Store output in variable & use variable in command

Question

I am trying to run a command and store it in a variable.

length=`last | grep foouser | wc -l`

It works fine but when I add a variable to the command it breaks.

value=$1
length=`last | grep $value | wc -l`

How can I get this second example to work by acceptomg a variable?

What, exactly, breaks? Also, you probably want to use $value in place of $1 in the grep command. — chepner
– chepner, Commented Jul 15, 2013 at 13:46

glenn jackman · Accepted Answer · 2013-07-15 15:31:44Z

4

You don't actually need wc:

length=$(last | grep -c "$value")

You could improve the variable names

num_logins=$(last | grep -c "$username")

answered Jul 15, 2013 at 15:31

glenn jackman

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Benoit · Accepted Answer · 2013-07-15 13:30:42Z

4

You should quote your variables properly. If they contain spaces your script might break:

value="$1"
length="$(last | grep "$value" | wc -l)"

answered Jul 15, 2013 at 13:30

Benoit

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4 Comments

chepner Over a year ago

Quoting $value as the argument to grep is important. Quoting the RHS of the two assignments is less so; word-splitting isn't performed, so I'm not sure there's any problem with leaving them unquoted (although it doesn't hurt to quote them, either).

ojhawkins Over a year ago

still not luck, I am entering value="foouser" /n length="$(last | grep "$value" | wc -l)" then trying to echo $lenght and it returns nothing @Benoit @chepner

chepner Over a year ago

You typed lenght by accident here. Are you mistyping at your terminal as well?

Léo Léopold Hertz 준영 Over a year ago

I think you should use brackets properly "${value}".

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