Need help deciphering this Post: 302416821

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Top Forums UNIX for Dummies Questions & Answers Need help deciphering this Post 302416821 by Straitsfan on Tuesday 27th of April 2010 09:58:05 PM

04-27-2010

Registered User

Need help deciphering this

I'm reading about command substitutions and came across this little function in my book:

function lsd
{
date=$1
ls -l |grep -i "^.\{42\}$date"|cut -c55-
}

it's a little example which is supposed to select files by modification date, given as an argument to the function.

I can't figure out what the ^, ., and \{42\} means. The book says that the function tells UNIX to match any line that contains 41 characters followed by the function argument, with the date starting in column 42, then only printing the filenames, which start in column 55, but like I said I don't know what these symbols mean (or how they 'translate'). The only thing I've found about the ^ so far is that it's a 'word designator' but I'm not sure if that applies here.

I'm also not sure how to translate the .\{42\} either.

By the way, how do I find out what the column layout for the ls -l command is? (if I've phrased that correctly), that is, what column each part of the listing begins at?

Straitsfan

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LEARN ABOUT OPENDARWIN

comm

COMM(1) 						    BSD General Commands Manual 						   COMM(1)

NAME

     comm -- select or reject lines common to two files

SYNOPSIS

     comm [-123i] file1 file2

DESCRIPTION

     The comm utility reads file1 and file2, which should be sorted lexically, and produces three text columns as output: lines only in file1;
     lines only in file2; and lines in both files.

     The filename ``-'' means the standard input.

     The following options are available:

     -1      Suppress printing of column 1.

     -2      Suppress printing of column 2.

     -3      Suppress printing of column 3.

     -i      Case insensitive comparison of lines.

     Each column will have a number of tab characters prepended to it equal to the number of lower numbered columns that are being printed.  For
     example, if column number two is being suppressed, lines printed in column number one will not have any tabs preceding them, and lines
     printed in column number three will have one.

     The comm utility assumes that the files are lexically sorted; all characters participate in line comparisons.

DIAGNOSTICS

     The comm utility exits 0 on success, and >0 if an error occurs.

SEE ALSO

     cmp(1), diff(1), sort(1), uniq(1)

STANDARDS

     The comm utility conforms to IEEE Std 1003.2-1992 (``POSIX.2'').

HISTORY

     A comm command appeared in Version 4 AT&T UNIX.

BSD
								   June 6, 1993 							       BSD