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Can't find the mistake in sed expression

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# 1  
Old 02-16-2009
Question Can't find the mistake in sed expression
Hi there,
Can anyone help me find the correct expression for sed.
I want to repace iface eth0 inet wathever
with iface eth0 inet static

Quote:
deneb:~# sed '/^iface eth0 inet (.*)/ s/\1/static/' /etc/network/interfaces
sed: -e expression #1, char 36: Invalid back reference
deneb:~# sed -r '/^iface eth0 inet (.*)/ s/\1/static/' /etc/network/interfaces
sed: -e expression #1, char 36: Invalid back reference
deneb:~# sed '/^iface eth0 inet \(.*\)/ s/\1/static/' /etc/network/interfaces
sed: -e expression #1, char 38: Invalid back reference
deneb:~# sed -r '/^iface eth0 inet \(.*\)/ s/\1/static/' /etc/network/interfaces
sed: -e expression #1, char 38: Invalid back reference
Thanks for your help
Santiago
# 2  
Old 02-16-2009
Try:

Code:
sed 's/\(iface eth0 inet\).*/\1 static/'

Regards
# 3  
Old 02-16-2009
Code:
sed '/^iface eth0 inet / s/^\(iface eth0 inet\).*/\1 static/' /etc/network/interfaces

A back reference is always only valid within the substitution and can't be kept across commands.
# 4  
Old 02-16-2009
Code:
sed '/iface eth0 inet/s/\(.*\) .*$/\1 static/' file

# 5  
Old 02-16-2009
Code:
$ echo 'iface eth0 inet wathever foo' | sed '/^iface eth0 inet / s/^\(iface eth0 inet\).*/\1 static/'
iface eth0 inet static

Code:
$ echo 'iface eth0 inet wathever foo' | sed '/^iface eth0 inet / s/^\(iface eth0 inet\) *\([^ ][^ ]*\) *\(.*\)/\1 static \3/'
iface eth0 inet static foo

# 6  
Old 02-16-2009
Thanks Franklin52, pludi, danmero and vgersh99.
pludi is right when he says:
Quote:
Originally Posted by pludi
[code]A back reference is always only valid within the substitution and can't be kept across commands.
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