CODEWITHSUNDEEP
bashshellunix
user389955
user389955

Reputation: 10467

How to represent multiple conditions in a shell if statement?

I want to represent multiple conditions like this:

if [ ( $g -eq 1 -a "$c" = "123" ) -o ( $g -eq 2 -a "$c" = "456" ) ]   
then  
    echo abc;  
else  
    echo efg;   
fi

but when I execute the script, it shows

syntax error at line 15: `[' unexpected,

where line 15 is the one showing if ....

What is wrong with this condition? I guess something is wrong with the ().

Upvotes: 415

Views: 1191681

Answers (8)

Ashan Priyadarshana
Ashan Priyadarshana

Reputation: 3629

In Bash, you can use the following technique for string comparison

if [ $var OP "val" ]; then
    echo "statements"
fi

Example:

var="something"
if [ $var != "otherthing" ] && [ $var != "everything" ] && [ $var != "allthings" ]; then
    echo "this will be printed"
else
    echo "this will not be printed"
fi

Upvotes: 10

ghostdog74
ghostdog74

Reputation: 342433

g=3
c=133
([ "$g$c" = "1123" ] || [ "$g$c" = "2456" ]) && echo "abc" || echo "efg"

Output:

efg

g=1
c=123
([ "$g$c" = "1123" ] || [ "$g$c" = "2456" ]) && echo "abc" || echo "efg"

Output:

abc

Upvotes: 6

Yordan Georgiev
Yordan Georgiev

Reputation: 5430

You can also chain more than two conditions:

if [ \( "$1" = '--usage' \) -o \( "$1" = '' \) -o \( "$1" = '--help' \) ]
then
   printf "\033[2J";printf "\033[0;0H"
   cat << EOF_PRINT_USAGE

   $0 - Purpose: upsert qto http json data to postgres db

   USAGE EXAMPLE:

   $0 -a foo -a bar



EOF_PRINT_USAGE
   exit 1
fi

Upvotes: -2

Debjyoti Banerjee
Debjyoti Banerjee

Reputation: 1

#!/bin/bash

current_usage=$( df -h | grep 'gfsvg-gfslv' | awk {'print $5'} )
echo $current_usage
critical_usage=6%
warning_usage=3%

if [[ ${current_usage%?} -lt ${warning_usage%?} ]]; then
echo OK current usage is $current_usage
elif [[ ${current_usage%?} -ge ${warning_usage%?} ]] && [[ ${current_usage%?} -lt ${critical_usage%?} ]]; then
echo Warning $current_usage
else
echo Critical $current_usage
fi

Upvotes: 0

sunitha
sunitha

Reputation: 1528

Using /bin/bash the following will work:

if [ "$option" = "Y" ] || [ "$option" = "y" ]; then
    echo "Entered $option"
fi

Upvotes: 55

orkoden
orkoden

Reputation: 20006

Be careful if you have spaces in your string variables and you check for existence. Be sure to quote them properly.

if [ ! "${somepath}" ] || [ ! "${otherstring}" ] || [ ! "${barstring}" ] ; then

Upvotes: 11

Jonathan Leffler
Jonathan Leffler

Reputation: 754050

Classic technique (escape metacharacters):

if [ \( "$g" -eq 1 -a "$c" = "123" \) -o \( "$g" -eq 2 -a "$c" = "456" \) ]
then echo abc
else echo efg
fi

I've enclosed the references to $g in double quotes; that's good practice, in general. Strictly, the parentheses aren't needed because the precedence of -a and -o makes it correct even without them.

Note that the -a and -o operators are part of the POSIX specification for test, aka [, mainly for backwards compatibility (since they were a part of test in 7th Edition UNIX, for example), but they are explicitly marked as 'obsolescent' by POSIX. Bash (see conditional expressions) seems to preempt the classic and POSIX meanings for -a and -o with its own alternative operators that take arguments.

With some care, you can use the more modern [[ operator, but be aware that the versions in Bash and Korn Shell (for example) need not be identical.

for g in 1 2 3
do
    for c in 123 456 789
    do
        if [[ ( "$g" -eq 1 && "$c" = "123" ) || ( "$g" -eq 2 && "$c" = "456" ) ]]
        then echo "g = $g; c = $c; true"
        else echo "g = $g; c = $c; false"
        fi
    done
done

Example run, using Bash 3.2.57 on Mac OS X:

g = 1; c = 123; true
g = 1; c = 456; false
g = 1; c = 789; false
g = 2; c = 123; false
g = 2; c = 456; true
g = 2; c = 789; false
g = 3; c = 123; false
g = 3; c = 456; false
g = 3; c = 789; false

You don't need to quote the variables in [[ as you do with [ because it is not a separate command in the same way that [ is.

Isn't it a classic question?

I would have thought so. However, there is another alternative, namely:

if [ "$g" -eq 1 -a "$c" = "123" ] || [ "$g" -eq 2 -a "$c" = "456" ]
then echo abc
else echo efg
fi

Indeed, if you read the 'portable shell' guidelines for the autoconf tool or related packages, this notation — using '||' and '&&' — is what they recommend. I suppose you could even go so far as:

if [ "$g" -eq 1 ] && [ "$c" = "123" ]
then echo abc
elif [ "$g" -eq 2 ] && [ "$c" = "456" ]
then echo abc
else echo efg
fi

Where the actions are as trivial as echoing, this isn't bad. When the action block to be repeated is multiple lines, the repetition is too painful and one of the earlier versions is preferable — or you need to wrap the actions into a function that is invoked in the different then blocks.

Upvotes: 489

Dennis Williamson
Dennis Williamson

Reputation: 360143

In Bash:

if [[ ( $g == 1 && $c == 123 ) || ( $g == 2 && $c == 456 ) ]]

Upvotes: 235

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