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Full Discussion: Understanding sed
Top Forums Shell Programming and Scripting Understanding sed Post 302774009 by Scrutinizer on Friday 1st of March 2013 04:06:20 AM
Old 03-01-2013
Hi, the first one deletes the second field only if it consists of one character... It replace the first field and a colon + a character and a colon with the first field (that was captured with \( .. \) and recalled by\1) and two colons

The second replaces any number of non-colons and a colon by a colon, the number two means the it does this with the second occurrence on a line...
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dialups(4)						     Kernel Interfaces Manual							dialups(4)

NAME
dialups, d_passwd - dialup security control DESCRIPTION
and are used to control the dialup security feature of (see login(1)). If is present, the first word on each line is compared with the name of the line upon which the login is being performed (including the as returned by (see ttyname(3C)). If the login is occurring on a line found in dialup security is invoked. Anything after a space or tab is ignored. When dialup security is invoked, requests an additional password, and checks it against that found in The command name found in the ``pro- gram to use as shell'' field of is used to select the password to be used. Each entry in consists of three fields, separated by colons. The first is the command name, matching an entry in The second is the encrypted password to be used for dialup security for those users logging in to use that program. The third is commentary, but the second colon is required to delimit the end of the password. A null password is designated with two adjacent colons. The entry for is used if no other entry matches the command name taken from FILES
dial-in tty lines passwords SEE ALSO
login(1), passwd(4). dialups(4)
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