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Searching for a specific string in a file

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# 1  
Old 06-27-2011
Searching for a specific string in a file
Hi

I am trying to search for a certain set of patterns within a file, and then perform other commands based on output.

testfile contents:
Code:
password    requisite     pam_cracklib.so lcredit=-1 ucredit=-1 ocredit=-1

script:
Code:
D="dcredit=-1"

if [ "cat testfile | grep -w "$D"" ]
then
echo $D exists
else
echo $D doesnt exist
fi

Tried executing, but it always outputs true regardless of whether $D is present or not.

Can someone please assist?

Thank you
# 2  
Old 06-27-2011
Try something like this:

Code:
if grep -q "$D" testfile 
then
   echo "there"
else
   echo "not there"
fi

You don't need to cat to grep; grep will read the file. You also don't want to test the output string like that. Test the return code from grep which will be 'success' if the pattern was matched.
This User Gave Thanks to agama For This Post:
bludhemn
# 3  
Old 06-27-2011
Try:
Code:
if grep -wq "$D" testfile
then
echo $D exists
else
echo $D doesnt exist
fi

This User Gave Thanks to yazu For This Post:
bludhemn
# 4  
Old 06-27-2011
Thank you for clearing this.

I tried with this
Code:
[ "`cat testfile | grep -w "$D"`" ]

and it worked too.

I am also trying at a later stage to get multiple grep conditions checked. Such as ,

Code:
if  grep -qw '"$D"|"$L"' testfile

Dont think im doing it right here. Does this need to be enclosed in [ ] ?

Thanks very much
# 5  
Old 06-27-2011
Quote:
Originally Posted by bludhemn
I am also trying at a later stage to get multiple grep conditions checked. Such as ,

Code:
if  grep -qw '"$D"|"$L"' testfile

Dont think im doing it right here. Does this need to be enclosed in [ ] ?

Thanks very much
You'll need to change things a wee bit.

First, I think, you'll need egrep if you are going to use 'pattern|pattern'. At least my version of grep won't do this, but egrep will.

Second, your variables won't expand inside of single quotes. Put both patterns into one set of double quotes.

Finally, you shouldn't put the command inside of brackets. Something like this should work:

Code:
if egrep -qw "$D|$L" testfile
then
    execute some command
fi

This User Gave Thanks to agama For This Post:
bludhemn
# 6  
Old 06-27-2011
Quote:
if grep -qw '"$D"|"$L"' testfile
It is hard to guess what you intended from faulty code. Please describe the condition in words.
Things to bear in mind.
Variables enclosed by single quote characters are not expanded.
The "grep" command does not recognise "|" as meaning "or". The "egrep" command does.
A command sequence in an "if" statement does not execute automatically. It needs either backticks or $( ) command syntax.
# 7  
Old 06-27-2011
Quote:
Originally Posted by methyl
A command sequence in an "if" statement does not execute automatically. It needs either backticks or $( ) command syntax.
Beg to differ, but at least in Kshell and bash a command executes without $(..) or `..` when placed on an if.

Code:
spot: ls >/tmp/x
spot: if grep -q foo /tmp/x
> then
> echo true
> fi
true

Last edited by agama; 06-27-2011 at 01:47 AM.. Reason: typo
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