Set number in linux

Linux/Unix: Cat Command Display Line Numbers

H ow do I use the cat command to display the line numbers for a file called myapp.c under Linux or Unix like operating systems?

You can use the cat command concatenate files and show on the screen under Linux or Unix like operating systems.

Tutorial details
Difficulty level	Easy
Root privileges	No
Requirements	cat command on Linux or Unix
Est. reading time	2 mintues

The cat command also number all output lines starting with number one with the following syntax:

Syntax For Cat Command To Display Line Numbers

The syntax is as follows:
cat -n fileNameHere
cat —number foo.c
We can use the more command/less command as filter when text can not be fitted on the screen:
cat —number foo.c | more
cat —number foo.c | less

Displaying line number using cat command

The -b / —number-nonblank option number all nonempty output lines, starting with one and the syntax is:
cat -b fileNameHere
OR
cat —number—nonblank filename

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Removing empty output while showing line numbers

Finally, you suppress or remove repeated empty output lines with the -s / —squeeze-blank option:
cat -s -n fileNameHere
cat -s -n /etc/resolv.conf
Sample outputs:

OR (GNU only syntax)
cat —squeeze-blank -n filename

Say hello to nl command

Use the nl command number lines of files under Linux or Unix oses. The syntax is:

Examples

Create a text file called hello.c as follows:

Use the cat or nl command to display line numbers:

Fig.01: Displaying line numbers for hello.c using the cat and nl command.

A note about sed

To just print 3rd line use the sed command:
sed -n 3p /etc/resolv.conf
To just print 3rd and 5th line use the sed command:
sed -n -e 3p -e 5p /etc/resolv.conf
To see specific range, say show lines between 3 to 5, run:
sed -n 3,5p /etc/resolv.conf

Summing up

You learned various commands that can display line numbers on Linux or Unix-like systems. See the following man page:
man cat
man nl
man sed

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Comments on this entry are closed.

Hi Thanks for sharing … Its of great help …
And I m a great fan of your … because I found 90% of what i think on cyberciti.

Just a little correction here in this post ..
“cat –number–nonblank filename ”
is giving error
cat: unrecognized option ‘–number–nonblank’
Try ‘cat –help’ for more information.

Just make it
“cat –number-nonblank filename”
a single hyphen – after number

But we had a trouble. “cat” command does not stop display when the text is full screen.
So, we have any other option to resolve this in-convenience.

The standard output could instead be redirected using a pipe (represented by a vertical bar) to a filter (i.e., a program that transforms data in some meaningful way) for further processing. For example, if the file is too large for all of the text to fit on the monitor screen simultaneously, as is frequently the case, the text will scroll down the screen at high speed and be very difficult to read. This problem is easily solved by piping the output to the filter less, i.e.,

cat file1 | less

This allows the user to advance the contents of the file one screenful at a time by pressing the space bar and to move backwards by pressing the b key. The user can exit from less by pressing the q key.

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Linux set and unset

On Unix-like operating systems, the set command is a built-in function of the Bourne shell (sh), C shell (csh), and Korn shell (ksh), which is used to define and determine the values of the system environment.

Syntax

Bourne shell (sh):

Options: Bourne Shell (sh)

In sh, the set built-in command has the following options:

—	An option of a double-dash («—«) signifies the end of an option list. This option is primarily useful when values listed after the options start with a dash themselves.
-a	Mark variables that are modified or created for «export»; environment variables set in this way will be passed on to the environments of any subsequent commands.
-e	Exit immediately if a command exits with a non-zero exit status.
-f	Disable file name generation (globbing).
-h	Locate and remember function commands as functions are defined (function commands are normally located when the function is executed).
-k	All keyword arguments are placed in the environment for a command, not only those that precede the command name.
-n	Read commands but do not execute them.
-t	Exit after reading and executing one command.
-u	Treat unset variables as an error when substituting.
-v	Print shell input lines as they are read.
-x	Print commands and their arguments as they are executed.

Using + rather than — causes these flags to be turned off. These flags can also be used upon invocation of the shell itself. The current set of flags are found in the variable $-. The remaining arguments are positional parameters and are assigned, in order, to $1, $2, etc. If no arguments are given the values of all names are printed.

For each name, the unset command removes the corresponding variable or function value. The special variables PATH, PS1, PS2, MAILCHECK, and IF cannot be unset.

With the export built-in command, the given names are marked for automatic export to the environment of subsequently executed commands. If no arguments are given, variable names that are marked for export during the current shell’s execution are listed. Function names are not exported.

Options: C Shell (csh)

In csh, If no arguments are specified, set displays the values of all shell variables. Multiword values are displayed as a parenthesized list. With the var argument alone, set assigns an empty (null) value to the variable var. With arguments of the form var = value, set assigns value to var, where value is one of:

word	A single word (or quoted string).
(wordlist)	A space-separated list of words enclosed in parentheses.

Values are command and file name expanded before being assigned. The form set var[n]=word replaces the n‘th word in a multiword value with word.

unset removes variables whose names match (using file name substitution) pattern. All variables are removed by «unset *«; this is a very bad idea if you don’t know what you’re doing, though.

Options: K Shell (ksh)

In ksh, the set command takes the following options:

-A	Array assignment. Unset the variable name and assign values sequentially from the list arg. If +A is used, the variable name is not unset first.
-a	All subsequent variables that are defined are automatically exported.
-e	If a command has a non-zero exit status, execute the ERR trap (if set), and exit. This mode is disabled while reading profiles.
-f	Disables file name generation (globbing).
-h	Each command becomes a tracked alias when first encountered.
-k	All variable assignment arguments are placed in the environment for a command, not only those preceding the command name.
-m	Background jobs run in a separate process group and a line prints upon completion. The exit status of background jobs is reported in a completion message. On systems with job control, this flag is turned on automatically for interactive shells.
-n	Read commands and check them for syntax errors, but do not execute them. Ignored for interactive shells.
-o option	The option argument can be one of the following: allexport Same as -a. errexit Same as -e. bgnice All background jobs are run at a lower priority, which is the default mode. emacs Puts you in an emacs-style in-line editor for command entry. emacs Puts you in a gmacs-style in-line editor for command entry. ignoreeof The shell will not exit on end-of-file. The command exit must be used. keyword Same as -k. markdirs All directory names resulting from file name generation have a trailing «/» appended. monitor Same as -m. noclobber Prevents redirection «>» from truncating existing files. Require «>|» to truncate a file when turned on. noexec Same as -n. noglob Same as -f. nolog Do not save function definitions in history file. nounset Same as -u. privileged Same as -p. verbose Same as -v. trackall Same as -h. vi Puts you in insert mode of a vi-style in-line editor until you hit escape. This option argument puts you in control mode. A return sends the line. viraw Each character is processed as it is typed in vi mode. xtrace Same as -x. If no option name is supplied then the current option settings are printed.
-p	Disables processing of the $HOME/.profile file and uses the file /etc/suid_profile instead of the ENV file. This mode is on whenever the effective uid (user ID) is not equal to the real uid, or when the effective gid (group ID) is not equal to the real gid. Turning this off causes the effective uid and gid to be set to the real uid and gid.
-s	Sort the positional parameters lexicographically.
-t	Exit after reading and executing one command.
-u	Treat unset parameters as an error when substituting.
-v	Print shell input lines as they are read.
-x	Print commands and their arguments as they are executed.
—	Turns off -x and -v flags and stops examining arguments for flags.
—	Do not change any of the flags; useful in setting $1 to a value beginning with —. If no arguments follow this flag, then the positional parameters are unset.

Using + rather than — causes these flags to be turned off. These flags can also be used upon invocation of the shell. The current set of flags are found in $-. Unless -A is specified, the remaining arguments are positional parameters and are assigned, in order, to «$1 $2 . «. If no arguments are given, then the names and values of all variables are printed on the standard output.

The variables given by the list of names are automatically unassigned: their values and attributes are erased. Readonly variables cannot be unset. If the -f flag is set, then the names refer to function names. Unsetting ERRNO, LINENO, MAILCHECK, OPTARG, OPTIND, RANDOM, SECONDS, TMOUT, and _ removes their special meaning even if they are subsequently assigned.

When using unset, the variables given by the list of names are similarly unassigned: their values and attributes are erased. Readonly variables cannot be unset. If the -f, flag is set, then the names refer to function names. Unsetting ERRNO, LINENO, MAILCHECK, OPTARG, OPTIND, RANDOM, SECONDS, TMOUT, and _ removes their special meaning even if they are subsequently assigned.

With the export built-in command, the given names are marked for automatic export to the environment of subsequently-executed commands. ksh commands that are preceded by one or two «*» characters (asterisks) are treated specially in the following ways:

• Variable assignment lists preceding the command remain in effect when the command completes.
• I/Oredirections are processed after variable assignments.
• Errors cause a script containing them to abort.
• Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a variable assignment. This assignment means that tilde substitution is performed after the = sign and word splitting and file name generation are not performed.

Examples

In csh, this command sets the environment variable PATH, such that the shell searches for files in the /bin, /usr/bin, /usr/sbin and /usr/local/bin directories, in that order.

Related commands

csh — The C shell command interpreter.
ksh — The Korn shell command interpreter.
setenv — Set the value of an environment variable.
sh — The Bourne shell command interpreter.

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