Let us be perfectly clear here. The requirements stated in post #1 in this thread and in post #5 in this thread are completely different. Adding a line containing === when $xyz expands to the string ON is in no way related to moving a line that contains only the string PIN 2 lines later in a file when $xyz expands to the string 2.

To move the first line in a file containing only the string PIN forward $xyz lines (if $xyz expands to a positive decimal value (with or without a leading +) or backwards $xyz lines (if $xyz expands to a negative decimal value), you could also try:

Code:

#!/bin/ksh
xyz=${1:-2}	# set default value for $xyz to 2, but use $1 if present.
if [ "${xyz#[+-]}" != "$xyz" ]
then	# $xyz is a signed value, clear $op
	op=
	# If $xyz is negative, decrement it by one to get the desired offset.
	[ "$xyz" -lt 0 ] && xyz=$((xyz - 1))
else	# $xyz is an unsigned value, set $op to a plus sign.
	op="+"
fi

# Use ed to move the first line that exactly matches the string "PIN" to the
# desired spot.
ed -s input.txt <<EOF
	H
	/^PIN$/;.m$op$xyz
	w
	q
EOF

This was written and tested using a Korn shell, but will work with any shell that uses Bourne shell syntax and performs the parameter and arithmetic expansions required by the POSIX standards.

If this script is invoked with no operands, with the operand 2, or the operand +2 it will move the 1st line in the file named input.txt that is exactly the string PIN two lines closer to the end of the file. If invoked with the operand -1, it will move that line one line closer to the start of the file. This will work with any non-zero decimal value as long as the that value is a valid for that line in the given file.

Note that the behavior of this script is slightly different from the script provided by RavinderSingh13:Both of our scripts meet your requirements as specified in post #5 in this thread. But, you left a lot of behavior unspecified that our scripts handle in different ways (as noted above).