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Full Discussion: tail, grep and cut
Top Forums Shell Programming and Scripting tail, grep and cut Post 302172294 by sylaan on Monday 3rd of March 2008 09:52:03 AM
Old 03-03-2008
It was just an example to illustrate a real-world problem that I have.

Basically I need to tail a syslog file, grep for a certain pattern then display a certain field from the matched line. What I wanted to say with my example is that the "cut" after the "grep" is not producing anything, even though it should (as far as I can tell). It does not matter if I tail a syslog file or a testfile created by me, it should still work.

And sure, tail -f waits for more input but that does not matter, by default it should still list the last 10 lines or so from the file, which is plenty of input for my grep and cut.

--
Sylaan
 

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cut(1)							      General Commands Manual							    cut(1)

Name
       cut - cut out selected fields of each line of a file

Syntax
       cut -clist [file1 file2...]
       cut -flist [-dchar] [-s] [file1 file2...]

Description
       Use  the  command to cut out columns from a table or fields from each line of a file.  The fields as specified by list can be fixed length,
       that is, character positions as on a punched card (-c option), or the length can vary from line to line and be marked with a  field  delim-
       iter character like tab (-f option).  The command can be used as a filter.  If no files are given, the standard input is used.

       Use to make horizontal ``cuts'' (by context) through a file, or to put files together in columns.  To reorder columns in a table, use and

Options
       list	   Specifies  ranges  that must be a comma-separated list of integer field numbers in increasing order.  With optional - indicates
		   ranges as in the -o option of nroff/troff for page ranges; for example, 1,4,7; 1-3,8; -5,10 (short for 1-5,10);  or	3-  (short
		   for third through last field).

       -clist	   Specifies character positions to be cut out.  For example, -c1-72 would pass the first 72 characters of each line.

       -flist	   Specifies  the  fields  to be cut out.  For example, -f1,7 copies the first and seventh field only.	Lines with no field delim-
		   iters are passed through intact (useful for table subheadings), unless -s is specified.

       -dchar	   Uses the specified character as the field delimiter.  Default is tab.  Space or other characters with special  meaning  to  the
		   shell must be quoted.  The -d option is used only in combination with the -f option, according to XPG3 and SVID2/SVID3.

       -s	   Suppresses  lines  with  no	delimiter  characters.	 Unless  specified, lines with no delimiters are passed through untouched.
		   Either the -c or -f option must be specified.

Examples
       Mapping of user IDs to names:
       cut -d: -f1,5 /etc/passwd
       To set name to the current login name for the csh shell:
       set name=`who am i | cut -f1 -d" "`
       To set name to the current login name for the sh, sh5, and ksh shells:
       name=`who am i | cut -f1 -d" "`

Diagnostics
       "line too long"	   A line can have no more than 511 characters or fields.

       "bad list for c/f option"
			   Missing -c or -f option or incorrectly specified list.  No error occurs if a line has fewer fields than the list  calls
			   for.

       "no fields"	   The list is empty.

See Also
       grep(1), paste(1)

																	    cut(1)
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