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Full Discussion: sed pattern matching question
Top Forums Shell Programming and Scripting sed pattern matching question Post 302518171 by mirni on Thursday 28th of April 2011 07:33:55 PM
Old 04-28-2011
Quote:
From what I can tell the whole string (ABCD|/p) is a literal.
Mmmmm... no.
The string 'ABCD|' is a literal, the rest '/p' is the end of regex ('/') and print command ('p'). So the first sed command
Code:
sed -n -e '/^.*ABCD|/p'

is an instruction to print only lines containing 'ABCD|'. There is some redundancy there; the following would do the same:
Code:
sed -n -e '/ABCD|/p'

The second sed removes the beginning of line until ABCD| including. Note that matching here is greedy, so if you have multiple instances of ABCD| there, the pattern is gonna match the longest possible substring. E.g.:
Code:
$ echo "blah|ABCD|hhhh|fals.;and&+324ABCD|ooo|ABCD" | sed -e 's/^.*ABCD|//' 
ooo|ABCD

The third one removes trailing '|ABCD'

We could simplify this as :
Code:
sed -n '/ABCD|/{  #do the following on lines containing "ABCD|"
            s/^.*ABCD|// ;  #eat the longest substring from beginning to "ABCD|"
            s/|ABCD$//;     # eat the  last "|ABCD" just before end of line
            p }'               # and print it

Last edited by mirni; 04-28-2011 at 08:40 PM..
This User Gave Thanks to mirni For This Post:
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LEARN ABOUT OSX

mbr_check_service_membership

MBR_CHECK_MEMBERSHIP(3) 				   BSD Library Functions Manual 				   MBR_CHECK_MEMBERSHIP(3)

NAME

     mbr_check_membership, mbr_check_service_membership -- check whether a user is a member of a group or service ACL

SYNOPSIS

     #include <membership.h>

     int
     mbr_check_membership(uuid_t user, uuid_t group, int *ismember);

     int
     mbr_check_service_membership(uuid_t user, const char *service, int *ismember);

DESCRIPTION

     mbr_check_membership() tests if a given user is a member of a group (either direct or indirect via a nested group).  ismember is set to 1 if
     the user is a member or 0 if not a member of the group.  mbr_check_service_membership() similarly tests if a given user is a member of a ser-
     vice ACL group.  Service ACLs are special groups defined with the prefix "com.apple.access_".  The service is then prefixed (e.g., "afp"
     would check "com.apple.access_afp").  There is a special group that grants accessto all services called "com.apple.access_all_services".

     Users may belong to any number of groups.	mbr_check_membership() should always be used to check group membership, rather than calling
     getgroups(2) or getgrouplist(2).  The setgroups(2) and getgroups(2) routines are limited to a fixed number of gids, and so may not include
     all of a user's groups.

     There are two special cases.  If the two uuids are equal, then ismember is set to 1.  If the group uuid is equal to the reserved "everyone"
     uuid (ABCDEFAB-CDEF-ABCD-EFAB-CDEF0000000C), then ismember will be set to 1 for any valid user.

     Group membership information is managed by opendirectoryd(8).

RETURN VALUES

     mbr_check_membership() does not test whether group exists or not.	Querying membership for a nonexistent group will result in ismember being
     set to 0.	The function returns 0 on success or one of the following error codes on failure:

     [EIO]		Communication with openditectoryd(8) failed.

     [ENOENT]		user can not be found.

     mbr_check_service_membership() is identical to mbr_check_membership() except that ENOENT means no service ACL has been defined.

SEE ALSO

     odutil(1), setgroups(2), getgroups(2), mbr_uid_to_uuid(3), opendirectoryd(8)

Mac OS X							 November 5, 2011							  Mac OS X
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