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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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XmTextFindString(3X)													      XmTextFindString(3X)

NAME
XmTextFindString - A Text function that finds the beginning position of a text string SYNOPSIS
#include <Xm/Xm.h> Boolean XmTextFindString (widget, start, string, direction, position) Widget widget; XmTextPosition start; char *string; XmTextDirection direction; XmTextPosition *position; DESCRIPTION
XmTextFindString locates the beginning position of a specified text string. This routine searches forward or backward for the first occur- rence of the string starting from the given start position. If it finds a match, the function returns the position of the first character of the string in position. Specifies the Text widget ID. Specifies the character position from which the search proceeds. This is an integer number of characters from the beginning of the text buffer. The first character position is 0. Specifies the search string. Indicates the search direction. It is relative to the primary direction of the text. The possible values are: The search proceeds toward the end of the text buffer. The search proceeds toward the beginning of the text buffer. Specifies the pointer in which the first charac- ter position of the string match is returned. This is an integer number of characters from the beginning of the buffer. The first charac- ter position is 0. If the function returns False, this value is undefined. For a complete definition of Text and its associated resources, see XmText(3X). RETURN VALUE
Returns True if a string match is found; otherwise, returns False. SEE ALSO
XmText(3X), XmTextFindStringWcs(3X) XmTextFindString(3X)
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