Bash - (Simple) (Command | Expression)
Table of Contents
About
Process - Command (Command line) in bash are also the expression unit
A command (or an expression) is a sequence of words separated by blanks, terminated by a control operator.
For the builtin bash function command, see Bash - Command (The Builtin command command)
Each command execution has an environment.
Articles Related
Search Order
The default order for command lookup is:
- built-ins (If you want to disable a builtin command, see the command Bash - Enable, disable or print Builtin command),
- Bash - Disk Command (ie with scripts and executables last)
There are three built-ins that you can use to override this order:
- Bash - Command (The Builtin command command) - Removes alias and function lookup. Only built-ins and commands found in the search path are executed
- Bash - Builtin Commands - Looks up only built-in commands, ignoring functions and commands found in PATH
- and Bash - Enable, disable or print Builtin command - Enables and disables shell built-ins
Exit Status
The return status (of Exit Status) is:
- its exit status as provided by the POSIX 1003.1 waitpid function,
- or 128+n if the command was terminated by signal n.
Management
Execution
Check availibilty
# Check the command $1
function check_command() {
command -v $1 -v 2>&1 > /dev/null || { echo >&2 "I require $1 but it's not installed. Aborting."; exit 1; }
}
Help
Alias
To create a shortcut of a command with parameters, see Bash - Alias (of a command) - Builtin command
List the history of the command called
history
With the command history:
$history
you will get an history of the command
1000 cat installation_overview_di.txt
1001 fc -l 999
1002 man fc
1003 history
1004 history|grep NQS
1005 ls -al
1006 ls -al
1007 dir
1008 history
The exclamation mark start a history command substitution, except when followed by a space character, tab, newline, = or (.
- !! execute the last command executed. It would execute the history command (1008)
- !str - Re runs the last command that you ran that starts with str (string). For instance, !ls would execute the last ls command ie the command 1006
- !1007 Rerun the command 1007. A dir command in our case.
- !-2 Refer to the current command line minus 2. Ie the command 1007 (dir)
- !?str? - Refer to the most recent command containing str (string). For instance, !?al? will start the command 1000 <note warning>and not the command 1006 because it does not take into account the option !</note>
fc
The 'fc' utility lists or edits and re-executes, commands previously entered to an interactive sh.
fc -l 999
will list the last 999 command
Ctrl + r
List of common command
Command | Description |
---|---|
Network | |
ifconfig | To detect the IP Adress |
netstat -rn | routing table |
Ctrl+C | interruption of script |
hostname name | To set the hostname, name is the system name you want for your local machine (fully qualified domain name or not) |
Navigation / NFS | |
mkdir | make directory |
cd | change directory ( cd .. is the shortcut for moving up one directory level). ex. cd “Entreprise Linux 2007” |
ls | ls -a show the cached file |
mv | Changes the names of directories and subdirectories mv old_name new_name |
pwd | display the name of the current directory. The pwd command stands for “print working directory” |
which | give the path of a file. Ex : “which java” return “/usr/bin/java” |
ln | make links (short cut) between files |
df | Disk Free to know the used space (Example: df -h where h stands for human readable) |
rm | delete a file |
rmdir | delete a directory |
CD Rom | |
mount | On redhat linux 6 or below: mount /dev/hdc /mnt/cdrom and for above versions: mount /dev/cdrom /mnt/cdrom |
Environment | |
echo | To get the value of en environment variable (ex.: echo $ARBORPATH) |
env or set | A long list of bash environment variables appears |
Security | |
whoami | Return the current user |
Process | |
top | display top CPU processes |
Text Manipulation | |
grep | filters content based on certain strings |
sed | search and replace |
awk | sed and grep in one tool |