I am using this command with variables
sed '/${LN_NM}/d' file.txt
I am using it to delete a line from file.txt.
But when this command is used without the variable it works fine.
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4Variables are not expanded in single quotes, use double quotes.– pLumoMar 25, 2020 at 8:31
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2Apart from using double quotes you also need to do away with the slashes.– Rakesh SharmaMar 25, 2020 at 9:09
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2 Answers
/regular expression/d will delete lines that match that regular expression (So if $LN_NUM is just a number like 5 or 18, every line with that number somewhere in it). If you want to instead delete the given line number:
sed "${LN_NM}d" file.txt
If you want to save the file after deleting that line from it, use ed, not sed:
ed -s file.txt <<EOF
${LN_NM}d
w
EOF
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You can use
sed -ito edit the file in place, instead of usinged. Mar 25, 2020 at 20:09 -
1@DavidConrad I can't recommend that;
sed -iis non standard and different implementations that support it as an extension have different behaviors - OS Xsed, for example, requires it to have an argument, while one is optional with GNUsed. Better to stay within POSIX especially when the asker doesn't say what OS they're using.– ShawnMar 25, 2020 at 20:22 -
As @plumo already mentioned, variables wont get substituted while using ' (single quotes)
Change your command by using " double-quotes, which should do the trick.
sed "/${LN_NM}d/" file.txt
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1That will delete lines containing the number in
$LN_NUM, not the exact line number...– ShawnMar 25, 2020 at 16:57 -
sorry, I misstyped the regular expression. I've updated the answer to correct it. Mar 26, 2020 at 11:40
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Uh, no. That won't even delete lines matching the regular expression, much less the line with the specific line number. Try it before you post. Mar 26, 2020 at 18:22