Delete lines in a file containing argument passed on command line - database

Question

I'm trying to delete specific lines based on the argument passed in.
My data.txt file contains
Cpu 500 64 6
Monitor 22 42 50
Game 32 64 128
My del.sh contains
myvar=$1
sed'/$myvar/d' data.txt > temp.txt
mv temp.txt > data.txt
but it just prints every line in temp.txt to data.txt....however
sed '/64/d' data.txt > temp.txt
will do the correct data transfer (but I don't want to hardcode 64), I feel like there's some kind of syntax error with the argument. Any input please

Answer 1

It's because of the single quotes, change them to double quotes. Variables inside single quotes are not interpolated, so you are sending the literal string $myvar to sed, instead of the value of $myvar.
Change:
sed '/$myvar/d' data.txt
to:
sed "/$myvar/d" data.txt
Note: You will run into issues when $myvar contains regular expression meta characters or forward slashes as pointed out in this response from Ed Morton. If you are not in complete control of your input you will need to find another avenue to accomplish this.

Answer 2

Assuming this is undesirable behavior:
$ cat file
Cpu 500 64 6
Monitor 22 42 50
Game 32 64 128
$ myvar=6
$ sed "/$myvar/d" file
Monitor 22 42 50
$ myvar=/
$ sed "/$myvar/d" file
sed: -e expression #1, char 3: unknown command: `/'
$ myvar=.
$ sed "/$myvar/d" file
$
Try this instead:
$ myvar=6
$ awk -v myvar="$myvar" '{for (i=1; i<=NF;i++) if ($i == myvar) next }1' file
Monitor 22 42 50
Game 32 64 128
$ myvar=/
$ awk -v myvar="$myvar" '{for (i=1; i<=NF;i++) if ($i == myvar) next }1' file
Cpu 500 64 6
Monitor 22 42 50
Game 32 64 128
$ myvar=.
$ awk -v myvar="$myvar" '{for (i=1; i<=NF;i++) if ($i == myvar) next }1' file
Cpu 500 64 6
Monitor 22 42 50
Game 32 64 128
and if you think you can just escape the /s and use sed, you can't because you might be adding a 2nd backslash to one already present:
$ foo='\/'
$ myvar=${foo//\//\\\/}
$ sed "/$myvar/d" file
sed: -e expression #1, char 5: unknown command: `/'
$ awk -v myvar="$myvar" '{for (i=1; i<=NF;i++) if ($i == myvar) next }1' file
Cpu 500 64 6
Monitor 22 42 50
Game 32 64 128
This is simply NOT a job you can in general do with sed due to it's syntax and it's restriction of only allowing REs in it's search.

Answer 3

You can also use awk to do the same,
awk '!/'$myvar'/' data.txt > temp.txt && mv temp.txt data.txt
Use -i option in addition to what #SeanBright proposed. Then you won't need > temp.txt and mv temp.txt data.txt.
sed -i "/$myvar/d" data.txt