What does the line bin sh mean in a UNIX shell script

Question

I was going through some shell script tutorials and found the following sample program      bin sh clear echo  HELLO WORLD    Can anyone please tell me what the significance of the comment    bin sh at the start is

User · Answer

The first line tells the shell that if you execute the script directly (./run.sh; as opposed to /bin/sh run.sh), it should use that program (/bin/sh in this case) to interpret it.

You can also use it to pass arguments, commonly -e (exit on error), or use other programs (/bin/awk, /usr/bin/perl, etc).

User · Answer

It s called a shebang  and tells the parent shell which interpreter should be used to execute the script     bin sh  lt --------- bourne shell compatible script    usr bin perl   lt -- perl script    usr bin php   lt --- php script    bin false  lt ------ do-nothing script  because false returns immediately anyways   Most scripting languages tend to interpret a line starting with   as comment and will ignore the following   usr bin whatever portion  which might otherwise cause a syntax error in the interpreted language

User · Answer

When you try to execute a program in unix  one with the executable bit set   the operating system will look at the first few bytes of the file   These form the so-called  magic number   which can be used to decide the format of the program and how to execute it      corresponds to the magic number 0x2321  look it up in an ascii table    When the system sees that the magic number  it knows that it is dealing with a text script and reads until the next  n  there is a limit  but it escapes me atm   Having identified the interpreter  the first argument after the shebang  it will call the interpreter   Other files also have magic numbers   Try looking at a bitmap   BMP  file via less and you will see the first two characters are BM   This magic number denotes that the file is indeed a bitmap

User · Answer

If the file that this script lives in is executable  the hash-bang      tells the operating system what interpreter to use to run the script  In this case it s  bin sh  for example    There s a Wikipedia article about it for more information

User · Answer

bin sh or    bin bash has to be first line of the script because if you don t use it on the first line then the system will treat all the commands in that script as different commands  If the first line is    bin sh then it will consider all commands as a one script and it will show the that this file is running in ps command and not the commands inside the file     echo sh  ps -ef  grep echo trainee   3036  2717  0 16 24 pts 0    00 00 00  bin sh   echo sh root      3042  2912  0 16 24 pts 1    00 00 00 grep --color auto echo

[shell] What does the line "#!/bin/sh" mean in a UNIX shell script?

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