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A question about if statement

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# 8  
Old 12-05-2011
Thank you very much for your replies.
What I want to do is: I will run a program and write the result of its execution to the file "result.txt". Then I grep in the output file, if it contains the phrase "VERIFICATION SUCCESSFUL", it means the verification process is successful.

Then I need to run a complicated multi-level if statement whose conditions are the verification result. Something like this:
Code:
pattern()
{
     if [ verify 'condition1' ] then

         if [ verify 'condition2' ] then

             echo debug 1

         else

             echo debug 2

         fi

     elif [ verify 'condition3' ] then

         echo debug 3

     else

         echo debug 4

     fi

}

I can test the exist of the phrase by this way:
Code:
 if grep -q 'VERIFICATION SUCCESSFUL' result.txt

But how can I make a wrapper of it, to use the verify function as above?
Last edited by Scott; 12-05-2011 at 04:58 AM.. Reason: Code tags, please...
# 9  
Old 12-05-2011
You're rather ambiguous about this verify() function. It takes an argument? I don't see where...

'if' takes a command as an argument, [ is a command, grep is also a command. A function by default returns the exit code of it's last command...

Code:
verify() {
    local condition=$1

    # do something with $condition
    grep -q 'SUCCESS' results.txt
}

if verify 'condition1'; then
   whatever
elif verify 'condition2'; then
   something else...
else
   i don't know ...
fi

This User Gave Thanks to neutronscott For This Post:
Dark2Bright
# 10  
Old 12-05-2011
Quote:
Originally Posted by neutronscott
You're rather ambiguous about this verify() function. It takes an argument? I don't see where...

'if' takes a command as an argument, [ is a command, grep is also a command. A function by default returns the exit code of it's last command...

Code:
verify() {
    local condition=$1

    # do something with $condition
    grep -q 'SUCCESS' results.txt
}

if verify 'condition1'; then
   whatever
elif verify 'condition2'; then
   something else...
else
   i don't know ...
fi

Yes, it worked for me. Don't know how to thank you enough.
I didn't know that [] is also a command, i thought that it just like "if (condition)" in C.
Just one last question, if [ is a command, what is its meaning in this statement if [ $i -gt $j ]
# 11  
Old 12-05-2011
[ is a command, but in bash it's a shell builtin.

Code:
$ ls -l /usr/bin/[
-rwxr-xr-x 1 root root 28300 Apr 28  2010 /usr/bin/[

Quote:
Just one last question, if [ is a command, what is its meaning in this statement if [ $i -gt $j ]
test $i greater than $j. So that exit is 0 (success) if $i > $j, and non-zero otherwise.

Since you're using bash, it's worth noting that [[ is a better and preferred test. Quoting isn't needed, and it offers more (regex matching)..

Code:
# using "[":
if [ "$i" -gt "$j" ]; then
# using bash's "[["
if [[ $i -gt $j ]]; then
# using arithmetic
if ((i > j)); then

This User Gave Thanks to neutronscott For This Post:
Dark2Bright
# 12  
Old 12-05-2011
I understand. Thanks again.
# 13  
Old 12-06-2011
After if it's always command in shells: [, [[, (( are only some commands.
Code:
if commandline 
then # exit status 0
   :
else # exit status != 0
  :
fi

[ and test are same command, usually builtin command today. If you use command [, then the last argument must be ] = line looks like as in some programming languages.
Code:
grep "some" file >/dev/null 2>&1
stat=$?
if [ $stat = 0 ] ; then
     echo founded
else
    echo not
fi

Same result [ and test are same command
Code:
grep "some" file >/dev/null 2>&1
stat=$?
if  test $stat = 0 ; then
     echo founded
else
    echo not
fi

Same result, grep output is not needed => output to the /dev/null
Code:
if grep "some" file >/dev/null 2>&1 ; then
     echo founded
else
    echo not
fi

Same result
Code:
grep "some" file >/dev/null 2>&1  && echo founded || echo not

This User Gave Thanks to kshji For This Post:
Dark2Bright
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