Page 200 - DCAP602_NETWORK_OPERATING_SYSTEMS_I

Network Operating Systems-I

notes

Note The same scheme of creating backup files is used by the Emacs editor.

sedutility

The sed utility is a stream editor that can be used for different file editing purposes when used
as a filter. The most common task for software development purposes is the use of sed to search
and replace text in source code files.
This utility reads one or more text files, makes editing changes according to a script of editing
commands, and writes the results to standard output. The script is obtained from either the script
operand string or a combination of the option-arguments from the -e script and -f script_file
options.
The sed utility supports the XBD specification, Utility Syntax Guidelines, except that the order of
presentation of the -e and -f options is significant.

The following options are supported:
-e script: Add the editing commands specified by the script option-argument to the end of the
script of editing commands. The script option-argument has the same properties as the script
operand, described in the OPERANDS section.
-f script_file: Add the editing commands in the file script_file to the end of the script.
-n: Suppress the default output (in which each line, after it is examined for editing, is written to
standard output). Only lines explicitly selected for output will be written.

Multiple -e and -f options may be specified. All commands are added to the script in the order
specified, regardless of their origin.
The following operands are supported:

file: A pathname of a file whose contents will be read and edited. If multiple file operands are
specified, the named files will be read in the order specified and the concatenation will be edited.
If no file operands are specified, the standard input will be used.
script: A string to be used as the script of editing commands. The application must not present a
script that violates the restrictions of a text file except that the final character need not be a new-
line character.
stdin: The standard input will be used only if no file operands are specified.
input files: The input files must be text files. The script_files named by the -f option will consist
of editing commands, one per line.
Diff utility: The diff utility is another useful tool that developers may need. It is used to find out
the differences between two files. If you are using CVS, differences between different versions
of a file in the CVS repository can be found using the cvs (cvs diff) command as well. However,
if you want to find out the difference between two files that are not in the CVS repository, the
diff utility may be quite handy. One common use may be to find out the difference between the
working copy and the backup copy of a source code file. This will enable you to find out what
changes have been made in the working copy of the file. The output of the diff utility follows
similar rules to those used in the CVS diff command. It displays the differences between two files,
or each corresponding file in two directories.

Each set of differences is called a “diff” or “patch”. For files that are identical, diff normally
produces no output; for binary (non-text) files, diff normally reports only that they are different.
Syntax is diff [options] from-file to-file

194 LoveLy professionaL university