Shell Programming and Scripting

Most shells won't hand integers that big.
In the case of a reversed date string a text compare should do.

Code:

#!/bin/ksh
currentfiledate="20090220080101"
reportfiledate="20090219231245"

if [ "${currentfiledate}" -gt "${reportfiledate}" ]
then
        echo "message"
fi

Hi,

Yes, the reversed date string compare works but the problem is that I have to add this logic to a bash script and the bash script will not handle "-gt" when comparing strings.

Thank you.

If there was a problem with the size of the integer, I should also have a problem changing their values, adding to them, But this code runs without error except when it is time to compare the variables.

#!/usr/local/bin/bash
currentfiledate=20090220080101
reportfiledate=20090219231245

currentfiledate=$(expr $currentfiledate + 1001)
reportfiledate=$(expr $reportfiledate + 1001)

echo $currentfiledate
echo $reportfiledate


if [ $currentfiledate -gt $reportfiledate ] ; then
echo -ne "!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! \n"
echo -ne "!! Running the load utility !! \n"
fi

Results from 'echo':
20090220081102
20090219232246


The smallest values I can use, when comparing without error, are between 1 and 999999999.

Thanks.

If there was a problem with the size of the integer, I should also have a problem changing their values, adding to them, But this code runs without error except when it is time to compare the variables.

#!/usr/local/bin/bash
currentfiledate=20090220080101
reportfiledate=20090219231245

currentfiledate=$(expr $currentfiledate + 1001)
reportfiledate=$(expr $reportfiledate + 1001)

echo $currentfiledate
echo $reportfiledate


if [ $currentfiledate -gt $reportfiledate ] ; then
echo -ne "!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! \n"
echo -ne "!! Running the load utility !! \n"
fi

Results from 'echo':
20090220081102
20090219232246


The smallest values I can use, when comparing without error, are between 1 and 999999999.

Thanks.

Try using the shell keyword [[ instead of the [ builtin:

Code:

[[ $currentfiledate -gt $reportfiledate ]]

Or better use the (( )) compound command:

Code:

(( "$currentfiledate" > "$reportfiledate" ))

If you're on Solaris, you may consider using the POSIX shell /usr/xpg4/bin/sh instead of this old version of bash,
notice that with that shell you should use the standard syntax: [ expression ].

Hi radoulov,

It works, I tried both ways with bash (I have no option on the shell selection) and they both worked.

Could you explain the difference between one set of square brackets vs 2 sets and how come I can use the ">" symbol as "greater than" in bash when using 2 sets of parentheses?

Thanks so much.

As far as the bash shell is concerned, you have:

1. The [ and the test builtin commands. In this context (after the [ and the test command) parameter expansion, word splitting and pathname expansion are performed[1]. So beware of the following situation when using the [ and the test commands:

- missing quotes
-- unset or null values:

Code:

$ unset var
$ [ $var -eq 1 ]
bash: [: -eq: unary operator expected

-- values containing IFS characters:

Code:

$ var="a b"
$ [ $var = "a b" ]
bash: [: too many arguments

-- pathname expansion:

Code:

$ touch x
$ var=\*
$ set -x
$ [ $var = "*" ]
+ '[' x = '*' ']'

- particular syntax for logical comparison:

Code:

$ [ value = value -a 1 -lt 2 ]&&echo true
true

2. The [[ non standard (ksh93, zsh and bash) compound command. Parameter expansion is performed inside [[ ]].
No word splitting and pathname expansion are performed[2]. Support more operators.
Consider the following:

- no need to quote unset variables or variables with null values or values containing IFS characters:

Code:

$ unset var
$ set -x              
$ [[ $var -eq value ]]
+ [[ '' -eq value ]]

Code:

$ var=a\ b
$ set -x
[[ $var == "a b" ]]
+ [[ a b == \a\ \b ]]

- new versions of bash support new operators:

Code:

$ var=abc              
[[ $var =~ ^a ]]&&echo OK
OK
$ echo "${BASH_REMATCH[@]}"
a

- readable operators for logical comparison:

Code:

$ [[ value == value && 2 < 1 ]]||echo false
false

3. The compound command ((expression)). From the manual pages for bash[3]:

Code:

$ unset a
$ ((++a))&&echo $a # version >= 3
1

And as far as your particular problem is concerned it seems like a limitation of the old version of bash you're using,
your code works with recent versions of the bash shell.

[1] For more details see the manual pages for bash, the section Shell Builtin Commands and CONDITIONAL EXPRESSIONS.
[2] For more details see the manual pages for bash, the section Compound Commands. Tilde expansion, arithmetic expansion, command substitution, process substitution, and quote removal are also performed.
[3] For more information see:

Code:

man bash|less -p^ARITHMETIC\ EVALUATION

Hope this helps.