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replace character only in first line of a file

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# 1  
Old 12-21-2009
replace character only in first line of a file
Hi,

I need to replace a character in a specific position in only the first line of a
file (actually many files). Change T to a P in position 103.

I'm on solaris and my implementation of sed doesn't have the -r capability.

Thx,

Tim
# 2  
Old 12-21-2009
one way:
Code:
# assumes pos 103 is always a T -> P change
for fname in $( find . -name 'filetofix*')
do
     awk '{if(FNR==1) 
               {printf("%s%s%s", substr($0,1,102), "P", substr($0,104) )} 
             else 
               {print} ' $fname > ${fname}.fixed
done

# 3  
Old 12-21-2009
Code:
$ cat > t
testing...
test of second line.
$ sed -e '1s/\(.\{4\}\).\(.*\)/\1P\2/' t
testPng...
test of second line.

If you wanted the 103rd character to be replaced, then use 102 instead of 4 in the sed command.
Code:
sed -e '1s/\(.\{102\}\).\(.*\)/\1P\2/' t

And if you have the -i option, then you can use it which will edit the file itself.
Code:
sed -ie '1s/\(.\{102\}\).\(.*\)/\1P\2/' t

# 4  
Old 12-21-2009
Thanks! I couldn't get the awk to work, but the sed command did the trick.

Tim
# 5  
Old 12-21-2009
Try this awk:

Code:
awk 'BEGIN{FS=OFS=""} {if (NR==1&&$103="T") $103="P" }1' input.txt

# 6  
Old 12-21-2009
If you have the -r option:
Code:
sed -r '1s/^(.{102})T/\1P/' infile

otherwise
Code:
sed '1s/^\(.\{102\}\)T/\1P/' infile

The ^ caret is important otherwise you may end up matching some T in a different column > 102
Last edited by Scrutinizer; 12-21-2009 at 05:26 PM..
# 7  
Old 12-22-2009
this will work
Code:
awk 'BEGIN{FS=OFS=""} {if (NR==1&&$103="T") $103="P" }1' file.txt

Last edited by radoulov; 12-22-2009 at 04:07 AM.. Reason: Please use code tags.
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