I have a script similar following one:


if [ $var == "ABC" ]
   echo True
   echo False

Above code does not work in Solaris Sparc and Solaris X64. It is showing == undefined. Above code works fine If I replace == with =.

Strange thing is If I ran above code without any change by following method it is working.

#bash test.sh

According to my understanding the script should not work even with bash, as at the top of the script I am using #!/bin/sh which does not support the == as the comparison operator.

Can anyone please explain why it does work when I am running the script as mentioned above.

Note: I am aware of that bash does recognize == and =.


The first line of the script is called the #! line (sometimes called the "shebang" line).

It is only used when a script is executed directly, as in



When you run an executable, the operating system looks at the first two bytes to tell what type of program it is.

When you run


the operating system sees that the first two bytes of ./test.sh are #!, so it knows the program is a script.

It reads the rest of the line to see which shell1 it should use to run the script. In this case, the rest of the line is /usr/bin/sh, so it runs /usr/bin/sh test.sh2.

When you run

bash test.sh

it finds bash in /usr/bin/bash3. It sees that the first two bytes of /usr/bin/bash are not #!, so it runs /usr/bin/bash test.sh without even looking at the first line of test.sh.

In both cases, sh and bash actually ignore the shebang line because any line beginning with # is a comment. The # only has this magic effect because of the operating system, not the shell.

More info:


  1. In fact, it can be any program, it doesn't have to be a shell.
  2. Actually more like execl("./test.sh", "/usr/bin/sh", "./test.sh", NULL).
  3. /bin/sh on most Linux systems, but the question was about Solaris.
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Running the script with bash (running bash test.sh) means that the script is interpreted with bash, not the Bourne shell (/bin/sh). That's why it works. Bash ignores the #!/bin/sh because it is a comment. It's only your OS's program loader that starts /bin/sh if you run the shell script without bash (running ./test.sh for example).

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