Searching for a specific string in a file

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# 8  
Old 06-27-2011
Originally Posted by methyl
It is hard to guess what you intended from faulty code. Please describe the condition in words.
Oh sorry, I thought it was clear from my 1st post that I was trying to search for multiple strings (of which one was defined ..$D)!!

Originally Posted by agama
Second, your variables won't expand inside of single quotes. Put both patterns into one set of double quotes.
Dint know this one, Thank you!

Originally Posted by agama
Finally, you shouldn't put the command inside of brackets.
Can you explain why this is so?
# 9  
Old 06-27-2011
Can you explain why this is so?
"if" waits a command, and "[" is just a command. Really this is a synonym for "test". When command executes it returns exit code. If exit code == 0 then "if" counts it as true condition and executes commands in its body.

When you write, for example
if [ -f 'some_file' ]; then ...

really you run the command:
if test -f 'some_file' ; then ...

In case of grep - this command returns 0 if it finds matches or non-0 if it's not. This is perfect condition for "if".

Excuse me if something is unclear. I'm working on my English.
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