Bash Script what does bin bash mean

Question

In bash script  what does    bin bash at the 1st line mean    UPDATE  Is there a difference between    bin bash and    bin sh

User · Answer

When the first characters in a script are #!, that is called the shebang. If your file starts with #!/path/to/something the standard is to run something and pass the rest of the file to that program as an input.

With that said, the difference between #!/bin/bash, #!/bin/sh, or even #!/bin/zsh is whether the bash, sh, or zsh programs are used to interpret the rest of the file. bash and sh are just different programs, traditionally. On some Linux systems they are two copies of the same program. On other Linux systems, sh is a link to dash, and on traditional Unix systems (Solaris, Irix, etc) bash is usually a completely different program from sh.

Of course, the rest of the line doesn't have to end in sh. It could just as well be #!/usr/bin/python, #!/usr/bin/perl, or even #!/usr/local/bin/my_own_scripting_language.

User · Answer

In bash script  what does    bin bash at the 1st line mean    In Linux system  we have shell which interprets our UNIX commands  Now there are a number of shell in Unix system  Among them  there is a shell called bash which is very very common Linux and it has a long history  This is a by default shell in Linux   When you write a script  collection of unix commands and so on  you have a option to specify which shell it can be used  Generally you can specify which shell it wold be by using Shebang Yes that s what it s name     So if you    bin bash in the top of your scripts then you are telling your system to use bash as a default shell   Now coming to your second question  Is there a difference between    bin bash and    bin sh    The answer is Yes  When you tell    bin bash then you are telling your environment  os to use bash as a command interpreter  This is hard coded thing   Every system has its own shell which the system will use to execute its own system scripts  This system shell can be vary from OS to OS most of the time it will be bash  Ubuntu recently using dash as default system shell   When you specify    bin sh then system will use it s internal system shell to interpreting your shell scripts   Visit this link for further information where I have explained this topic    Hope this will eliminate your confusions   good luck

User · Answer

That is called a shebang  it tells the shell what program to interpret the script with  when executed   In your example  the script is to be interpreted and run by the bash shell   Some other example shebangs are    From Wikipedia      bin sh     Execute the file using sh  the Bourne shell  or a compatible shell    bin csh     Execute the file using csh  the C shell  or a compatible shell    usr bin perl -T     Execute using Perl with the option for taint checks    usr bin php     Execute the file using the PHP command line interpreter    usr bin python -O     Execute using Python with optimizations to code    usr bin ruby     Execute using Ruby   and a few additional ones I can think off the top of my head  such as      bin ksh    bin awk    bin expect   In a script with the bash shebang  for example  you would write your code with bash syntax  whereas in a script with expect shebang  you would code it in expect syntax  and so on   Response to updated portion   It depends on what  bin sh actually points to on your system  Often it is just a symlink to  bin bash  Sometimes portable scripts are written with    bin sh just to signify that it s a shell script  but it uses whichever shell is referred to by  bin sh on that particular system  maybe it points to  bin bash   bin ksh or  bin zsh

[bash] Bash Script : what does #!/bin/bash mean?

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