How can print a value, either 1, 2 or 3 (at random). My best guess failed:
#!/bin/bash
1 = "2 million"
2 = "1 million"
3 = "3 million"
print randomint(1,2,3)
5 Answers
To generate random numbers with bash use the $RANDOM internal Bash function:
arr[0]="2 million"
arr[1]="1 million"
arr[2]="3 million"
rand=$[ $RANDOM % 3 ]
echo ${arr[$rand]}
From bash manual for RANDOM:
Each time this parameter is referenced, a random integer between 0 and 32767 is generated. The sequence of random numbers may be initialized by assigning a value to RANDOM. If RANDOM is unset,it loses its special properties, even if it is subsequently reset.
3 Comments
Charles Duffy
$[ ] is a compatibility construct to support 1970s-era Bourne syntax; that construct is not found in more recent standards, and thus not guaranteed to be supported by more modern shells other than bash (which has historically included it). Since 1991, when POSIX sh was published, the standardized math construct has been $(( )), so this should be rand=$(( RANDOM % 3 )).Charles Duffy
I would also suggest quoting -- as in,
echo "${arr[$rand]}"; that way we won't have unexpected behavior with different values in IFS, or with array values that expand as globs. (For instance, if IFS=0123456789, then echo ${arr[$rand} without the quotes wouldn't print any number at all).
David Airapetyan
How about rand=$[ $RANDOM % ${#arr[@]} ] to avoid hardcoding 3?
Coreutils shuf
Present in Coreutils, this function works well if the strings don't contain newlines.
E.g. to pick a letter at random from a, b and c:
printf 'a\nb\nc\n' | shuf -n1
POSIX eval array emulation + RANDOM
Modifying Marty's eval technique to emulate arrays (which are non-POSIX):
a1=a
a2=b
a3=c
eval echo \$$(expr $RANDOM % 3 + 1)
This still leaves the RANDOM non-POSIX.
awk's rand() is a POSIX way to get around that.
answered Apr 28, 2015 at 9:01
Ciro Santilli OurBigBook.com
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2 Comments
Marty McGowan
what is "shuf"; linux? i don't see it on mac osx, and arrays are so ugly. see following answer
Ciro Santilli OurBigBook.com
@MartyMcGowan GNU non-POSIX as linked. Agree that arrays are ugly, but first option with shuf does not use the arrays. Agree that greater portability would be cool. I didn't know
set could set the arguments as you proposed, that's interesting.64 chars alpha numeric string
randomString32() {
index=0
str=""
for i in {a..z}; do arr[index]=$i; index=`expr ${index} + 1`; done
for i in {A..Z}; do arr[index]=$i; index=`expr ${index} + 1`; done
for i in {0..9}; do arr[index]=$i; index=`expr ${index} + 1`; done
for i in {1..64}; do str="$str${arr[$RANDOM%$index]}"; done
echo $str
}
1 Comment
Ciro Santilli OurBigBook.com
I believe this does not answer the question: OP wants to pick one out of 3 strings, not generate a completely random one. And
/dev/random is better for that.~.$ set -- "First Expression" Second "and Last"
~.$ eval echo \$$(expr $RANDOM % 3 + 1)
and Last
~.$
Comments
Want to corroborate using shuf from coreutils using the nice -n1 -e approach.
Example usage, for a random pick among the values a, b, c:
CHOICE=$(shuf -n1 -e a b c)
echo "choice: $CHOICE"
I looked at the balance for two samples sizes (1000, and 10000):
$ for lol in $(seq 1000); do shuf -n1 -e a b c; done > shufdata
$ less shufdata | sort | uniq -c
350 a
316 b
334 c
$ for lol in $(seq 10000); do shuf -n1 -e a b c; done > shufdata
$ less shufdata | sort | uniq -c
3315 a
3377 b
3308 c
Ref: https://www.gnu.org/software/coreutils/manual/html_node/shuf-invocation.html
answered Dec 10, 2020 at 13:30
Dr. Jan-Philip Gehrcke
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{1, 2, 3}1 = "2 million"lines supposed to mean? They aren't valid bash constructs.