CODEWITHSUNDEEP
shell
nsane
nsane

Reputation: 1765

expr command not working in shell

Following is the code that I tried -

nisarg@nisarg-ThinkPad-T61:~$ export a=1
nisarg@nisarg-ThinkPad-T61:~$ export b=2
nisarg@nisarg-ThinkPad-T61:~$ echo $a
1
nisarg@nisarg-ThinkPad-T61:~$ echo $b
2
nisarg@nisarg-ThinkPad-T61:~$ echo 'expr $a + $b'
expr $a + $b

I even made sure there are spaces around + as they are the cause of most errors.

Why isn't this working?

Upvotes: 0

Views: 6072

Answers (2)

Vishala Ramasamy
Vishala Ramasamy

Reputation: 367

x=9
y=7
z=`expr $x + $y`
echo $z

Write the expression with spaces and surrounded with back-ticks (``).

Upvotes: 0

chepner
chepner

Reputation: 532053

The single quotes prevent $a and $b from being expanded, as well as expr from being called; you may be confusing single quotes with backquotes, which are the older syntax for command substitution. Use double quotes and $( ... ):

echo "$(expr $a + $b)"

The above code is equivalent to

expr $a + $b

so you only need the command substitution if you need to capture the output to assign to a variable or to embed the result in a longer string. Also, expr is unnecessary for arithmetic in a POSIX-compatible shell (i.e., almost any shell you are likely to be using). You can use an arithmetic expression $(( ... )) instead.

echo "$(( $a + $b ))"

Upvotes: 4

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