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sed, a stream editor

4.1 Centering Lines

This script centers all lines of a file on a 80 columns width. To change that width, the number in \{...\} must be replaced, and the number of added spaces also must be changed.

Note how the buffer commands are used to separate parts in the regular expressions to be matched--this is a common technique.

#!/usr/bin/sed -f # Put 80 spaces in the buffer 1 { x s/^$/ / s/^.*$/&&&&&&&&/ x } # del leading and trailing spaces y/tab/ / s/^ *// s/ *$// # add a new-line and 80 spaces to end of line G # keep first 81 chars (80 + a new-line) s/^\(.\{81\}\).*$/\1/ # \2 matches half of the spaces, which are moved to the beginning s/^\(.*\)\n\(.*\)\2/\2\1/