Bash: test mutual equality of multiple variables? - bash

Question

What is the right way to test if several variables are all equal?
if [[ $var1 = $var2 = $var3 ]] # syntax error
Is it necessary to write something like the following?
if [[ $var1 = $var2 && $var1 = $var3 && $var2 = $var3 ]] # cumbersome
if [[ $var1 = $var2 && $var2 = $var3 && $var3 = $var4 ]] # somewhat better
Unfortunately, the otherwise excellent Advanced Bash Scripting Guide and other online sources I could find don't provide such an example.
My particular motivation is to test if several directories all have the same number of files, using ls -1 $dir | wc -l to count files.
Note
"var1" etc. are example variables. I'm looking for a solution for arbitrary variable names, not just those with a predictable numeric ending.
Update
I've accepted Richo's answer, as it is the most general. However, I'm actually using Kyle's because it's the simplest and my inputs are guaranteed to avoid the caveat.
Thanks for the suggestions, everyone.

Answer 1

if you want to test equality of an arbitrary number of items (let's call them $item1-5, but they could be an array
st=0
for i in $item2 $item3 $item4 $item5; do
[ "$item1" = "$i" ]
st=$(( $? + st ))
done
if [ $st -eq 0 ]; then
echo "They were all the same"
fi

Answer 2

If they are single words you can get really cheap about it.
varUniqCount=`echo "${var1} ${var2} ${var3} ${var4}" | sort -u | wc -l`
if [ ${varUniqCount} -gt 1 ]; then
echo "Do not match"
fi

Answer 3

Transitive method of inspection.
#!/bin/bash
var1=10
var2=10
var3=10
if [[ ($var1 == $var2) && ($var2 == $var3) ]]; then
echo "yay"
else
echo "nay"
fi
Output:
[jaypal:~/Temp] ./s.sh
yay
Note:
Since you have stated in your question that your objective is to test several directories that have same number of files, I thought of the following solution. I know this isn't something you had request so please feel free to disregard it.
Step1:
Identify number of files in a given directory. This command will look inside sub-dirs too but that can be controlled using -depth option of find.
[jaypal:~/Temp] find . -type d -exec sh -c "printf {} && ls -1 {} | wc -l " \;
. 9
./Backup 7
./bash 2
./GTP 22
./GTP/ParserDump 11
./GTP/ParserDump/ParserDump 1
./perl 7
./perl/p1 2
./python 1
./ruby 0
./scripts 22
Step2:
This can be combined with Step1 as we are just redirecting the content to a file.
[jaypal:~/Temp] find . -type d -exec sh -c "printf {} && ls -1 {} | wc -l " \; > file.temp
Step3:
Using the following command we will look in the file.temp twice and it will give us a list of directories that have same number of files.
[jaypal:~/Temp] awk 'NR==FNR && a[$2]++ {b[$2];next} ($2 in b)' file.temp file.temp | sort -k2
./GTP/ParserDump/ParserDump 1
./python 1
./bash 2
./perl/p1 2
./Backup 7
./perl 7
./GTP 22
./scripts 22

Answer 4

(edited to include delimiters to fix the problem noted by Keith Thompson)
Treating the variable values as strings, you can concatenate them along with a suitable delimiter and do one comparison:
if [[ "$var1|$var2|$var3" = "$var1|$var1|$var1" ]]
I used = instead == because == isn't an equality comparison inside [[ ]], it is a pattern match.

Answer 5

For your specific case, this should work:
distinct_values=$(for dir in this_dir that_dir another_dir ; do ls -l "$dir" | wc -l ; done | uniq | wc -l)
if [ $distinct_values -eq 1 ] ; then
echo All the same
else
echo Not all the same
fi
Explanation:
ls -l "$dir" lists the files and subdirectories in the directory, one per line (omitting dot files).
Piping the output through wc -l gives you the number of files in the directory.
Doing that consecutively for each directory in the list gives you a list consisting of the number of files in each directory; if there are 7 in each, this gives 3 lines each consisting of the number 7
Piping that through uniq eliminates consecutive duplicate lines.
Piping that through wc -l gives you the number of distinct lines, which will be 1 if and only if all the directories contain the same number of files.
Note that the output of the 4th stage doesn't necessarily give you the number of distinct numbers of files in the directories; uniq only removes adjacent duplicates, so if the inputs are 7 6 7, the two 7s won't be merged. But it will merge all lines into 1 only if they're all the same.
This is the power of the Unix command line: putting small tools together to do interesting and useful things. (Show me a GUI that can do that!)
For values stored in variables, replace the first line by:
distinct_values=$(echo "$this_var" "$that_var" "$another_var" | fmt -1 | uniq | wc -l)
This assumes that the values of the variables don't contain spaces.