A Simple Makefile Tutorial

Makefiles are a simple way to organize code compilation. This tutorial does not even scratch the surface of what is possible using make, but is intended as a starters guide so that you can quickly and easily create your own makefiles for small to medium-sized projects.

A Simple Example

Let's start off with the following three files, hellomake.c, hellofunc.c, and hellomake.h, which would represent a typical main program, some functional code in a separate file, and an include file, respectively.

hellomake.c	hellofunc.c	hellomake.h
#include <hellomake.h> int main() { // call a function in another file myPrintHelloMake(); return(0); }	#include <stdio.h> #include <hellomake.h> void myPrintHelloMake(void) { printf("Hello makefiles!\n"); return; }	/* example include file */ void myPrintHelloMake(void);

Normally, you would compile this collection of code by executing the following command:
gcc -o hellomake hellomake.c hellofunc.c -I.
This compiles the two .c files and names the executable hellomake. The -I. is included so that gcc will look in the current directory (.) for the include file hellomake.h. Without a makefile, the typical approach to the test/modify/debug cycle is to use the up arrow in a terminal to go back to your last compile command so you don't have to type it each time, especially once you've added a few more .c files to the mix.
Unfortunately, this approach to compilation has two downfalls. First, if you lose the compile command or switch computers you have to retype it from scratch, which is inefficient at best. Second, if you are only making changes to one .c file, recompiling all of them every time is also time-consuming and inefficient. So, it's time to see what we can do with a makefile.
The simplest makefile you could create would look something like:
Makefile 1

hellomake: hellomake.c hellofunc.c
     gcc -o hellomake hellomake.c hellofunc.c -I.

If you put this rule into a file called Makefile or makefile and then type make on the command line it will execute the compile command as you have written it in the makefile. Note that make with no arguments executes the first rule in the file. Furthermore, by putting the list of files on which the command depends on the first line after the :, make knows that the rule hellomake needs to be executed if any of those files change. Immediately, you have solved problem #1 and can avoid using the up arrow repeatedly, looking for your last compile command. However, the system is still not being efficient in terms of compiling only the latest changes.
One very important thing to note is that there is a tab before the gcc command in the makefile. There must be a tab at the beginning of any command, and make will not be happy if it's not there.
In order to be a bit more efficient, let's try the following:
Makefile 2

CC=gcc
CFLAGS=-I.

hellomake: hellomake.o hellofunc.o
     $(CC) -o hellomake hellomake.o hellofunc.o

So now we've defined some constants CC and CFLAGS. It turns out these are special constants that communicate to make how we want to compile the files hellomake.c and hellofunc.c. In particular, the macro CC is the C compiler to use, and CFLAGS is the list of flags to pass to the compilation command. By putting the object files--hellomake.o and hellofunc.o--in the dependency list and in the rule, make knows it must first compile the .c versions individually, and then build the executable hellomake.
Using this form of makefile is sufficient for most small scale projects. However, there is one thing missing: dependency on the include files. If you were to make a change to hellomake.h, for example, make would not recompile the .c files, even though they needed to be. In order to fix this, we need to tell make that all .c files depend on certain .h files. We can do this by writing a simple rule and adding it to the makefile.
Makefile 3

CC=gcc
CFLAGS=-I.
DEPS = hellomake.h

%.o: %.c $(DEPS)
 $(CC) -c -o $@ $< $(CFLAGS)

hellomake: hellomake.o hellofunc.o 
 $(CC) -o hellomake hellomake.o hellofunc.o 

This addition first creates the macro DEPS, which is the set of .h files on which the .c files depend. Then we define a rule that applies to all files ending in the .o suffix. The rule says that the .o file depends upon the .c version of the file and the .h files included in the DEPS macro. The rule then says that to generate the .o file, make needs to compile the .c file using the compiler defined in the CC macro. The -c flag says to generate the object file, the -o $@ says to put the output of the compilation in the file named on the left side of the :, the $< is the first item in the dependencies list, and the CFLAGS macro is defined as above.
As a final simplification, let's use the special macros $@ and $^, which are the left and right sides of the :, respectively, to make the overall compilation rule more general. In the example below, all of the include files should be listed as part of the macro DEPS, and all of the object files should be listed as part of the macro OBJ.
Makefile 4

CC=gcc
CFLAGS=-I.
DEPS = hellomake.h
OBJ = hellomake.o hellofunc.o 

%.o: %.c $(DEPS)
 $(CC) -c -o $@ $< $(CFLAGS)

hellomake: $(OBJ)
 $(CC) -o $@ $^ $(CFLAGS)

So what if we want to start putting our .h files in an include directory, our source code in a src directory, and some local libraries in a lib directory? Also, can we somehow hide those annoying .o files that hang around all over the place? The answer, of course, is yes. The following makefile defines paths to the include and lib directories, and places the object files in an obj subdirectory within the src directory. It also has a macro defined for any libraries you want to include, such as the math library -lm. This makefile should be located in the src directory. Note that it also includes a rule for cleaning up your source and object directories if you type make clean. The .PHONY rule keeps make from doing something with a file named clean.
Makefile 5

IDIR =../include
CC=gcc
CFLAGS=-I$(IDIR)

ODIR=obj
LDIR =../lib

LIBS=-lm

_DEPS = hellomake.h
DEPS = $(patsubst %,$(IDIR)/%,$(_DEPS))

_OBJ = hellomake.o hellofunc.o 
OBJ = $(patsubst %,$(ODIR)/%,$(_OBJ))


$(ODIR)/%.o: %.c $(DEPS)
 $(CC) -c -o $@ $< $(CFLAGS)

hellomake: $(OBJ)
 $(CC) -o $@ $^ $(CFLAGS) $(LIBS)

.PHONY: clean

clean:
 rm -f $(ODIR)/*.o *~ core $(INCDIR)/*~ 

So now you have a perfectly good makefile that you can modify to manage small and medium-sized software projects. You can add multiple rules to a makefile; you can even create rules that call other rules. For more information on makefiles and the make function, check out the GNU Make Manual, which will tell you more than you ever wanted to know (really).

Linux diff command

Updated: 01/24/2018 by Computer Hope

• About diff
• diff syntax
• diff examples
• Related commands
• Linux and Unix commands help

About diff

diff analyzes two files and prints the lines that are different. Essentially, it outputs a set of instructions for how to change one file to make it identical to the second file.

It does not actually change the files; however, it can optionally generate a script (with the -e option) for the program ed (or ex which can be used to apply the changes.

How diff Works

Let's say we have two files, file1.txt and file2.txt.

If file1.txt contains the following four lines of text:

I need to buy apples.
I need to run the laundry.
I need to wash the dog.
I need to get the car detailed.

...and file2.txt contains these four lines:

I need to buy apples.
I need to do the laundry.
I need to wash the car.
I need to get the dog detailed.

...then we can use diff to automatically display for us which lines differ between the two files with this command:

diff file1.txt file2.txt

...and the output will be:

2,4c2,4
< I need to run the laundry.
< I need to wash the dog.
< I need to get the car detailed.
---
> I need to do the laundry.
> I need to wash the car.
> I need to get the dog detailed.

Let's take a look at what this output means. The important thing to remember is that when diff is describing these differences to you, it's doing so in a prescriptive context: it's telling you how to change the first file to make it match the second file.

The first line of the diff output will contain:

• line numbers corresponding to the first file,
• a letter (a for add, c for change, or d for delete), and
• line numbers corresponding to the second file.

In our output above, "2,4c2,4" means: "Lines 2 through 4 in the first file need to be changed to match lines 2 through 4 in the second file." It then tells us what those lines are in each file:

• Lines preceded by a < are lines from the first file;
• lines preceded by > are lines from the second file.

The three dashes ("---") merely separate the lines of file 1 and file 2.

Let's look at another example. Let's say our two files look like this:

file1.txt:

I need to go to the store.
I need to buy some apples.
When I get home, I'll wash the dog.

file2.txt:

I need to go to the store.
I need to buy some apples.
Oh yeah, I also need to buy grated cheese.
When I get home, I'll wash the dog.

diff file1.txt file2.txt

Output:

2a3
> Oh yeah, I also need to buy grated cheese.

Here, the output is telling us "After line 2 in the first file, a line needs to be added: line 3 from the second file." It then shows us what that line is.

Now let's see what it looks like when diff tells us we need to delete a line.

file1:

I need to go to the store.
I need to buy some apples.
When I get home, I'll wash the dog.
I promise.

file2:

I need to go to the store.
I need to buy some apples.
When I get home, I'll wash the dog.

Our command:

diff file1.txt file2.txt

The output:

4d3
< I promise.

Here, the output is telling us "You need to delete line 4 in the first file so that both files sync up at line 3." It then shows us the contents of the line that needs to be deleted.

Viewing diff Output In Context

The examples above show the default output of diff. It's intended to be read by a computer, not a human, so for human purposes, sometimes it helps to see the context of the changes.

GNU diff, which is the version most linux users will be using, offers two different ways to do this: "context mode" and "unified mode".

To view differences in context mode, use the -c option. For instance, let's say file1.txt and file2.txt contain the following:

file1.txt:

apples
oranges
kiwis
carrots

file2.txt:

apples
kiwis
carrots
grapefruits

Let's look at the contextual output for the diff of these two files. Our command is:

diff -c file1.txt file2.txt

And our output looks like this:

*** file1.txt   2014-08-21 17:58:29.764656635 -0400
--- file2.txt   2014-08-21 17:58:50.768989841 -0400
***************
*** 1,4 ****
  apples
- oranges
  kiwis
  carrots
--- 1,4 ----
  apples
  kiwis
  carrots
+ grapefruits

The first two lines of this output show us information about our "from" file (file 1) and our "to" file (file 2). It lists the file name, modification date, and modification time of each of our files, one per line. The "from" file is indicated by "***", and the "to" file is indicated by "---".

The line "***************" is just a separator.

The next line has three asterisks ("***") followed by a line range from the first file (in this case lines 1 through 4, separated by a comma). Then four asterisks ("****").

Then it shows us the contents of those lines. If the line is unchanged, it's prefixed by two spaces. If the line is changed, however, it's prefixed by an indicative character and a space. The character meanings are as follows:

character	meaning
!	Indicates that this line is part of a group of one or more lines that needs to change. There is a corresponding group of lines prefixed with "!" in the other file's context as well.
+	Indicates a line in the second file that needs to be added to the first file.
-	Indicates a line in the first file that needs to be deleted.

After the lines from the first file, there are three dashes ("---"), then a line range, then four dashes ("----"). This indicates the line range in the second file that will sync up with our changes in the first file.

If there is more than one section that needs to change, diff will show these sections one after the other. Lines from the first file will still be indicated with "***", and lines from the second file with "---".

Unified Mode

Unified mode (the -u option) is similar to context mode, but it doesn't display any redundant information. Here's an example, using the same input files as our last example:

file1.txt:

apples
oranges
kiwis
carrots

file2.txt:

apples
kiwis
carrots
grapefruits

Our command:

diff -u file1.txt file2.txt

The output:

--- file1.txt   2014-08-21 17:58:29.764656635 -0400
+++ file2.txt   2014-08-21 17:58:50.768989841 -0400
@@ -1,4 +1,4 @@
 apples
-oranges
 kiwis
 carrots
+grapefruits

The output is similar to above, but as you can see, the differences are "unified" into one set.

Finding Differences In Directory Contents

diff can also compare directories by providing directory names instead of file names. See the Examples section.

Using diff To Create An Editing Script

The -e option tells diff to output a script, which can be used by the editing programs ed or ex, that contains a sequence of commands. The commands are a combination of c (change), a (add), and d (delete) which, when executed by the editor, will modify the contents of file1 (the first file specified on the diff command line) so that it matches the contents of file2 (the second file specified).

Let's say we have two files with the following contents:

file1.txt:

Once upon a time, there was a girl named Persephone.
She had black hair.
She loved her mother more than anything.
She liked to sit outside in the sunshine with her cat, Daisy.
She dreamed of being a painter when she grew up.

file2.txt

Once upon a time, there was a girl named Persephone.
She had red hair.
She loved chocolate chip cookies more than anything.
She liked to sit outside in the sunshine with her cat, Daisy.
She would look up into the clouds and dream of being a world-famous baker.

We can run the following command to analyze the two files with diff and produce a script to create a file identical to file2.txt from the contents of file1.txt:

diff -e file1.txt file2.txt

...and the output will look like this:

5c
She would look up into the clouds and dream of being a world-famous baker.
.
2,3c
She had red hair.
She loved chocolate chip cookies more than anything.
.

Notice that the changes are listed in reverse order: the changes closer to the end of the file are listed first, and changes closer to the beginning of the file are listed last. This order is to preserve line numbering; if we made the changes at the beginning of the file first, that might change the line numbers later in the file. So the script starts at the end, and works backwards.

Here, the script is telling the editing program: "change line 5 to (the following line), and change lines 2 through 3 to (the following two lines)."

Next, we should save the script to a file. We can redirect the diff output to a file using the > operator, like this:

diff -e file1.txt file2.txt > my-ed-script.txt

This command will not display anything on the screen (unless there is an error); instead, the output is redirected to the file my-ed-script.txt. If my-ed-script.txt doesn't exist, it will be created; if it exists already, it will be overwritten.

If we now check the contents of my-ed-script.txt with the cat command...

cat my-ed-script.txt

...we will see the same script we saw displayed above.

There's still one thing missing, though: we need the script to tell ed to actually write the file. All that's missing from the script is the w command, which will write the changes. We can add this to our script by echoing the letter "w" and using the >> operator to add it to our file. (The >> operator is similar to the > operator. It redirects output to a file, but instead of overwriting the destination file, it appends to the end of the file.) The command looks like this:

echo "w" >> my-ed-script.txt

Now, we can check to see that our script has changed by running the cat command again:

cat my-ed-script.txt

5c
She would look up into the clouds and dream of being a world-famous baker.
.
2,3c
She had red hair.
She loved chocolate chip cookies more than anything.
.
w

Now our script, when issued to ed, will make the changes and write the changes to disk.

So how do we get ed to do this?

We can issue this script to ed with the following command, telling it to overwrite our original file. The dash ("-") tells ed to read from the standard input, and the < operator directs our script to that input. In essence, the system enters whatever is in our script as input to the editing program. The command looks like this:

ed - file1.txt < my-ed-script.txt

This command displays nothing, but if we look at the contents of our original file...

cat file1.txt

Once upon a time, there was a girl named Persephone.
She had red hair.
She loved chocolate chip cookies more than anything.
She liked to sit outside in the sunshine with her cat, Daisy.
She would look up into the clouds and dream of being a world-famous baker.

...we can see that file1.txt now matches file2.txt exactly.

Warning! In this example, ed overwrote the contents of our original file, file1.txt. After running the script, the original text of file1.txt disappears, so make sure you understand what you're doing before running these commands!

Commonly-Used diff Options

Here are some useful diff options to take note of:

-b	Ignore any changes which only change the amount of whitespace (such as spaces or tabs).
-w	Ignore whitespace entirely.
-B	Ignore blank lines when calculating differences.
-y	Display output in two columns.

These are only some of the most commonly-used diff options. What follows is a complete list of diff options and their function.

diff syntax

diff [OPTION]... FILES

Options

--normal	Output a "normal" diff, which is the default.
-q, --brief	Produce output only when files differ. If there are no differences, output nothing.
-s, --report-identical-files	Report when two files are the same.
-c, -C NUM, --context[=NUM]	Provide NUM (default 3) lines of context.
-u, -U NUM, --unified[=NUM]	Provide NUM (default 3) lines of unified context.
-e, --ed	Output an ed script.
-n, --rcs	Output an RCS-format diff.
-y, --side by side	Format output in two columns.
-W, --width=NUM	Output at most NUM (default 130) print columns.
--left-column	Output only the left column of common lines.
--suppress-common-lines	Do not output lines common between the two files.
-p, --show-c-function	For files that contain C code, also show each C function change.
-F, --show-function-line=RE	Show the most recent line matching regular expression RE.
--label LABEL	When displaying output, use the label LABEL instead of the file name. This option can be issued more than once for multiple labels.
-t, --expand-tabs	Expand tabs to spaces in output.
-T, --initial-tab	Make tabs line up by prepending a tab if necessary.
--tabsize=NUM	Define a tab stop as NUM (default 8) columns.
--suppress-blank-empty	Suppress spaces or tabs before empty output lines.
-l, --paginate	Pass output through pr to paginate.
-r, --recursive	Recursively compare any subdirectories found.
-N, --new-file	If a specified file does not exist, perform the diff as if it is an empty file.
--unidirectional-new-file	Same as -n, but only applies to the first file.
--ignore-file-name-case	Ignore case when comparing file names.
--no-ignore-file-name-case	Consider case when comparing file names.
-x, --exclude=PAT	Exclude files that match file name pattern PAT.
-X, --exclude-from=FILE	Exclude files that match any file name pattern in file FILE.
-S, --starting-file=FILE	Start with file FILE when comparing directories.
--from-file=FILE1	Compare FILE1 to all operands; FILE1 can be a directory.
--to-file=FILE2	Compare all operands to FILE2; FILE2 can be a directory.
-i, --ignore-case	Ignore case differences in file contents.
-E, --ignore-tab-expansion	Ignore changes due to tab expansion.
-b, --ignore-space-change	Ignore changes in the amount of white space.
-w, --ignore-all-space	Ignore all white space.
-B, --ignore-blank-lines	Ignore changes whose lines are all blank.
-I, --ignore-matching-lines=RE	Ignore changes whose lines all match regular expression RE.
-a, --text	Treat all files as text.
--strip-trailing-cr	Strip trailing carriage return on input.
-D, --ifdef=NAME	Output merged file with "#ifdef NAME" diffs.
--GTYPE-group-format=GFMT	Format GTYPE input groups with GFMT.
--line-format=LFMT	Format all input lines with LFMT.
--LTYPE-line-format=LFMT	Format LTYPE input lines with LFMT. These format options provide fine-grained control over the output of diff, generalizing -D/--ifdef. LTYPE is old, new, or unchanged. GTYPE can be any of the LTYPE values, or the value changed. GFMT (but not LFMT) may contain: %< lines from FILE1 %> lines from FILE2 %= lines common to FILE1 and FILE2.
%[-][WIDTH][.[PREC]]{doxX}LETTER	printf-style spec for LETTER

LETTERs are as follows for new group, lower case for old group:

F	First line number.
L	Last line number,
N	Number of lines = L - F + 1.
E	F - 1
M	L + 1
%(A=B?T:E)	If A equals B then T else E.

LFMT (only) may contain:

%L	Contents of line.
%l	Contents of line, excluding any trailing newline.
%[-][WIDTH][.[PREC]]{doxX}n	printf-style spec for input line number.

Both GFMT and LFMT may contain:

%%	A literal %.
%c'C'	The single character C.
%c'\OOO'	The character with octal code OOO.
C	The character C (other characters represent themselves).
-d, --minimal	Try hard to find a smaller set of changes.
--horizon-lines=NUM	Keep NUM lines of the common prefix and suffix.
--speed-large-files	Assume large files and many scattered small changes.
--help	Display a help message and exit.
-v, --version	Output version information and exit.

FILES takes the form "FILE1 FILE2" or "DIR1 DIR2" or "DIR FILE..." or "FILE... DIR".

If the --from-file or --to-file options are given, there are no restrictions on FILE(s). If a FILE is a dash ("-"), diff reads from standard input.

Exit status is either 0 if inputs are the same, 1 if different, or 2 if diff encounters any trouble.

diff examples

Here's an example of using diff to examine the differences between two files side by side using the -y option, given the following input files:

file1.txt:

apples
oranges
kiwis
carrots

file2.txt:

apples
kiwis
carrots
grapefruits

diff -y file1.txt file2.txt

Output:

apples            apples
oranges         <
kiwis             kiwis
carrots           carrots
                > grapefruits

And as promised, here is an example of using diff to compare two directories:

diff dir1 dir2

Output:

Only in dir1: tab2.gif
Only in dir1: tab3.gif
Only in dir1: tab4.gif
Only in dir1: tape.htm
Only in dir1: tbernoul.htm
Only in dir1: tconner.htm
Only in dir1: tempbus.psd

chkconfig

The chkconfig command can also be used to activate and deactivate services. The chkconfig --listcommand displays a list of system services and whether they are started (on) or stopped (off) in runlevels 0-6. At the end of the list is a section for the services managed by xinetd.

If the chkconfig --list command is used to query a service managed by xinetd, it displays whether the xinetd service is enabled (on) or disabled (off). For example, the command chkconfig --list rsync returns the following output:

rsync          on

As shown, rsync is enabled as an xinetd service. If xinetd is running, rsync is enabled.

If you use chkconfig --list to query a service in /etc/rc.d, that service's settings for each runlevel are displayed. For example, the command chkconfig --list httpd returns the following output:

httpd         0:off   1:off   2:on    3:on    4:on    5:on    6:off

chkconfig can also be used to configure a service to be started (or not) in a specific runlevel. For example, to turn nscd off in runlevels 3, 4, and 5, use the following command:

chkconfig --level 345 nscd off

How to monitor only the last n lines of a log file?

It might suffice to use watch:

$ watch tail -n 15 mylogfile.txt

How to get the current date and time in the terminal

The command is date
To customise the output there are a myriad of options available, see date --help for a list.
For example, date '+%A %W %Y %X' gives Tuesday 34 2013 08:04:22 which is the name of the day of the week, the week number, the year and the time.

Octave for GNU/Linux

The recommended way for installing Octave and Octave-Forge packages on GNU/Linux systems is via each distribution package installation system.
More detailed instructions follow.

Contents

• 1 Debian and Debian-based (such as Ubuntu)
• 2 Fedora
• 3 Gentoo
• 4 Red Hat Enterprise/CentOS
• 5 SUSE Linux and openSUSE
• 6 Arch Linux

Debian and Debian-based (such as Ubuntu)

Main article: Octave for Debian systems

Simply install Octave from your distribution repository:

apt-get install octave

For old versions of Ubuntu that only supply old versions of Octave, consider using Octave's PPA. For more details, see the Debian specific instructions page.
There are also Debian packages for each of the Octave-Forge packages, usually named octave<pkgname>, e.g, octave-image and octave-statistics for the image processing and statistics package respectively. A complete list of them can be found with the command:

aptitude search ?description\(octave-forge\)

Fedora

Main article: Octave for Red Hat Linux systems

The packages can be installed using the dnf command, they are:

• octave
• octave-devel

octave-devel contains the octave headers and mkoctfile script and is really only needed by users who are developing code that is to be dynamically linked to octave. octave can be installed with the command:

   # dnf install octave

Gentoo

Octave is available through Gentoo's package management system, Portage:

   # emerge --sync

Add USE flag 'curl' into your /etc/portage/package.use file to enable remote Octave-Forge packages fetching

sci-mathematics/octave curl

and emerge Octave

   # emerge octave

Since Octave ver. > 3.4.0 is able to fetch Octave-Forge packages from remote repository, packages octave-forge or g-octave are no more needed.
Before installing any Octave-Forge package, in Octave command prompt you must type

pkg -forge list

and then install your favourite packages. Typically, you have to start with

pkg install -forge general

Red Hat Enterprise/CentOS

Main article: Octave for Red Hat Linux systems

Octave is available for Red Hat Enterprise Linux distributions through the EPEL repository. This section applies to CentOS, Scientific Linux, and other Red Hat Enterprise rebuild distributions as well.
Method 1 - the quick way:

   yum install epel-release
   yum install octave

Method 2 - if the above does not work:
First, follow these instructions to set up your system to install packages from EPEL. For example,

   # wget http://url/to/latest/epel-release-6-7.noarch.rpm
   # yum localinstall epel-release-6-7.noarch.rpm

Once the EPEL repository has been enabled, you can follow the rest of the instructions for Fedora to install Octave using yum.
Note that EPEL intentionally does not follow new releases as closely as other distributions. Consequently, the version of Octave provided by EPEL may be several months or years out of date. There are plans for the Octave maintainers to provide support and binary RPMs for enterprise GNU/Linux distributions; contact the maintainers mailing list for more information.

SUSE Linux and openSUSE

Main article: Octave for openSUSE

Binary packages for Octave are provided by all versions of openSUSE. It can be installed by command:

zypper in octave

Latest stable version of Octave and Octave-Forge are available on Science repository. For details see openSUSE specific wiki page.

Arch Linux

Main article: Octave for Arch Linux

Updated Octave's version is in the extra repository. It can be installed by typing:

   # pacman -S octave