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Top Forums Shell Programming and Scripting How to store regular expression in a variable? Post 302952201 by Don Cragun on Friday 14th of August 2015 05:04:49 PM
Old 08-14-2015
Note that you don't grep a folder (usually called a directory in UNIX and Linux environments). The grep utility searches for text in the contents of text files (not directories on most systems).

If you're trying to count the number of files in a directory that have names matching the globbing pattern stored in your shell variable named (confusingly) file_name, you could try something like:
Code:
ls $file_name | wc -l

which should work as long as there aren't any newline characters in your file names. If you have users who create filenames containing newline characters, or if you just want to use shell built-ins, a fast way to get what you want is:
Code:
set -- $file_name
echo $#

(assuming that you aren't using command line arguments or have already gathered what you need from them, and assuming that at least one file matching your pattern exists) or, if there might not be any matching files (but there also might be a file with a name that is your pattern):
Code:
set -- $file_name
if [ "$file_name" = "$1" ] && [ ! -e "$1" ]
then	echo 0
else	echo $#
fi

 

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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)
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