There's also a very similar but simpler syntax for ternary conditionals in bash:

a=$(( b == 5 ? 123 : 321  ))

Here's a general solution, that

• works with string tests as well
• feels rather like an expression
• avoids any subtle side effects when the condition fails

Test with numerical comparison

a=$(if [ "$b" -eq 5 ]; then echo "$c"; else echo "$d"; fi)

Test with String comparison

a=$(if [ "$b" = "5" ]; then echo "$c"; else echo "$d"; fi)

You can use this if you want similar syntax

a=$(( $((b==5)) ? c : d ))

Some people have already presented some nice alternatives. I wanted to get the syntax as close as possible, so I wrote a function named ?.

This allows for the syntax:

[[ $x -eq 1 ]]; ? ./script1 : ./script2
# or
? '[[ $x -eq 1 ]]' ./script1 : ./script2

In both cases, the : is optional. All arguments that have spaces, the values must be quoted since it runs them with eval.

If the <then> or <else> clauses aren't commands, the function echos the proper value.

./script; ? Success! : "Failure :("

The function

?() {
  local lastRet=$?
  if [[ $1 == --help || $1 == -? ]]; then
    echo $'\e[37;1mUsage:\e[0m
  ? [<condition>] <then> [:] <else>

If \e[37;1m<then>\e[0m and/or \e[37;1m<else>\e[0m are not valid commands, then their values are
printed to stdOut, otherwise they are executed.  If \e[37;1m<condition>\e[0m is not
specified, evaluates the return code ($?) of the previous statement.

\e[37;1mExamples:\e[0m
  myVar=$(? "[[ $x -eq 1 ]] foo bar)
  \e[32;2m# myVar is set to "foo" if x is 1, else it is set to "bar"\e[0m

  ? "[[ $x = *foo* ]] "cat hello.txt" : "cat goodbye.txt"
  \e[32;2m# runs cat on "hello.txt" if x contains the word "foo", else runs cat on
  # "goodbye.txt"\e[0m

  ? "[[ $x -eq 1 ]] "./script1" "./script2"; ? "Succeeded!" "Failed :("
  \e[32;2m# If x = 1, runs script1, else script2.  If the run script succeeds, prints
  # "Succeeded!", else prints "failed".\e[0m'
    return
  elif ! [[ $# -eq 2 || $# -eq 3 || $# -eq 4 && $3 == ':' ]]; then
    1>&2 echo $'\e[37;1m?\e[0m requires 2 to 4 arguments

\e[37;1mUsage\e[0m: ? [<condition>] <then> [:] <else>
Run \e[37;1m? --help\e[0m for more details'
    return 1
  fi

  local cmd

  if [[ $# -eq 2 || $# -eq 3 && $2 == ':' ]]; then
    cmd="[[ $lastRet -eq 0 ]]"
  else
    cmd="$1"
    shift
  fi

  if [[ $2 == ':' ]]; then
    eval "set -- '$1' '$3'"
  fi

  local result=$(eval "$cmd" && echo "$1" || echo "$2")
  if command -v ${result[0]} &> /dev/null; then
    eval "${result[@]}"
  else
    echo "${result[@]}"
  fi
}

Obviously if you want the script to be shorter, you can remove the help text.

EDIT: I was unaware that ? acts as a placeholder character in a file name. Rather than matching any number of characters like *, it matches exactly one character. So, if you have a one-character file in your working directory, bash will try to run the filename as a command. I'm not sure how to get around this. I thought using command "?" ...args might work but, no dice.

Simplest ternary

brew list | grep -q bat && echo 'yes' || echo 'no'

This example will determine if you used homebrew to install bat or not yet

If true you will see "yes"

If false you will see "no"

I added the -q to suppress the grepped string output here, so you only see "yes" or "no"

Really the pattern you seek is this

doSomethingAndCheckTruth && echo 'yes' || echo 'no'

Tested with bash and zsh

This is much like Vladimir's fine answer. If your "ternary" is a case of "if true, string, if false, empty", then you can simply do:

$ c="it was five"
$ b=3
$ a="$([[ $b -eq 5 ]] && echo "$c")"
$ echo $a

$ b=5
$ a="$([[ $b -eq 5 ]] && echo "$c")"
$ echo $a
it was five

A string-oriented alternative, that uses an array:

spec=(IGNORE REPLACE)
for p in {13..15}; do
  echo "$p: ${spec[p==14]}";
done

which outputs:

13: IGNORE
14: REPLACE
15: IGNORE

to answer to : int a = (b == 5) ? c : d;

just write:

b=5
c=1
d=2
let a="(b==5)?c:d"

echo $a # 1

b=6;
c=1;
d=2;
let a="(b==5)?c:d"

echo $a # 2

remember that " expression " is equivalent to $(( expression ))

Two more answers

Here's some ways of thinking about this

bash integer variables

In addition to, dutCh, Vladimir and ghostdog74's corrects answers and because this question is regarding integer and tagged bash:

Is there a way to do something like this

int a = (b == 5) ? c : d;

There is a nice and proper way to work with integers under bash:

declare -i b=' RANDOM % 3 + 4 ' c=100 d=50 a='  b == 5 ? c : d '; echo $b '-->' $a

The output line from this command should by one of:

4 --> 50
5 --> 100
6 --> 50

Of course, declaring integer type of variable is to be done once:

declare -i a b c d
c=100 d=50 b=RANDOM%3+4
a=' b == 5 ? c : d '
echo $a $b
100 5
b=12 a=b==5?c:d
echo $a $b
50 12

Digression: Using a string as a math function:

mathString=' b == 5 ? c : d '
b=5 a=$mathString
echo $a $b
100 5

b=1 a=$mathString 
echo $a $b
50 1

Based on parameter expansion and indirection

Following answers from Brad Parks and druid62, here is a way not limited to integer:

c=50 d=100 ar=([5]=c)
read -p 'Enter B: ' b
e=${ar[b]:-d};echo ${!e}

• If b==5, then ar[b] is c and indirection do c is 50.
• Else ar[any value other than 5] is empty, so parameter expansion will default to d, where indirection give 100.

Same demo using an array instead of an integer

ternArrayDemo(){
    local -a c=(foo bar) d=(foo bar baz) e=(empty) ar=([5]=c [2]=d)
    local b=${ar[$1]:-e}
    b+=[@]      # For array indirection
    printf ' - %s\n' "${!b}"
}

Then

ternArrayDemo 0
 - empty
ternArrayDemo 2 
 - foo
 - bar
 - baz
ternArrayDemo 4
 - empty
ternArrayDemo 5
 - foo
 - bar
ternArrayDemo 6
 - empty

Or using associative arrays

ternAssocArrayDemo(){
     local -a c=(foo bar) d=(foo bar baz) e=(empty)
     local -A ar=([foo]=c[@] [bar]=d[@] [baz]=d[-1])
     local b=${ar[$1]:-e[@]}
     printf ' - %s\n' "${!b}"
}

Then

ternAssocArrayDemo hello
 - empty
ternAssocArrayDemo foo
 - foo
 - bar
ternAssocArrayDemo bar
 - foo
 - bar
 - baz
ternAssocArrayDemo baz
 - baz

The top answer [[ $b = 5 ]] && a="$c" || a="$d" should only be used if you are certain there will be no error after the &&, otherwise it will incorrectly excute the part after the ||.

To solve that problem I wrote a ternary function that behaves as it should and it even uses the ? and : operators:

Edit - new solution

Here is my new solution that does not use $IFS nor ev(a/i)l.

function executeCmds()
{
    declare s s1 s2 i j k
    declare -A cmdParts
    declare pIFS=$IFS
    IFS=$'\n'
    declare results=($(echo "$1" | grep -oP '{ .*? }'))
    IFS=$pIFS
    s="$1"
    for ((i=0; i < ${#results[@]}; i++)); do
        s="${s/${results[$i]}/'\0'}"
        results[$i]="${results[$i]:2:${#results[$i]}-3}"
        results[$i]=$(echo ${results[$i]%%";"*})
    done
    s="$s&&"
    let cmdParts[t]=0
    while :; do
        i=${cmdParts[t]}
        let cmdParts[$i,t]=0
        s1="${s%%"&&"*}||"
        while :; do
            j=${cmdParts[$i,t]}
            let cmdParts[$i,$j,t]=0
            s2="${s1%%"||"*};"
            while :; do
                cmdParts[$i,$j,${cmdParts[$i,$j,t]}]=$(echo ${s2%%";"*})
                s2=${s2#*";"}
                let cmdParts[$i,$j,t]++
                [[ $s2 ]] && continue
                break
            done
            s1=${s1#*"||"}
            let cmdParts[$i,t]++
            [[ $s1 ]] && continue
            break
        done
        let cmdParts[t]++
        s=${s#*"&&"}
        [[ $s ]] && continue
        break
    done
    declare lastError=0
    declare skipNext=false
    for ((i=0; i < ${cmdParts[t]}; i++ )) ; do
        let j=0
        while :; do
            let k=0
            while :; do
                if $skipNext; then
                    skipNext=false
                else
                    if [[ "${cmdParts[$i,$j,$k]}" == "\0" ]]; then
                         executeCmds "${results[0]}" && lastError=0 || lastError=1
                         results=("${results[@]:1}")
                    elif [[ "${cmdParts[$i,$j,$k]:0:1}" == "!" || "${cmdParts[$i,$j,$k]:0:1}" == "-" ]]; then
                        [ ${cmdParts[$i,$j,$k]} ] && lastError=0 || lastError=1
                    else
                        ${cmdParts[$i,$j,$k]}
                        lastError=$?
                    fi
                    if (( k+1 < cmdParts[$i,$j,t] )); then
                        skipNext=false
                    elif (( j+1 < cmdParts[$i,t] )); then
                        (( lastError==0 )) && skipNext=true || skipNext=false
                    elif (( i+1 < cmdParts[t] )); then
                        (( lastError==0 )) && skipNext=false || skipNext=true
                    fi
                fi
                let k++
                [[ $k<${cmdParts[$i,$j,t]} ]] || break
            done
            let j++
            [[ $j<${cmdParts[$i,t]} ]] || break
        done
    done
    return $lastError
}

function t()
{
    declare commands="$@"
    find="$(echo ?)"
    replace='?'
    commands="${commands/$find/$replace}"
    readarray -d '?' -t statement <<< "$commands"
    condition=${statement[0]}
    readarray -d ':' -t statement <<< "${statement[1]}"
    success="${statement[0]}"
    failure="${statement[1]}"
    executeCmds "$condition" || { executeCmds "$failure"; return; }
    executeCmds "$success"
}

executeCmds separates each command individually, apart from the ones that should be skipped due to the && and || operators. It uses [] whenever a command starts with ! or a flag.

There are two ways to pass commands to it:

1. Pass the individual commands unquoted but be sure to quote ;, &&, and || operators.

t ls / ? ls qqq '||' echo aaa : echo bbb '&&' ls qq

2. Pass all the commands quoted:

t 'ls /a ? ls qqq || echo aaa : echo bbb && ls qq'

NB I found no way to pass in && and || operators as parameters unquoted, as they are illegal characters for function names and aliases, and I found no way to override bash operators.

Old solution - uses ev(a/i)l

function t()
{
    pIFS=$IFS
    IFS="?"
    read condition success <<< "$@"
    IFS=":"
    read success failure <<< "$success"
    IFS=$pIFS
    eval "$condition" || { eval "$failure" ; return; }
    eval "$success"
}
t ls / ? ls qqq '||' echo aaa : echo bbb '&&' ls qq
t 'ls /a ? ls qqq || echo aaa : echo bbb && ls qq'

What about such approach:

# any your function
function check () {
    echo 'checking...';
    false; # <-- change this to true - to emulate successfull execution some function. Be aware in linux false and true is funciton it-self. see help false, for instance. Anyway you can replace check function with any function you wish.
}

# double check pattern
check && echo 'update' \
    || check || echo 'create'; 

See how conditional statements works in the RxJs (i.e. filter pipe). Yes, it is code duplication but more functional approach from my point of view.