

2. let =$+1

Re: Question about variables in script

Artyom Voronchihin — Fri, 04 Apr 2003 08:49:54 GMT

Ooooops ! Mixed up sections. Correct would be
if [ $VAR not exist ]; then
VAR=0
export VAR
else
VAR=$(expr $VAR + 1)
export VAR
fi

Re: Question about variables in script

Steve Steel — Fri, 04 Apr 2003 08:49:56 GMT

Hi

Use the -z option as shown in man test
for an existing variable.

if [ -z "$var" ]
then
echo not set
fi

See typeset -i in sh man

typeset -i x=1
x=$x+1

Steve Steel

Re: Question about variables in script

Dietmar Konermann — Fri, 04 Apr 2003 08:51:02 GMT

1)

if [[ -n ${VAR:-} ]]; then
((VAR+=1))
else
VAR=0
fi
export VAR

2)

((VAR+=1)) -or-
((VAR=VAR+1)) -or-
VAR=$((VAR+1))
...

Best regards...
Dietmar.