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Using variable in sed

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# 1  
Old 02-20-2013
Using variable in sed
Hi all,

Somescript.sh looks like this:
Code:
#!/bin/sh
#  somecript.sh

somecommand1

somecommand2

#End

exit

Now I want to add somecommand3 to somescript.sh above #End

I now how to do this:
Code:
sed -ie '/#End/i\
somecommand3\
' /location/of/somescript.sh

This works fine. But now I want to add a variable the same way. I can't get this to work. I thought something like this:
Code:
command=somecommand3

sed -ie '/#End/i\
"$command"\
' /location/of/somescript.sh

But this just adds "$command".

Thanks
# 2  
Old 02-20-2013
The shell sees a multi-line 'string' where $command is not seen and substituted.
Code:
sed -ie '/#End/i\
"$command"\
' /location/of/somescript.sh

The trick is to have 'string1' $command 'string2', so the $command is seen and substituted by the shell.
Code:
sed -ie '/#End/i\
'$command'\
' /location/of/somescript.sh

or
Code:
sed -ie '/#End/i\
'"$command"'\
' /location/of/somescript.sh

The latter uses the fact that the shell sees and substitutes $command within a "string".
# 3  
Old 02-20-2013
Quote:
Originally Posted by MadeInGermany
Code:
sed -ie '/#End/i\
'$command'\
' /location/of/somescript.sh

Not recommended. If command contains a multi-word string, the sed command line will break.
# 4  
Old 02-21-2013
Quote:
Originally Posted by mattiasvdm
I thought something like this:
Code:
command=somecommand3

sed -ie '/#End/i\
"$command"\
' /location/of/somescript.sh

But this just adds "$command".
The reason is that inside a single-quoted string double-quoting has no effect. From the POV of the shell, though, you are inside a single-quoted string. This should work:

Code:
sed -ie '/#End/i\
'"$command"'\
' /location/of/somescript.sh

Note that the single-quoted string ends, then a double-quoted string starts and when this ends another single-quoted string starts. This may look cumbersome, but it is the only way to ensure the sed-command will not break if "$command" contains whitespace.

I hope this helps.

bakunin
# 5  
Old 02-21-2013
Thanks guys,

I get the point. Smilie

Next challenge:

The variable is a multi-line variable:
Code:
read -d '' command <<EOF
command3a
command3b
command3c
EOF

Now if I run:
Code:
sed -ie '/#End/i\
'"$command"'\
' /location/of/somescript.sh

I get:
Code:
sed: 3: "/#End/i\
command3a
command3b ...": invalid command code c

# 6  
Old 02-21-2013
What shell do you use?
Try:
Code:
sed -ie '/#End/i\
'"${command//$'\n'/\\$'\n'}"'\
' /location/of/somescript.sh

# 7  
Old 02-21-2013
bash

And it works! Can you please explain how it works because you lost me at the \\//\\ signs... Smilie
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