1. Because the PATH variable defines the directories your shell looks in for commands you type that aren't built into the shell. For instance if you type ls, and ls isn't an internal shell command, it looks through the directories in PATH for an executable file with the same name as the command you typed and tries to execure it. /bin and /usr/bin are used to store commonly used executable files such as ls, grep, chmod, etc.
2. Because the `` quotes are command substitution quotes. the shell will execute the command between them and then substitute is ouput in place of `command` as if you had typed it. `date` tries to run a command named whatever date outputs on your system.
3. Its easiest to use three seperate commands. If it takes longer to figure out how to do something in one command than it takes to type 3 and computing resources aren't an issue because you are only going to do it once or you have a tiny amount of data, why waste your time trying to figure out how to make a complex command work?
4. ${d-*} means if d is unset then assign * to d. see the parameter expansion section of the ksh, sh, or bash man page for more info.
1. You have a very large file, named 'ColMe', tab-delimited, you are asked to process. You are told that each line in 'ColMe' has 7 columns, and that the values in the 5th column are integers. Using shell functions (and standard LINUX/UNIX filters), indicate how you would verify that these... (1 Reply)
Use and complete the template provided. The entire template must be completed. If you don't, your post may be deleted!
1. The problem statement, all variables and given/known data:
Hello,
My name is Jordan and studying at the New Bulgarian University in Sofiya. This is my homework but can... (2 Replies)
1. Write a shell script to print the file names of all files having .txt extension of a given directory after converting to uppercase letters. The input (directory name) should be given as command line argument. The script will also check whether sufficient arguments are passed or not and whether... (1 Reply)
A shell script is a script written for the shell, or command line interpreter, of an operating system. Typical operations performed by shell scripts include file manipulation, program execution, printing text etc.
Shell : In computing, a shell is a piece of software that provides an interface for... (1 Reply)
plz i need code to search about numbers like this :
962785785698
962795565488
962785321565
962777321684
962795979515
i need code to detect just numbers start with "96278"
i need it in awk !!
thanks (1 Reply)
Use and complete the template provided. The entire template must be completed. If you don't, your post may be deleted!
1. The problem statement, all variables and given/known data:
2. Relevant commands, code, scripts, algorithms:
Write a command to display lines ending with the... (1 Reply)
Discussion started by: elh009
1 Replies
LEARN ABOUT MINIX
exec
exec(1) User Commands exec(1)NAME
exec, eval, source - shell built-in functions to execute other commands
SYNOPSIS
sh
exec [argument...]
eval [argument...]
csh
exec command
eval argument...
source [-h] name
ksh
*exec [arg...]
*eval [arg...]
DESCRIPTION
sh
The exec command specified by the arguments is executed in place of this shell without creating a new process. Input/output arguments may
appear and, if no other arguments are given, cause the shell input/output to be modified.
The arguments to the eval built-in are read as input to the shell and the resulting command(s) executed.
csh
exec executes command in place of the current shell, which terminates.
eval reads its arguments as input to the shell and executes the resulting command(s). This is usually used to execute commands generated as
the result of command or variable substitution.
source reads commands from name. source commands may be nested, but if they are nested too deeply the shell may run out of file descrip-
tors. An error in a sourced file at any level terminates all nested source commands.
-h Place commands from the file name on the history list without executing them.
ksh
With the exec built-in, if arg is given, the command specified by the arguments is executed in place of this shell without creating a new
process. Input/output arguments may appear and affect the current process. If no arguments are given the effect of this command is to mod-
ify file descriptors as prescribed by the input/output redirection list. In this case, any file descriptor numbers greater than 2 that are
opened with this mechanism are closed when invoking another program.
The arguments to eval are read as input to the shell and the resulting command(s) executed.
On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways:
1. Variable assignment lists preceding the command remain in effect when the command completes.
2. I/O redirections are processed after variable assignments.
3. Errors cause a script that contains them to abort.
4. Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a vari-
able assignment. This means that tilde substitution is performed after the = sign and word splitting and file name generation are not
performed.
EXIT STATUS
For ksh:
If command is not found, the exit status is 127. If command is found, but is not an executable utility, the exit status is 126. If a redi-
rection error occurs, the shell exits with a value in the range 1-125. Otherwise, exec returns a zero exit status.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWcsu |
+-----------------------------+-----------------------------+
SEE ALSO csh(1), ksh(1), sh(1), attributes(5)SunOS 5.10 17 Jul 2002 exec(1)