Compare a string using sh shell

Question

I am using SH shell and I am trying to compare a string with a variable's value but the if condition is always execute to true. Why?

Here is some code:

Sourcesystem="ABC"

if [ "$Sourcesystem" -eq 'XYZ' ]; then 
    echo "Sourcesystem Matched" 
else
    echo "Sourcesystem is NOT Matched $Sourcesystem"  
fi;

echo Sourcesystem Value is  $Sourcesystem ;

Even this is not working:

Sourcesystem="ABC"

if [ 'XYZ' -eq "$Sourcesystem" ]; then 
    echo "Sourcesystem Matched" 
else
    echo "Sourcesystem is NOT Matched $Sourcesystem"  
fi;

echo Sourcesystem Value is  $Sourcesystem ;

Secondly, can we match this with a NULL or empty string?

First in Bourne shell you don't need the extra ';' When I test run the script in Bourne shell, the if condition is false. It will first give an warning: [: ABC: integer expression expected. The output is: "Sourcesystem is NOT Matched ABC". As commented by others, -eq is used for integer comparisons. Use a single equal sign for string comparison in Bourne shell (#!/bin/sh). Your shell should have corrected you in the first place. — Kemin Zhou, Mar 21 '16 at 03:52
Voting to reopen. The cited dups are for bash shell, not the anemic sh shell which is sometimes a Posix shell or Dash. — jww, Jan 18 '19 at 10:55
Agreed and so voted. `sh` and `bash` bear the same relationship as `C` and `C++`. Even though code written for the first is valid in the second, answers for the second can't be trusted to work in the first. — btilly, Apr 17 '20 at 17:27

score 364 · Answer 1 · edited May 05 '15 at 21:08

364

You should use the = operator for string comparison:

Sourcesystem="ABC"

if [ "$Sourcesystem" = "XYZ" ]; then 
    echo "Sourcesystem Matched" 
else
    echo "Sourcesystem is NOT Matched $Sourcesystem"  
fi;

man test says that you use -z to match for empty strings.

edited May 05 '15 at 21:08

the Tin Man

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answered Jun 01 '12 at 11:24

Mithrandir

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4

It is not necessary to quote `ABC` or `XYZ`. – ceving Feb 12 '16 at 15:09
49

If your variable might have spaces in it then quoting is necessary. – William Everett Jan 11 '17 at 19:07
1

Adjusted the example to make that part clearer @WilliamEverett. – Per Lundberg Jul 28 '17 at 08:54
1

This method doesn't work with sh nor bash (macOS 11.2) if both strings contain multiple lines, where the first line is equal but further lines are different - then I get always true for a `=` test. With macOS' new zsh, however, I can even leave the quotes out, as in `[ $a = $b ]`, and get the correct result for multi-line strings. – Thomas Tempelmann Feb 10 '21 at 15:33
1

@Thomas - the OP question is specifically about `sh` not bash or zsh. OP examples would also never me multi-line strings. Multi-line strings should probably take a different approach rather than rely on a feature of zsh, unless you are working in an exclusively zsh environment. Targeting `sh` usually means you need high portability because bash and/or zsh isn't available in all of your environments. I'm on macOS and could target zsh, but then when my scripts are moved to linux system over which I have no control they will fail due to zsh not being present. – Stephen P Feb 24 '21 at 00:14

score 95 · Answer 2 · answered Jun 01 '12 at 11:24

95

-eq is used to compare integers. Use = instead.

answered Jun 01 '12 at 11:24

Piotr Praszmo

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And pay attention to not use double equal "==" – Rodrigo Caballero Jul 18 '18 at 14:16

score 53 · Answer 3 · answered May 02 '17 at 14:37

53

eq is used to compare integers use equal '=' instead , example:

if [ 'AAA' = 'ABC' ];
then 
    echo "the same" 
else 
    echo "not the same"
fi

good luck

answered May 02 '17 at 14:37

Qign20

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Note: if you're comparing variables, make sure you use `"$VAR"` and not simply `$VAR` – Sridhar Sarnobat Jul 29 '20 at 18:48
Also note that if you are comparing a variable to a string `[ $(VAR) = "ABC" ]` – Jesse H. Oct 05 '22 at 17:14

score 32 · Answer 4 · edited Feb 03 '21 at 22:50

32

I had this same problem, do this

if [ 'xyz' = 'abc' ]; then
  echo "match"
fi

Notice the whitespace. It is important that you use a whitespace in this case after and before the = sign.

Check out "Other Comparison Operators".

edited Feb 03 '21 at 22:50

Thomas Tempelmann

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answered Sep 24 '14 at 06:55

Eswar Yaganti

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in Dockerfile: /bin/sh: 1: [: =: unexpected operator – holms Apr 12 '17 at 23:35
You linked to documentation for bash, the OP asked about /bin/sh. – Dan Tenenbaum Oct 20 '22 at 23:57

codaddict · Answer 5 · 2012-06-04T05:27:26.590

12

-eq is the shell comparison operator for comparing integers. For comparing strings you need to use =.

edited Jun 04 '12 at 05:27

answered Jun 01 '12 at 11:25

codaddict

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score 3 · Answer 6 · edited Mar 06 '13 at 16:08

3

-eq is a mathematical comparison operator. I've never used it for string comparison, relying on == and != for compares.

if [ 'XYZ' == 'ABC' ]; then   # Double equal to will work in Linux but not on HPUX boxes it should be if [ 'XYZ' = 'ABC' ] which will work on both
  echo "Match"
else
  echo "No Match"
fi

edited Mar 06 '13 at 16:08

Shaik Md

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answered Jun 01 '12 at 11:25

Jason

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Note that the operator `==` does not work on every shell. `=` is the correct operator to use in order to compare strings, and `==` is sometimes a synonym. – Omer Dagan Mar 08 '15 at 12:26
This answer is **wrong** for /bin/sh scripts and will fail. On macOS, the "test" command (also available as "[") treats "="" as "=". On Linux it doesn't. – neuhaus Oct 21 '21 at 08:55

score 3 · Answer 7 · answered Jun 01 '12 at 14:10

3

Of the 4 shells that I've tested, ABC -eq XYZ evaluates to true in the test builtin for zsh and ksh. The expression evaluates to false under /usr/bin/test and the builtins for dash and bash. In ksh and zsh, the strings are converted to numerical values and are equal since they are both 0. IMO, the behavior of the builtins for ksh and zsh is incorrect, but the spec for test is ambiguous on this.

answered Jun 01 '12 at 14:10

William Pursell

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Thanks for testing. That's why Bourne shell is popular. – Kemin Zhou Mar 21 '16 at 03:57
**zsh** clearly outputs _: integer expression expected_ after using **[** or builtin **test**. Maybe you are forcing *[[* which evaluates both as 0 as strings are **not** significant integers. – Mario G Jul 02 '19 at 20:57
@code933k Which version? I wouldn't be surprised if the behavior has changed. – William Pursell Jul 02 '19 at 21:01
@WilliamPursell zsh 5.7.1 – Mario G Jul 02 '19 at 21:02

Compare a string using sh shell

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