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If else - grep a string in a file

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# 1  
Old 04-28-2010
If else - grep a string in a file
Hi all,

I would want to recieve notification only if there are sessions block in our databases.

This is my script, but it's not working. No matter what is the contents in the $OUTFILE, I get emails.

Code:
/usr/bin/cat $OUTFILE | read selected

if [ "$selected" = "no rows selected" ]
then
  echo "No session is blocked"
else
  cat $OUTFILE | mailx -s "[TESTING]Blocking sessions in $ORACLE_SID" $DBA
fi
exit


Any suggestions? Thanks!
Last edited by Franklin52; 04-28-2010 at 02:57 AM.. Reason: Please use code tags!
# 2  
Old 04-28-2010
The way which you read the file content into variable is the issue.

You can do it as,

Code:
selected=`cat $OUTFILE`

Try debugging, like echo the variable after reading.
# 3  
Old 04-28-2010
Code:
if grep "no rows selected" $OUTFILE
then
   cat $OUTFILE | mailx -s "[TESTING]Blocking sessions in $ORACLE_SID" $DBA
else
   echo "No session is blocked"
fi

# 4  
Old 04-28-2010
Quote:
Originally Posted by rdcwayx
Code:
if grep "no rows selected" $OUTFILE
then
   cat $OUTFILE | mailx -s "[TESTING]Blocking sessions in $ORACLE_SID" $DBA
else
   echo "No session is blocked"
fi

I've never seen an if formatted quite like that. I tried it out, and I'm not sure I understand why you would want to do that. Wouldn't the grep display to the screen when you ran the script? And wouldn't that be a pain?

Code:
(02:23:01\[D@DeCoBox15)
[~]$ cat animals
cat
dog
hippo

(02:23:07\[D@DeCoBox15)
[~]$ cat p
#!/bin/bash

file=animals
if grep "$1" $file
then
echo "there is a $1"
else
echo "there is no $1"
fi


(02:23:10\[D@DeCoBox15)
[~]$ ./p dog
dog
there is a dog

(02:23:18\[D@DeCoBox15)
[~]$ ./p snake
there is no snake

Wouldn't it be better to just check that the grep returns something?

Code:
(02:26:07\[D@DeCoBox15)
[~]$ cat o
#!/bin/bash

file=animals
if [[ -n $(grep "$1" $file) ]];then
echo "there is a $1"
else
echo "there is no $1"
fi


(02:26:10\[D@DeCoBox15)
[~]$ ./o cat
there is a cat

(02:26:14\[D@DeCoBox15)
[~]$ ./o snake
there is no snake

# 5  
Old 05-10-2010
I understand your meaning, it is good to use
Code:
[[ -n $(grep "$1" $file) ]]

but I can also avoid to display the grep output by below code.

Code:
#!/bin/bash

file=animals
if grep "$1" $file  > /dev/null 2>&1
then
  echo "there is a $1"
else
  echo "there is no $1"
fi

# 6  
Old 05-10-2010
If syntax is
Code:
if commandline_exit_code_is_0
then
    do_some
fi

After if is any command line and after executing, shell test the exit code of the command line.

Those people who has used programming language, forget your if and learn shell if, it's little different. [, [[, grep, ((, rm, cp, ... all those are commands even some of those look more ...
# 7  
Old 05-11-2010
Quote:
Originally Posted by rdcwayx
I understand your meaning, it is good to use
Code:
[[ -n $(grep "$1" $file) ]]

but I can also avoid to display the grep output by below code.

Code:
#!/bin/bash

file=animals
if grep "$1" $file  > /dev/null 2>&1
then
  echo "there is a $1"
else
  echo "there is no $1"
fi

Well yeah, but if you were going to do that, you might as well say:

Code:
#!/bin/bash

file=animals
if grep -q "$1" $file  
then
  echo "there is a $1"
else
  echo "there is no $1"
fi

Of course now we're being pedantic...I just wanted to show off my recently discovered "quiet" switch for grep. But as kshji said, I hadn't considered that [[ is a command in of itself, and really you can get way with just if. That was the part I wasn't considering.
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