CODEWITHSUNDEEP
bashunix
Argos
Argos

Reputation: 91

BASH: Use a String as file output

In a bash script I need to compare the first char of two Strings.

To do this, I use the head operator like this:

var1="foo"
var2="doo"
headVar1=$(head -c1 $var1)
headVar2=$(head -c1 $var2)

if [ $headVar1 == $headVar2 ]
  then
    #miau
fi

But the console says "head: cant open foo for reading: Doesnt exist the file or directorie" And the same with doo

Some help?

Thanks.

Upvotes: 0

Views: 90

Answers (3)

chepner
chepner

Reputation: 531215

A circuitous, but POSIX-compatible, solution:

var1="foo"
var2="doo"
headVar1=${var1%${var1#?}}
headVar2=${var2%${var2#?}}

if [ "$headVar1" = "$headVar2" ]
then
    #miau
fi

${var1#?} expands to the value of var1 minus its first character. That is used as the suffix to remove with ${var1%...}, leaving in the end just the first character of var1.

Upvotes: 0

choroba
choroba

Reputation: 241898

head interpreted foo as a filename. See man head on what options are available for the command.

To store command output in a variable, use command substitution:

headVar1=$(printf %s "$var1" | head -c1)

which could be shortened using a "here string":

headVar1=$(head -c1 <<< "$var1")

But parameter expansion is much faster in this case, as it doesn't spawn a subshell:

headVar1=${var1:0:1}

Upvotes: 3

Avinash Raj
Avinash Raj

Reputation: 174706

Your code must be,

var1="foo"
var2="doo"
headVar1=$(head -c1 <<<"$var1")
headVar2=$(head -c1 <<<"$var2")
if [[ "$headVar1" == "$headVar2" ]]
  then
    echo "It's same"
else
    echo "Not same"
fi

  • remove the space which exists next to equal sign (variable assignment part).

  • Use <<< to fed input from a variable to the corresponding function.

  • Variable names must be preceded by the dollar $ symbol.

Upvotes: 1

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