I have made Bash scripts before and they all ran fine without #!/bin/bash at the beginning.
What's the point of putting it in? Would things be any different?
Also, how do you pronounce #? I know that ! is pronounced as "bang."
How is #! pronounced?
It's a convention so the *nix shell knows what kind of interpreter to run.
For example, older flavors of ATT defaulted to sh (the Bourne shell), while older versions of BSD defaulted to csh (the C shell).
Even today (where most systems run bash, the "Bourne Again Shell"), scripts can be in bash, python, perl, ruby, PHP, etc, etc. For example, you might see #!/bin/perl or #!/bin/perl5.
PS: The exclamation mark (!) is affectionately called "bang". The shell comment symbol (#) is sometimes called "hash".
PPS: Remember - under *nix, associating a suffix with a file type is merely a convention, not a "rule". An executable can be a binary program, any one of a million script types and other things as well. Hence the need for #!/bin/bash.
execve(2) syscall; so the shebang is a kernel convention, not a shell one.
To be more precise the shebang #!, when it is the first two bytes of an executable (x mode) file, is interpreted by the execve(2) system call (which execute programs).
But POSIX specification for execve don't mention the shebang.
It must be followed by a file path of an interpreter executable (which BTW could even be relative, but most often is absolute).
A nice trick (or perhaps not so nice one) to find an interpreter (e.g. python) in the user's $PATH is to use the env program (always at /usr/bin/env on all Linux) like e.g.
#!/usr/bin/env python Any ELF executable can be an interpreter. You could even use #!/bin/cat or #!/bin/true if you wanted to! (but that would be often useless)
#!/usr/bin/env hack.
#!/usr/bin/env bash -x. How do i do that ?#!/usr/bin/env bash -xbash is almost always at /bin/bash so your shebang should be #!/bin/bash -xIt's called a shebang. In unix-speak, # is called sharp (like in music) or hash (like hashtags on twitter), and ! is called bang. (You can actually reference your previous shell command with !!, called bang-bang). So when put together, you get haSH-BANG, or shebang.
The part after the #! tells Unix what program to use to run it. If it isn't specified, it will try with bash (or sh, or zsh, or whatever your $SHELL variable is) but if it's there it will use that program. Plus, # is a comment in most languages, so the line gets ignored in the subsequent execution.
execve(2) syscall don't use the $SHELL variable. It is the kernel that is interpreting the shebang.Every distribution has a default shell. Bash is the default on the majority of the systems. If you happen to work on a system that has a different default shell, then the scripts might not work as intended if they are written specific for Bash.
Bash has evolved over the years taking code from ksh and sh.
Adding #!/bin/bash as the first line of your script, tells the OS to invoke the specified shell to execute the commands that follow in the script.
#! is often referred to as a "hash-bang", "she-bang" or "sha-bang".
The shebang is a directive to the loader to use the program which is specified after the #! as the interpreter for the file in question when you try to execute it. So, if you try to run a file called foo.sh which has #!/bin/bash at the top, the actual command that runs is /bin/bash foo.sh. This is a flexible way of using different interpreters for different programs. This is something implemented at the system level and the user level API is the shebang convention.
It's also worth knowing that the shebang is a magic number - a human readable one that identifies the file as a script for the given interpreter.
Your point about it "working" even without the shebang is only because the program in question is a shell script written for the same shell as the one you are using. For example, you could very well write a javascript file and then put a #! /usr/bin/js (or something similar) to have a javascript "Shell script".
The operating system takes default shell to run your shell script. so mentioning shell path at the beginning of script, you are asking the OS to use that particular shell. It is also useful for portability.
It is called a shebang. It consists of a number sign and an exclamation point character (#!), followed by the full path to the interpreter such as /bin/bash. All scripts under UNIX and Linux execute using the interpreter specified on a first line.
Bash standards for “Bourne-Again shell” is just one type of many available shells in Linux.
A shell is a command line interpreter that accepts and runs commands.
Bash is often the default shell in most Linux distributions. This is why bash is synonymous to shell.
The shell scripts often have almost the same syntaxes, but they also differ sometimes. For example, array index starts at 1 in Zsh instead of 0 in bash. A script written for Zsh shell won’t work the same in bash if it has arrays.
To avoid unpleasant surprises, you should tell the interpreter that your shell script is written for bash shell. How do you do that?
simply begin your bash script into #!/bin/bash
Also you will see some other parameters after #!/bin/bash, for example
#!/bin/bash -v -x
read this to get more idea.
https://unix.stackexchange.com/questions/124272/what-do-the-arguments-v-and-x-mean-to-bash .
#!/bin/bash shebang line is all about making sure your script runs smoothly, with the right interpreter, and is easy to use across different environments. It's a small detail that makes a big difference in scripting.
It can be useful to someone that uses a different system that does not have that library readily available. If that is not declared and you have some functions in your script that are not supported by that system, you should declare #/bin/bash. I've ran into this problem before at work and now I just include it as a practice.
./yourscript.extension, for example,./helloworld.pyor./helloworld.sh, it will look for the interpreter at that top line, which would be#!/bin/pythonor!#/bin/bash, whereas when executing the script likepython helloworld.py, the first line will not be observed because it is commented out. So it is a special sequence for the shell/kernel.