Question about variables in script

[Artyom Voronchihin]

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.

[H.Merijn Brand (procura]

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

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

Enjoy, have FUN! H.Merijn

[Stefan Farrelly · Accepted solution]

1. To check if a variable exists;

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

replace for the variable name to check.

2. let =$+1

[Artyom Voronchihin]

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

[Steve Steel]

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

[Dietmar Konermann]

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.