Usage of grep '^$1' filename


 
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# 1  
Old 08-20-2015
Usage of grep '^$1' filename

There is a file name list_filenames.dat, this has all the list of all files I need to encrypt, I did not understand what the following syntax is doing:

Code:
grep -s "^$1" list_filenames.dat

, when I manually run this command it just returns all the lines, what is the usage of this ? can someone explain?

Last edited by Don Cragun; 08-20-2015 at 03:55 AM.. Reason: Add CODE and ICODE tags.
# 2  
Old 08-20-2015
That grep command copies all lines from the named file that contain the string specified as the 1st argument to your script at the start of those lines. (If you invoke the script with no arguments, it will match and print every line in the file.)

Why you would want to use that command in a script that is supposed to encrypt all of the files listed in that file is not clear to me.
# 3  
Old 08-20-2015
Thank you very much, I agre I dont have to go with syntax, however I got confused understandin $1, how is it exactly behaving and this clears my understanding.
# 4  
Old 08-20-2015
$1 in shell is the first positional parameter, either supplied when calling the script or function, or (in bash) set by set -- text1 text2 . . ..
# 5  
Old 08-20-2015
Quote:
Originally Posted by RudiC
$1 in shell is the first positional parameter, either supplied when calling the script or function, or (in bash) set by set -- text1 text2 . . ..
Code:
set -- arg...

isn't just available in bash; it is required in all POSIX-conforming shells.

Note that the -- is only required if the 1st arg starts with a - or + character or if you want to use the command:
Code:
set --

to unset all positional parameters.
 
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