Interpreter directive

{{short description|Computer language construct to control an interpreter}}

{{Confusing|date=February 2016}}

{{Duplication|date=March 2023|dupe=Directive (programming)|dupe2=Shebang (Unix)}}

An interpreter directive is a computer language construct, that on some systems is better described as an aspect of the system's executable file format, that is used to control which interpreter parses and interprets the instructions in a computer program.{{cite book|last1= Weik |first1= Martin H. |title= Computer Science and Communications Dictionary |url= https://books.google.com/books?id=gbP1bLDPKlYC&pg=PA829 |volume= 1 |year= 2000 |publisher= Springer |isbn= 978-0-7923-8425-0 |page= 829 }}

In Unix, Linux and other Unix-like operating systems, the first two bytes in a file can be the characters "#!", which constitute a magic number (hexadecimal 23 and 21, the ASCII values of "#" and "!") often referred to as shebang, prefix the first line in a script, with the remainder of the line being a command usually limited to a max of 14 (when introduced) up to usually about 80 characters in 2016{{Citation needed|date = May 2016}}. If the file system permissions on the script (a file) include an execute permission bit for the user invoking it by its filename (often found through the command search path), it is used to tell the operating system what interpreter (usually a program that implements a scripting language) to use to execute the script's contents, which may be batch commands or might be intended for interactive use. An example would be #!/bin/bash, meaning run this script with the bash shell found in the /bin directory.{{cite web|title=Advanced Bash Scripting Guide|url=http://tldp.org/LDP/abs/html/sha-bang.html|access-date=2012-01-19}}{{cite book

|last=Cooper

|first=Mendel

|title=Advanced Bash Scripting Guide 5.3 Volume 1

|publisher=lulu.com

|date=November 5, 2010

|isbn=978-1-4357-5218-4

|page=5

|url=https://books.google.com/books?id=WPXkgFRd4OEC&q=sha-bang&pg=PA5

}}{{cite book

|last=MacDonald

|first=Matthew

|title=HTML5: The Missing Manual

|publisher=O'Reilly Media

|location=Sebastopol, California

|year=2011

|isbn=978-1-4493-0239-9

|page=373

|url=https://books.google.com/books?id=SR7HXy2XvBEC&pg=PA373

}}{{cite book

|last=Lutz

|first=Mark

|title=Learning Python

|edition=4th

|publisher=O'Reilly Media

|date=September 2009

|isbn=978-0-596-15806-4

|page=48

|url=https://books.google.com/books?id=1HxWGezDZcgC&pg=PA48

}}{{cite book

|last=Lie Hetland

|first=Magnus

|title=Beginning Python: From Novice to Professional

|publisher=Apress

|date=October 4, 2005

|isbn=978-1-59059-519-0

|page=21

|url=https://books.google.com/books?id=S0l1YFpRFVAC&q=pound+bang&pg=PA21

}}{{cite book

|last=Schitka

|first=John

|title=Linux+ Guide to Linux Certification

|publisher=Course Technology

|date=December 24, 2002

|isbn=978-0-619-13004-6

|page=353

|url=https://books.google.com/books?id=l7JhL9rJLEgC&q=hashpling&pg=PA353

}}

Other systems or files may use some other magic number as the interpreter directives.{{Citation needed|date=March 2023}}