![\"bash](\"https:\/\/linoxide.com\/wp-content\/uploads\/2018\/09\/bash-shebang-linux-functions.png\")
<\/p>\n<\/p>\n
The #! characters form a magic number. We embed these magic number in any scripts under UNIX \/ Linux operating systems to tell the kernel what interpreter to execute, to read our script. Like Linux shell, Python, Perl and R interpreters. You might have noticed all Linux shell and Perl \/ python script starts with the below line:<\/p>\n
#!\/bin\/bash<\/p>\n
OR<\/p>\n
#!\/usr\/bin\/env python<\/p>\n
OR<\/p>\n
#!\/usr\/bin\/env perl<\/p>\n
OR<\/p>\n
#!\/usr\/bin\/env Rscript<\/p>\n
Now we will write a program file for Python language. we can execute this program by calling the interpreter directly without adding shebang line like below.<\/p>\n
import sys
\n
\ndef greeting(name):
\n sys.stdout.write(“Hello” + name + “n”)
\n
\nname = “Omar”
\ngreeting(name)
<\/p>\n
For executing the code, we will mention python before name of the file.<\/p>\n
python python_script.py
\nOutput
\n Hello Omar
<\/p>\n
Also we will write a program file for R language. we can execute this program by calling the interpreter directly without adding shebang line like below.<\/p>\n
print(“hello world”) <\/p>\n
For executing the code, we will mention Rscript before name of the file.<\/p>\n
Rscript r_script.R
\nOutput
\n “hello world”
<\/p>\n
to make executable file we should add shebang line #!\/usr\/bin\/python to the top of script and changing the mode of the file to be executable.<\/p>\n
#!\/usr\/bin\/python
\nimport sys
\n
\ndef greeting(name):
\n sys.stdout.write(“Hello” + name + “n”)
\n
\nname = “Omar”
\ngreeting(name)
<\/p>\n
To make the file is executable, type the command below.<\/p>\n
chmod +x python_script.py<\/p>\n
Now we can just run the file and it will be interpreted by python.<\/p>\n
.\/python_script.py
\nOutput
\n Hello Omar
<\/p>\n
The path \/usr\/bin\/python will probably work for most default systems but might not work on things like a large computer cluster. So we will use the program env to get the right interperter.<\/p>\n
#!\/usr\/bin\/env python
\nimport sys
\n
\ndef greeting(name):
\n sys.stdout.write(“Hello” + name + “n”)
\n
\nname = “Omar”
\ngreeting(name)
<\/p>\n
We can do the same for any program like Rscript as well.<\/p>\n
#!\/usr\/bin\/env Rscript
\n print(“hello world”)
<\/p>\n