Using sed to replace single line in while read loop - bash

Question

I'm needing help setting up a bash script for initializing some BC's in a file. Ideally, my program would iterate through each line and:
1) Read in BC type - (wall, outlet, inlet).
2) Change "type" field based on appropriate BC type.
Unfortunately, my program seems to replace all type fields in Step 2 instead of only the type field associated with the correct BC.
I think this has something to do with the sed command operating over the whole file instead of just the $line variable.
while IFS= read -r line || [[ -n "$line" ]]; do #go through each line of T2 file
if [[ $line == *wall_* ]] #if wall_*
then
echo "attempted to assign wall_*"
var=1 #wall #Go down 2 lines
elif [[ $line == *velocity-inlet* ]]
then
echo "attempted to assign outflow"
var=2 #inlet
elif [[ $line == *outflow* ]]
then
var=3 #outlet
fi
echo $var
if [[ $line == *type* && $var == 1 ]]
then
sed -i 's/.*type.*/type zeroGradient/' 0/T3
echo "Attempted wall zeroGradient"
elif [[ $line == *type* && $var == 2 ]]
then
sed -i 's/.*type.*/type fixedValue\nvalue uniform (3 0 0)/' 0/T3
elif [[ $line == type* && $var == 3 ]]
then
sed -i 's/.*type.*/type zeroGradient/' 0/T3
fi
sed -i '/nFaces*/d' 0/T3 #Deletes irrelevant stuff from boundary file copy
sed -i '/startFace*/d' 0/T3
done <0/T3.
For example, it is supposed to change:
velocity-inlet_1
{
type patch;
nFaces 336;
startFace 75515;
}
outflow_2
{
type patch;
nFaces 136;
startFace 75851;
}
To:
velocity-inlet_1
{
type fixedValue;
value uniform (3 0 0);
}
outflow_2
{
type zeroGradient;
}
But instead changes it wrongly changes it to:
velocity-inlet_1
{
type fixedValue;
value uniform (3 0 0);
}
outflow_2
{
type fixedValue;
value uniform (3 0 0);
}
Help me stack overflow, you're my only hope.

Answer 1

You have a few issues. sed will effect a whole line by default, and you're not telling it which line to modify in the first place. You're also modifying a file as you read it. I might go with something like this:
var="none"
while IFS= read -r line; do
if [[ "$line" =~ "wall" ]]; then
var=wall
elif [[ "$line" =~ "velocity-inlet" ]]; then
var=inlet
fi
if [[ "$line" =~ "type" && "$var" == "wall" ]]; then
echo "$line" | sed 's|\(type *\).*|\1zeroGradient|'
elif [[ "$line" =~ "type" && "$var" == "inlet" ]]; then
echo "$line" | sed 's|\(type *\).*|\1uniform (3 0 0)|'
else
echo "$line"
fi
done
And then do
script.sh < 0/T3 > 0/T3.mod
You can of course modify this to read/write from particular files as well, and you can avoid sed (see here...)