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UNIX in a Nutshell: System V Edition

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The Sed Editor
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t

[address1][,address2]t [label]

Test if any substitutions have been made on addressed lines, and if so, branch to line marked by :label. (See b and :.) If label is not specified, control falls through to bottom of script. The t command is like a case statement in the C programming language or the shell programming languages. You test each case: when it's true, you exit the construct.

Example

Suppose you want to fill empty fields of a database. You have this:

ID: 1   Name: greg   Rate: 45
ID: 2   Name: dale
ID: 3

You want this:

ID: 1   Name: greg   Rate: 45   Phone: ??
ID: 2   Name: dale   Rate: ??   Phone: ??
ID: 3   Name: ????   Rate: ??   Phone: ??

You need to test the number of fields already there. Here's the script (fields are tab-separated):

/ID/{
s/ID: .* Name: .* Rate: .*/&   Phone: ??/p
t
s/ID: .* Name: .*/&   Rate: ??   Phone: ??/p
t
s/ID: .*/&   Name: ??     Rate: ??   Phone: ??/p
}


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