Classic Shell Scripting

Unix File Extension Conventions

Some other operating systems have filenames of the form of a base name, a dot, and a one- to three-character file type or file extension. These extensions serve an important purpose: they indicate that the file contents belong to a particular class of data. For example, an extension pas could mean that the file contains Pascal source code, and exe would identify a binary executable program.

There is no guarantee that file contents are reflected in their file extensions, but most users find them a useful custom, and follow convention.

Unix too has a substantial number of common file extensions, but Unix filenames are not forced to have at most one dot. Sometimes, the extensions are merely conventional (e.g., for most scripting languages). However, compilers generally require particular extensions, and use the base name (after stripping the extension) to form the names of other related files. Some of the more common extensions are shown in Table B-1.

Table B-1. Common Unix file extensions

Extension	Contents
1	Digit one. Manual page for section 1 (user commands)
a	Library archive file
awk	awk language source file
bz2	File compressed by bzip2
c	C language source file
cc C cpp cxx	C++ language source file
eps ps	PostScript page-description language source file
f	Fortran 77 language source file
gz	File compressed by gzip
f90	Fortran 90/95/200x language source file
h	C language header file
html htm	HyperText Markup Language file
o	Object ...