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Top Forums Shell Programming and Scripting awk regexp to print repetitive pattern Post 302977316 by Don Cragun on Friday 15th of July 2016 05:54:48 PM
Old 07-15-2016
Quote:
Originally Posted by yifangt
Can I say there is no regexp for this case in awk, similar to your perl script ?perl -e '{print "-\t"x11, "-\n"}'
Thanks a lot!
No. You can say that a string argument in an awk print statement is a string; not a regular expression. If you want an ERE to select lines containing exactly 11 copies of "-\t" followed by a final "-" and only print those lines, you could try:
Code:
awk 'BEGIN{print "start"; OFS="-\t"; $12="-"; print; print "end"}'|awk '/^(-\t){11}-$/'

which uses a regex in the 2nd awk script to print just that matched line out of the three lines printed by the 1st awk script

Note that redirecting the input from /dev/null won't hurt anything, but it isn't needed in an awk script that only contains one or more BEGIN clauses.
This User Gave Thanks to Don Cragun For This Post:
 

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GREP(1) 						      General Commands Manual							   GREP(1)

NAME
grep - search a file for a pattern SYNOPSIS
grep [ option ... ] pattern [ file ... ] DESCRIPTION
Grep searches the input files (standard input default) for lines (with newlines excluded) that match the pattern, a regular expression as defined in regexp(6). 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. -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. 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 '...'. SOURCE
/sys/src/cmd/grep.c SEE ALSO
ed(1), awk(1), sed(1), sam(1), regexp(6) DIAGNOSTICS
Exit status is null if any lines are selected, or non-null when no lines are selected or an error occurs. GREP(1)
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