linux script

lewinmg · 04-05-2009, 03:45 PM

im not sure why this has been so hard to search for, but i've spent a good 2 hours searching for a simple anwser to this...maybe there isnt one?

im in linux shell trying to do a script that will simply convert a string to a number..

$vi test.script

A="1234"

but now i want A to be in Integer of 1234.

is this possible. I've seen so many example that dont apply to what im doing..any help would be appreciated...thanks.

-mark

i92guboj · 04-05-2009, 04:08 PM

I am not sure what exactly do you want to achieve. In bash everything is a string, there aren't any other data types. What is exactly what you need to do?

Robhogg · 04-05-2009, 04:11 PM

Darn! Beaten to it

Like Perl, PHP, JavaScript and similar languages, if a value can be interpreted as a number, then it will be treated as one when you try to use it as a number, and as a string when you try to use it as a string:

Code:

rob:~$ A="1629"
rob:~$ echo $A
1629
rob:~$ A=$(($A + 1))
rob:~$ echo $A
1630
rob:~$ A="${A} Revello Drive"
rob:~$ echo $A
1630 Revello Drive
rob:~$ A=$(($A + 1))
bash: 1630 Revello Drive + 1: syntax error in expression (error token is 
"Revello Drive + 1")
rob:~$

lewinmg · 04-05-2009, 04:47 PM

ok, so really, even if a = "1234" and i try to test it against a known integer like (b=1235) and use "-lt", it'll work ok? hmmm..i'll try that.

thanks so much....for some reason i thought i had to convert it to the same type...im so used to other languages needing to know the type, i never would have thought that would work..

i92guboj · 04-05-2009, 05:00 PM

Quote:

Originally Posted by lewinmg

ok, so really, even if a = "1234" and i try to test it against a known integer like (b=1235) and use "-lt", it'll work ok? hmmm..i'll try that.

thanks so much....for some reason i thought i had to convert it to the same type...im so used to other languages needing to know the type, i never would have thought that would work..

Yes. That's the way bash does it. It doesn't have any proper data type separation which can be a bit confusing at first. Some examples:

Code:

if [ "$A" -lt "$B" ]; then echo "$A is lesser than $B"; fi
if [ ! "$A" -lt "$B" ]; then echo "$A is not lesser than $B"; fi
if [ "$A" -ge "$B" ]; then echo "$A is greater than or equal to $B"; fi
if [ "$A" -eq "$B" ]; then echo "$A is equal to $B"; fi
if [ "$A" == "$B" ]; then echo "$A is equal to $B"; fi
if [ "$A" == "1024" ]; then echo "$A is equal to 1024"; fi

Robhogg · 04-05-2009, 05:08 PM

Actually, (perhaps because it doesn't understand the difference), there are different operators in the shell for numeric and string comparisons:

Code:

String                 Numeric
[ $var1 = $var2 ]      [ $var1 -eq $var2 ]
[ $var1 != $var2 ]     [ $var1 -ne $var2 ]
[ $var1 \> $var2 ]      [ $var1 -gt $var2 ]
[ $var1 \< $var2 ]      [ $var1 -lt $var2 ]

for example:
rob:~$ if [ '1234' \> '987' ]; then echo 'Higher!'; else echo 'Lower!'; fi
Lower!
rob:~$ if [ '1234' -gt '987' ]; then echo 'Higher!'; else echo 'Lower!'; fi
Higher!

See "Other Comparison Operators" for more.

i92guboj · 04-05-2009, 05:23 PM

Yes, there are different operators, but that doesn't make the data typing of bash any more solid. It only applies to a conceptual level, but for bash everything is a string.