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Why do we use a colon (:) in grep?

 
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# 1  
Old 01-24-2012
Why do we use a colon (:) in grep?
Can some one please explain why do we use colon in a grep statement .
for eg:
Code:
ORACLE_SID=$(grep :$(echo $JOBNAME |cut -c1-3): ${SWENV_TAB}|awk -F: '{print $1}')


Thanks in advance
Sri
Last edited by Franklin52; 01-24-2012 at 11:14 AM.. Reason: Please use code tags for code and data samples, thank you
# 2  
Old 01-24-2012
Seems that's what the script wants to find in ${SWENV_TAB}.. Possibly the output looks like

Code:
SID:PID:possibly more stuff

From which the awk statement will grab $1, which is the SID. In other words: it's a literal ':' to be found in the file.
# 3  
Old 01-24-2012
Because we're looking for the first field of a record that contains a value which consists of the first three characters of the variable JOBNAME bounded by colons in the file named in the SWENV_TAB variable.

Or to rephrase it there are 2 parameters to the grep statement the first can be written as ":$(echo $JOBNAME | cut -c1-3):" the $(...) construct causes the contents to be evaluated
# 4  
Old 01-24-2012
Why do we use a colon (:) in grep?
Thanks a ton neutronscott and Skrynesaver
Asking this out of curiosity ..

i) what will happen to the same grep statement if I remove the colon or


ii)what will happen if there is a different delimiter ,lets say (,) the will
Code:
ORACLE_SID=$(grep ,$(echo $JOBNAME |cut -c1-3),${SWENV_TAB}|awk -F: '{print $1}')

give me the same output..

Thanks
Sri
Moderator's Comments:
Mod Comment Please use next time code tags for your code and data
Last edited by vbe; 01-24-2012 at 05:27 AM..
# 5  
Old 01-24-2012
so long as the delimiter has no meaning to the shell, then yes any delimiter can be used, as "," has no special meaning to the shell in this context, it should work.
# 6  
Old 01-24-2012
IOW, , or : has no special meaning to grep. They added : to the pattern because they were actually looking for it.
 
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