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sed back reference error

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# 1  
Old 02-26-2015
Hammer & Screwdriver sed back reference error
I am trying to change a single line of a special file whose comment character is ! to show a path to the file in the comment. such as:

Code:
!!HFSS and mcm path:     \Signal_Integrity\Package_SI\Section_Models\C4toTrace\28nm\D6HS\SLC_5-2-5\GZ41_ICZ\NSSS\

to a different path and replace the !!HFSS and mcm path: text.

here is my code:
Code:
path='!! HFSS and mcm path: '$(pwd)

for file in $(find . -name "*s[48]p*")
do
  old=$(grep '!! HFSS\|!!HFSS' $file)
  sed -i "s@$old@$path@" $file
done

I get the following error for some but not all files!
Code:
sed: -e expression #1, char 260: Invalid back reference

can someone please help explain why it works for some files but not others?
Thanks,
Mike
Last edited by Scrutinizer; 02-26-2015 at 11:34 AM.. Reason: code tags, please!
# 2  
Old 02-26-2015
My guess is that your strings contains backslashes followed by numbers, which gets interpreted as a back reference. Note that sed substitute functions does not use strings, but rather regular expressions.

A safer way would be to use fixed strings, for example

Code:
path='!! HFSS and mcm path: '$(pwd)
awk -v p="$path" '/!! *HFS/{$0=p}1' file

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