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Full Discussion: substitute a string on a specific position for specific lines
Top Forums Shell Programming and Scripting substitute a string on a specific position for specific lines Post 302480599 by ctsgnb on Wednesday 15th of December 2010 10:22:45 AM
Old 12-15-2010
@anurag

Ooops, you are true, i totally forgot that position case ... here is an even better
- need caret ^ to be exact regarding the position otherwise the \(.....<n_times>\)TOCHANGE could also be match at a position greater than the expected one
- use the $! tip to avoid last line)
- therefore avoid the use of additionnal file opening & line counting of the wc -l
- no need of sed -e option

Code:
sed '3s/^\(...........\)TOCHANGE\(.*\)/\1ABCABCAB\2/;$!{4,$s/^\(........\)TOCHANGE\(.*\)/\1ABCABCAB\2/}' infile

Code:
# cat tst1
12345678901TOCHANGE12345
12345678901TOCHANGE12345
12345678901TOCHANGE12345
12345678901TOCHANGE12345
12345678901TOCHANGE12345
12345678901TOCHANGE12345
12345678901TOCHANGE12345
# cat tst2
12345678TOCHANGE12345
12345678TOCHANGE12345
12345678TOCHANGE12345
12345678TOCHANGE12345
12345678TOCHANGE12345
12345678TOCHANGE12345
12345678TOCHANGE12345
# sed '3s/^\(...........\)TOCHANGE\(.*\)/\1ABCABCAB\2/;$!{4,$s/^\(........\)TOCHANGE\(.*\)/\1ABCABCAB\2/}' tst1
12345678901TOCHANGE12345
12345678901TOCHANGE12345
12345678901ABCABCAB12345
12345678901TOCHANGE12345
12345678901TOCHANGE12345
12345678901TOCHANGE12345
12345678901TOCHANGE12345
# sed '3s/^\(...........\)TOCHANGE\(.*\)/\1ABCABCAB\2/;$!{4,$s/^\(........\)TOCHANGE\(.*\)/\1ABCABCAB\2/}' tst2
12345678TOCHANGE12345
12345678TOCHANGE12345
12345678TOCHANGE12345
12345678ABCABCAB12345
12345678ABCABCAB12345
12345678ABCABCAB12345
12345678TOCHANGE12345

Last edited by ctsgnb; 12-15-2010 at 11:52 AM.. Reason: forgot the caret ^
 

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LEARN ABOUT PHP

mb_strpos

MB_STRPOS(3)								 1							      MB_STRPOS(3)

mb_strpos - Find position of first occurrence of string in a string

SYNOPSIS

       int mb_strpos (string  $haystack, string  $needle, [int	$offset], [string  $encoding = mb_internal_encoding()])

DESCRIPTION

	Finds position of the first occurrence of a string in a string.

	Performs  a  multi-byte  safe strpos(3) operation based on number of characters. The first character's position is 0, the second character
       position is 1, and so on.

PARAMETERS

	      o $haystack
		- The string being checked.

	      o $needle
		- The string to find in $haystack. In contrast with strpos(3), numeric values are not applied as the ordinal value of a character.

	      o $offset
		- The search offset. If it is not specified, 0 is used.

	      o $encoding
		-The $encoding parameter is the character encoding. If it is omitted, the internal character encoding value will be used.

RETURN VALUES

	Returns the numeric position of the first occurrence of $needle in the $haystack string. If $needle is not found, it returns FALSE.

SEE ALSO

       mb_internal_encoding(3), strpos(3).

PHP Documentation Group 													      MB_STRPOS(3)
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