10-16-2009
Hi,
$$ stands for process id of the running process. To include this in a filename is a way of making the file or directory unique.
The second expression is missing a closing parenthesis. But it set k to the number of lines that do not contain the characters " ", "+", "-","0", "1" or formfeed. Whether the formfeed detection will work depends on your version of grep. If it doesn't then this code will also exclude lines that contain the character "f" from the count and that probably is not what was intended.
The third expression means if the 24 characters starting at position 2 in the variable "file" contain 13 or more digits then print the character "N" concatenated by the content of the variable "file" .
Last edited by Scrutinizer; 10-16-2009 at 06:05 AM..
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LEARN ABOUT DEBIAN
plan9-grep
GREP(1) General Commands Manual GREP(1)
NAME
grep, g - search a file for a pattern
SYNOPSIS
grep [ option ... ] pattern [ file ... ]
g [ option ... ] pattern [ file ... ]
DESCRIPTION
Grep searches the input files (standard input default) for lines that match the pattern, a regular expression as defined in regexp(7) with
the addition of a newline character as an alternative (substitute for |) with lowest precedence. Normally, each line matching the pattern
is `selected', and each selected line is copied to the standard output. The options are
-c Print only a count of matching lines.
-h Do not print file name tags (headers) with output lines.
-e The following argument is taken as a pattern. This option makes it easy to specify patterns that might confuse argument parsing,
such as -n.
-i Ignore alphabetic case distinctions. The implementation folds into lower case all letters in the pattern and input before interpre-
tation. Matched lines are printed in their original form.
-l (ell) Print the names of files with selected lines; don't print the lines.
-L Print the names of files with no selected lines; the converse of -l.
-n Mark each printed line with its line number counted in its file.
-s Produce no output, but return status.
-v Reverse: print lines that do not match the pattern.
-f The pattern argument is the name of a file containing regular expressions one per line.
-b Don't buffer the output: write each output line as soon as it is discovered.
Output lines are tagged by file name when there is more than one input file. (To force this tagging, include /dev/null as a file name
argument.)
Care should be taken when using the shell metacharacters $*[^|()= and newline in pattern; it is safest to enclose the entire expression in
single quotes '...'. An expression starting with '*' will treat the rest of the expression as literal characters.
G invokes grep with -n and forces tagging of output lines by file name. If no files are listed, it searches all files matching
*.C *.b *.c *.h *.m *.cc *.java *.cgi *.pl *.py *.tex *.ms
SOURCE
/src/cmd/grep
/bin/g
SEE ALSO
ed(1), awk(1), sed(1), sam(1), regexp(7)
DIAGNOSTICS
Exit status is null if any lines are selected, or non-null when no lines are selected or an error occurs.
GREP(1)