Unix Tip: I SED BLANK

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UNIX HOT TIP

Unix Tip 3248 - December 27, 2008

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I SED BLANK

Using sed, you can remove blank lines, and lines that contain only whitespace, from a file using the following:

sed -e '/^[ ]*$/d' InputFile >OutputFile

Within the single quotes ('), the forward slashes (/) delimit the regular expression that will be interpreted by sed. The "d" before the closing single quote, tells sed to delete any lines that match the regular expression.

Within the regular expression, the caret (^) matches the beginning of a line. The []* matches zero to many occurrences of the character list between the open bracket
([) and the close bracket (]) (in the above regular expression, you must insert a space and a tab between the brackets). The dollar sign ($) matches the end of a line.

These three constructs together match any blank line or any line that contains only spaces and tabs (in any combination).

Since the standard operation of sed is to echo lines to stdout, all lines except blank lines (or lines that only contain whitespace) will be sent to OutputFile.

This tip generously supported by: tim.couger@wcom.com

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