How to do a logical OR operation for integer comparison in shell scripting?

Question

I am trying to do a simple condition check, but it doesn't seem to work.

If $# is equal to 0 or is greater than 1 then say hello.

I have tried the following syntax with no success:

if [ "$#" == 0 -o "$#" > 1 ] ; then
 echo "hello"
fi

if [ "$#" == 0 ] || [ "$#" > 1 ] ; then
 echo "hello"
fi

They both work for me. Did you specify a shell in the *shebang* line? — Jason McCreary, Nov 06 '10 at 02:02
@Jason I actually forgot the shebang line, but I tested it with it just now and it didn't work. — Strawberry, Nov 06 '10 at 02:13
`>` is output redirection in sh/bash. Now you probably have a file named `1`. — mark4o, Nov 06 '10 at 02:14
For information on Bash comparisons, please see my answers to previous questions [here](http://stackoverflow.com/questions/2600281/what-is-the-difference-between-operator-and-in-bash/2601583#2601583) and [here](http://stackoverflow.com/questions/3869072/test-for-non-zero-length-string-in-bash-n-var-or-var/3870055#3870055). For additional information regarding brackets, double brackets and double parentheses, see my answer [here](http://stackoverflow.com/questions/2188199/bash-double-or-single-bracket-parentheses-curly-braces/2188369#2188369). — Dennis Williamson, Nov 06 '10 at 04:17
It doesn't work cause you mistype the compraison: use "$#" == "0" or $# -eq 0 — ETech, Sep 18 '16 at 06:32

score 1031 · Accepted Answer · edited Apr 26 '18 at 10:40

1031

This should work:

#!/bin/bash

if [ "$#" -eq 0 ] || [ "$#" -gt 1 ] ; then
    echo "hello"
fi

I'm not sure if this is different in other shells but if you wish to use <, >, you need to put them inside double parenthesis like so:

if (("$#" > 1))
 ...

edited Apr 26 '18 at 10:40

JohannesM

213
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14

answered Nov 06 '10 at 02:03

Coding District

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I'm not sure if it's different in another shell but in bash, if you wish to use > or <, you have to put them in double parenthesis like so: (("$a" < "$b")) – Coding District Nov 06 '10 at 02:13
1

@Doug: It's not that unix doesn't use them, it's that bash and all the other shells I know use them for input/output redirection. – Cascabel Nov 06 '10 at 02:28

score 58 · Answer 2 · answered Nov 06 '10 at 02:01

58

This code works for me:

#!/bin/sh

argc=$#
echo $argc
if [ $argc -eq 0 -o $argc -eq 1 ]; then
  echo "foo"
else
  echo "bar"
fi

I don't think sh supports "==". Use "=" to compare strings and -eq to compare ints.

man test

for more details.

answered Nov 06 '10 at 02:01

jbremnant

894
6
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What is the option for greater than? Where's the official documentation for tihs? – Strawberry Nov 06 '10 at 02:07
3

Should be `-gt` for greater than. Or just replace it all with `[ $# -ne 1 ]`. – mark4o Nov 06 '10 at 02:08
Greater than is -gt, see my answer. The official documentation is in man test as jbremnant has pointed out. – Coding District Nov 06 '10 at 02:09
Just as an fyi for others, depending on your shell, most support == (now a days) as an comparison operator, however most of the time it is the same as the = operator. I would imagine that if you are using -gt and -ne for comparisons that it would be better practice to use -eq for == or = to keep your scripting style consistent. Happy Bashing :) – jkdba Nov 03 '15 at 13:58

luca76 · Answer 3 · 2015-06-10T15:25:57.110

39

If you are using the bash exit code status $? as variable, it's better to do this:

if [ $? -eq 4 -o $? -eq 8 ] ; then  
   echo "..."
fi

Because if you do:

if [ $? -eq 4 ] || [ $? -eq 8 ] ; then

The left part of the OR alters the $? variable, so the right part of the OR doesn't have the original $? value.

edited Jun 10 '15 at 15:25

answered May 11 '15 at 09:45

luca76

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$# returns the number of arguments passed to the script. Useful for checking correct usage. It doesn't seem like the asker is using exit codes. – Centimane Aug 19 '15 at 11:53

score 31 · Answer 4 · answered May 02 '16 at 15:17

31

Sometimes you need to use double brackets, otherwise you get an error like too many arguments

if [[ $OUTMERGE == *"fatal"* ]] || [[ $OUTMERGE == *"Aborting"* ]]
  then
fi

answered May 02 '16 at 15:17

TechNikh

541
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This is useful because it's the only thing here that I see showing an example of non-integer comparisons, which are slightly different in syntax. – Christopher Hunter Mar 20 '19 at 00:29
Also, a space is required after "fatal"* . and "Aborting"* before closing ] – Rohit Gaikwad Aug 03 '20 at 10:28

score 14 · Answer 5 · edited Jun 07 '18 at 04:38

14

If a bash script

If [[ $input -gt number  ||  $input  -lt number  ]]
then 
    echo .........
else
    echo .........

fi

exit

edited Jun 07 '18 at 04:38

Mohammad Kanan

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answered Jun 07 '18 at 04:17

Peprah David

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2

score 8 · Answer 6 · answered Nov 06 '10 at 01:58

8

have you tried something like this:

if [ $# -eq 0 ] || [ $# -gt 1 ] 
then
 echo "$#"
fi

answered Nov 06 '10 at 01:58

John Boker

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17
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Yes, I have. It `echo`s hello even when I have a single argument. – Strawberry Nov 06 '10 at 02:04
The second `$#` might be the return value of the first test? – luckydonald Jun 17 '18 at 17:00

fedorqui · Answer 7 · 2020-05-14T10:17:32.143

6

From Bash Reference Manual → 3.4.2 Special Parameters

#
($#) Expands to the number of positional parameters in decimal.

Therefore, $# will always be either 0 or a bigger integer.

So if you want to do something whenever $# is either 0 or bigger than 1, you just have to check if $# is or is not 1:

[ $# -eq 1 ] && echo "1 positional param" || echo "0 or more than 1"

This uses the syntax:

[ condition ] && {things if true} || {things if false}

edited May 14 '20 at 10:17

answered Nov 18 '15 at 22:21

fedorqui

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in bash you can do something like: `[[ -n $A ]] && echo 1 || echo 2` – premek.v Jan 16 '17 at 01:19
@premek.v thanks for the comment. My answer was very badly explained, I just edited it in the hope that it sheds more light to the topic. – fedorqui Jan 16 '17 at 09:57

score 1 · Answer 8 · answered Jan 08 '19 at 10:32

And in Bash

 line1=`tail -3 /opt/Scripts/wowzaDataSync.log | grep "AmazonHttpClient" | head -1`
 vpid=`ps -ef|  grep wowzaDataSync | grep -v grep  | awk '{print $2}'`
 echo "-------->"${line1}
    if [ -z $line1 ] && [ ! -z $vpid ]
    then
            echo `date --date "NOW" +%Y-%m-%d` `date --date "NOW" +%H:%M:%S` :: 
            "Process Is Working Fine"
    else
            echo `date --date "NOW" +%Y-%m-%d` `date --date "NOW" +%H:%M:%S` :: 
            "Prcess Hanging Due To Exception With PID :"${pid}
   fi

OR in Bash

line1=`tail -3 /opt/Scripts/wowzaDataSync.log | grep "AmazonHttpClient" | head -1`
vpid=`ps -ef|  grep wowzaDataSync | grep -v grep  | awk '{print $2}'`
echo "-------->"${line1}
   if [ -z $line1 ] || [ ! -z $vpid ]
    then
            echo `date --date "NOW" +%Y-%m-%d` `date --date "NOW" +%H:%M:%S` :: 
            "Process Is Working Fine"
    else
            echo `date --date "NOW" +%Y-%m-%d` `date --date "NOW" +%H:%M:%S` :: 
            "Prcess Hanging Due To Exception With PID :"${pid}
  fi

How to do a logical OR operation for integer comparison in shell scripting?

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