Command-line expression evaluator
The expr utility evaluates expressions and writes the result on standard output.
See the FreeBSD Man page.
Questions tagged [expr]
102 questions
14
votes
3 answers
Multiplication with expr in shell script
I am making a basic calculator to add, subtract, multiply, and divide.
Addition works, but not multiplication. When I attempt to multiply, I get the "You did not run the program correctly" response:
$ ./calculator 4 + 5
9
$ ./calculator 4 * 5
You…
Alex Wolfe
- 141
- 1
- 1
- 3
10
votes
2 answers
MongoDB find expr with multiple eq
This query which should filter results by the month seems to be working fine. But I can't figure out how to add a year filter as well.
db.collection.find({
"$expr": {
"$eq": [{ "$month": "$timestamp" }, 12]
}
});
I tried to come up with…
user4123355
6
votes
2 answers
Replace parentheses in pyspark with replace_regex
+---+------------+
| A| B|
+---+------------+
| x1| [s1]|
| x2| [s2 (A2)]|
| x3| [s3 (A3)]|
| x4| [s4 (A4)]|
| x5| [s5 (A5)]|
| x6| [s6 (A6)]|
+---+------------+
The desired result:
+---+------------+-------+
|A |B …
Sadek
- 127
- 1
- 8
4
votes
4 answers
select column names containing string programmatically
Given a data frame like:
df <- data.frame(z_a = 1:2,
z_b = 1:2,
y_a = 3:4,
y_b = 3:4)
I can select columns names that contain a character with:
library(dplyr)
df %>% select(contains("a"),…
CPak
- 13,260
- 3
- 30
- 48
3
votes
3 answers
Why does Tcl expr consider some number as "empty" while it's really not empty?
Problem Statement
I'm importing a set of coordinate from an unknown source, which I don't have privilege to look into.
set yMin [lindex [lindex $bbox 0] 1]
puts "yMin: <$yMin>"
It works normally.
yMin: <-6.149999999999999e-02>
The brackets are…
Zureas
- 53
- 5
3
votes
2 answers
Why does expr fail when matching a single 0
The following command works:
$ expr 1 : '\(.\)' || echo fail
1
When trying to match the string "0" the command fails, e.g. $? == 1:
$ expr 0 : '\(.\)' || echo fail
fail
The man page says:
Exit status is 0 if EXPRESSION is neither null nor 0
But,…
Dag Lövenvald
- 33
- 3
3
votes
2 answers
Use $regex inside $expr in mongodb aggregation
My doc looks as follows
doc = {
name: 'abc',
age:20
}
and my query looks like
{ $expr: {$and:[{ $gt:[ "$age", 10 ] },
{ $regex:["$name",'ab']}
]
}
} }
But it's not working and I get an…
ganesh
- 2,024
- 16
- 17
3
votes
2 answers
How to use expr inside if statement?
I have not managed to understand how to embed expr in other constructs.
I can easily type
set i {1 2 3}
expr {[llength $i]} #result is 3
However after long research I have not managed to find a way to put that inside if
if {"magic tcl code with…
Draif Kroneg
- 743
- 13
- 34
3
votes
2 answers
Equavalent operation of mathematica in python
Suppose that:
h=[1,2,3]
There is operation N[expr] in Mathematica that gives us:
N[h[0]]=1, N[h[1]]=2, N[h[2]]=3
and for example N[h[6]]=0, is something like this in Python?
BASU
- 49
- 1
- 3
3
votes
2 answers
What is the difference between $(()) and expr?
What is the main difference between $(()) and expr in Unix-Like systems?
SuckLips
- 55
- 1
- 11
3
votes
1 answer
calling a function using expr during an LLDB session
I'm trying to get a better grasp of LLDB and am currently stuck trying to call a locally defined function (using LLDB's expr) while debugging some code. For the sake of simplicity, lets consider this toy code:
testing_lldb.c:
unsigned long…
banach-space
- 1,781
- 1
- 12
- 27
3
votes
2 answers
Lazy regex operator doesn't work in bash
echo "$(expr "title: Purple Haze artist: Jimi Hendrix" : 'title:\s*\(.*\?\)\s*artist.*' )"
prints
Purple Haze
With the trailing whitespace, even though I am using the ? lazy operator.
I've tested this on https://regex101.com/…
texasflood
- 1,571
- 1
- 13
- 22
3
votes
2 answers
Syntax error expr
Why does the following returning a syntax error:
stringZ=abcABC123ABCabc
echo `expr match "$stringZ" 'abc[A-Z]*.2'`
This works on my ubuntu machine but when I try it on my mac running OS X 10.9.4 I get expr: syntax error?
rudolph9
- 8,021
- 9
- 50
- 80
2
votes
1 answer
Partially evaluate an expression in R
Sorry.
I have an expression:
#x^p
I want to evaluate this for a given p.
p -> 0
# 1
p -> 1
#x
p -> 2
#x^2
p -> 3
#x^3
p -> -1
#x^-1
If I type in:
p -> 1
eval(p)
#1
BUT
p -> 1
eval(x^p)
Gives the error:
#Error in eval(x^p) : object 'x' not…
heh
- 23
- 4
2
votes
1 answer
How to parse a formula in Pyspark?
i am new in Pyspark and I have some doubts.
I have a df like this:
+---+---+-------+
| a1| a2|formula|
+---+---+-------+
| 18| 12| a1+a2|
| 11| 1| a1-a2|
+---+---+-------+
I'm trying to parse the column 'formula' to create a new column with the…
DaniloP
- 29
- 1