Use sed instead of lua

[pickfire]

Hi, I doesn't know what does these lua means but I think I can replace it with something else which is shorter and reduce the dependencies.

set_config_var() {
  lua - "$1" "$2" "$3" <<EOF > "$3.bak"
local key=assert(arg[1])
local value=assert(arg[2])
local fn=assert(arg[3])
local file=assert(io.open(fn))
local made_change=false
for line in file:lines() do
  if line:match("^#?%s*"..key.."=.*$") then
    line=key.."="..value
    made_change=true
  end
  print(line)
end
if not made_change then
  print(key.."="..value)
end
EOF
mv "$3.bak" "$3"
}

I think that function is to change arm_freq=700 to arm_freq=900. You can use sed in that way too:

function set_config_var() {
  grep -q "^$1=" $3 && sed -i "/^$1=/c $1=$2" $3 || echo "$1=$2" >> $3
  return 0  # search $1 and change "$1=*" to "$1=$2" or append "$1=$2" to EOF
}

And for the function to get the config values you can do it with sed too:

get_config_var() {
  lua - "$1" "$2" <<EOF
local key=assert(arg[1])
local fn=assert(arg[2])
local file=assert(io.open(fn))
for line in file:lines() do
  local val = line:match("^#?%s*"..key.."=(.*)$")
  if (val ~= nil) then
    print(val)
    break
  end
end
EOF
}

With sed:

get_config_var() {
  sed -n "s/$1=// p" $2
}

Sorry that I didn't send you a pull request as I don't think I should fork it just for these code. I hope you can reduce the dependencies and shorten the code by using a shorter function. Thanks.
Ivan Tham [email protected]

[alecthegeek]

The justification is that Lua is always present on Debian and is easier to read (although I use sed in all my scripts, but I'm old skool)

[mobluse]

I'm not sure the SEd-functions does the same as the Lua-functions. I don't know Lua. I think the Lua-functions are better now because they seem to uncomment a commented key-value pair. With these suggested functions with SEd the commented key-value pairs would remain commented and the key-value pairs are inserted at the end of the file. This leads to a more difficult-to-read configuration file, where the documentation in comments is in one place and the key-value pair in another. One could replace the Lua-functions with more complex Sed- or AWK-functions. I think this should be done because one should not require that Lua is installed. Also, Lua is not that easy to understand, e.g. what does "^#?%s*" mean?

BTW I found this useful discussion: http://stackoverflow.com/questions/2464760/modify-config-file-using-bash-script

[alecthegeek]

1. Lua is always present in Raspian
2. sed and Lua regex are equally opaque. #? means optionally one comment char. It would be same in sed

Having said all that I use the following style in my Pi scripts

setConfigOption() {
  CONFIG_FILE=/boot/config.txt
  if grep "$1=" $CONFIG_FILE ; then
    sudo sed --in-place -re "s/^#?$1=.+$/$1=$2 #$UPDATE_LABEL/" $CONFIG_FILE
  else
    echo $1=$2'  #'$UPDATE_LABEL| sudo tee -a $CONFIG_FILE
  fi
}

[pickfire]

^# $1 could also mean one commented char. To uncomment, use:

sed -i "s/^# $1/$1/" $CONFIG_FILE

^ means the first character in the line and # is the first character, $ is the last character in the line.

I prefer to have a short one:

function set_config_var() {
  grep -q "^$1=" $3 && sed -i "/^$1=/c $1=$2" $3 || echo "$1=$2" >> $3
  return 0  # search $1 and change "$1=*" to "$1=$2" or append "$1=$2" to EOF
}

set_config_var('cpu_freq', 1000, /boot/config.txt)