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Full Discussion: sed command to Insert a line before the last four lines of the file
Top Forums UNIX for Dummies Questions & Answers sed command to Insert a line before the last four lines of the file Post 302955567 by Don Cragun on Friday 18th of September 2015 04:35:23 PM
Old 09-18-2015
If you're trying to learn how to use sed, you should also learn to recognize things that sed was not designed to do (like counting lines backwards from the end of a file). A tool like ed or ex could handle an assignment like this without needing to invoke tac twice to get data in a format that sed can handle... For instance, if you want to update the contents of the file:
Code:
#!/bin/ksh
LN=4
IP=$((LN - 1))
ed -s file.txt <<-EOF
        .-${IP}i
	.
	w
	q
EOF

or if you just want to print the updated contents (so you can redirect the output to a different file or just view the update):
Code:
#!/bin/ksh
LN=4
IP=$((LN - 1))
ed -s file.txt <<-EOF
        .-${IP}i
NEW LINE!
        .
        1,$ p
        Q
EOF

This User Gave Thanks to Don Cragun For This Post:
disedorgue
 

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LEARN ABOUT HPUX

fmt

fmt(1)							      General Commands Manual							    fmt(1)

NAME

       fmt - format text

SYNOPSIS

       width] [file...]

DESCRIPTION

       The  command is a simple text formatter that fills and joins lines to produce output lines of (up to) the number of characters specified in
       the width option.  The default width is 72.  concatenates the arguments.  If none are given, formats text from the standard input.

       Blank lines are preserved in the output, as is the spacing between words.  does not fill lines beginning with a	period	for  compatibility
       with Nor does it fill lines starting with

       Indentation is preserved in the output and input lines with differing indentation are not joined (unless is used).

       can also be used as an in-line text filter for the command:

       reformats the text between the cursor location and the end of the paragraph.

   Options
       recognizes the following options:

	      Crown margin mode.
		    Preserve the indentation of the first two lines within a paragraph and align the left margin of each subsequent line with that
		    of the second line.  This is useful for tagged paragraphs.

	      Split lines only.
		    Do not join short lines to form longer ones.  This prevents sample lines of code, and other such "formatted" text, from  being
		    unduly combined.

	      Fill output lines to up to
		    width columns.

WARNINGS

       The width option is acceptable for BSD compatibility, but it may go away in future releases.

SEE ALSO

       nroff(1), vi(1).

																	    fmt(1)
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