expr - evaluate arguments as an expression
The expr utility shall evaluate an expression and write the result to standard output.
Questions tagged [expr]
25 questions
77
votes
7 answers
Parenthesis in expr arithmetic: 3 * (2 + 1)
expr does not seem to like parenthesis (used in mathematics to explicit operator priority):
expr 3 * (2 + 1)
bash: syntax error near unexpected token `('
How to express operator priority in bash?
Nicolas Raoul
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16
votes
3 answers
Using expr, $(()), (())
In shell script we can substitute expr $a*$b with $(($a+$b)).
But why not just with (($a+$b)), because in any resource it is written that (()) is for integer computation.
So we use $(()) when there are variables instead of integer values do we?…
Stranger
- 187
- 1
- 1
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8
votes
2 answers
How to read string as hex number in bash?
I have the bash line:
expr substr $SUPERBLOCK 64 8
Which is return to me string line:
00080000
I know that this is, actually, a 0x00080000 in little-endian. Is there a way to create integer-variable from it in bash in big-endian like 0x80000?
DenisNovac
- 285
- 2
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- 10
4
votes
3 answers
Convert only parts of a filename to uppercase
In a shell script program, I need to convert the filenames to uppercase if the converted filename does not already exist. In this particular case I need to change only the basename to uppercase leaving the extension (if any) as it is.
My idea of…
Esha
- 183
- 6
3
votes
1 answer
Understanding of the regexp match feature of the expr utility
Could anyone help me to understand how the regex match works with the expr utility? I've read its man page and below is an excerpt:
STRING : REGEXP
anchored pattern match of REGEXP in STRING
But I can't understand how it works. I did some…
Fajela Tajkiya
- 965
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- 15
3
votes
3 answers
Set a variable to the result of a division and subtraction command
I am trying to get the difference of 2 dates in epoch form and convert the number back to days:
EXPIRYEPOCH=$(date --date="$EXPIRYDATE" +%s)
TODAYEPOCH=$(date --date="$TODAYSDATE" +%s)
DAYSLEFT=$(expr ($EXPIRYEPOCH - $TODAYEPOCH) / 86400 )
The…
Kahn
- 1,652
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- 36
2
votes
2 answers
How to add mathematically the results of two commands in Linux
In a Debian Linux shell, I am trying to add the results of two separate commands so that I know the sum of both.
I already tried:
echo $(expr $(du -sh /srv/mysql) + $(du -sh /srv/www))
and variations of it.
It's returning: expr:
"syntax error:…
davidman77
- 121
- 3
2
votes
1 answer
What does this expr do in a shell script?
What does the following do exactly?
newProg=`expr "${newProg}" : ".* -> \(.*\)$"`
if expr "x${newProg}" : 'x/' >/dev/null; then
prog="${newProg}"
else
progdir=`dirname "${prog}"`
prog="${progdir}/${newProg}"
fi …
Jim
- 9,750
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2
votes
1 answer
expr and variables
How do I run the script: ./script.sh 1 \* 2
Eventually: ./script.sh 1 '*' 2
How does my script look like:
args="$@" # the first line of the script
result=$(($args))
echo "$args = $result"
Does it work: yes
What I want to achieve: I want to use…
SantaXL
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2
votes
1 answer
arithmetic operation with expr
I am doing add operation as
#!/bin/sh
a=10
b=20
c='expr $a + $b'
echo "$c"
echo "$a"
echo "$b"
but it is showing output as
expr $a + $b
10
20
what is wrong with expr
user183924
- 21
- 2
2
votes
3 answers
Proper type casting in a shell script for use with while loop and modulus
I am trying to write a script to get a random, even hex number. I have found the the openssl command has a convenient option for creating random hex numbers. Unfortunately, I need it to be even and my script has a type casting error somewhere. Bash…
resu
- 133
- 1
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2
votes
2 answers
Meaning of `expr "hello" : "\([a-z]*\)"`?
I need a explanation of why:
$test=`expr "hello" : "\([a-z]*\)"`; echo $test
would print out hello, where as:
$test=`expr "hello" : "hel"`; echo $test
would return the number of characters matching.
And also:
$ test=`expr "hello123there" :…
夢のの夢
- 491
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1
vote
1 answer
awk arithmetic differs from expr
There are some contrast output between awk arithmetic and expr.
Example
expr 11111111111111111111 / 22
gives
505050505050505050
but with awk:
echo '11111111111111111111' | awk '{q=$1/22;;print q}'
gives
505050505050505024
Can somebody explain?
user305910
1
vote
2 answers
Echo calculation to text file
I am working on a project to calculate my overtime at work with a shell script. I have two inputs and want to find if my number is over 800 = 8 hours;
if it is bigger, then it has to print out the result to my text file.
It has to print out my…
peter
- 17
- 4
1
vote
2 answers
shell - using expr “multiplication table”
I'm learning shell to create a multiplication table, I write code like that:
#!/ in/bash
for i in 1 2 3 4 5 6 7 8 9
do
for j in 1 2 3 4 5 6 7 8 9
do
if [ $j -le $i ]
then
echo -ne…
Lost Vanity
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