Commands and Keywords that every Linux user MUST know Part 1

Here is the list of keywords and phrases in alphabetical order that every Linux newbie should learn or at least have on file :

alias -- define or display aliases.
The alias utility will create or redefine alias definitions or write the values of existing alias definitions to standard output. An alias definition provides a string value that shall replace a command name when it is encountered.

aspell -- interactive spell checker.
aspell is a utility program that connects to the Aspell library so that it can function as an ispell -a replacement, as an independent spell checker, as a test utility to test out Aspell library features, and as a utility for managing dictionaries used by the library.

at -- execute commands at a later time.
The at utility will read commands from standard input and group them together as an at-job, to be executed at a later time.

awk -- find and replace text in file(s).
AWK is a language for processing files of text. A file is treated as a sequence of records, and by default each line is a record. Each line is broken up into a sequence of fields, so we can think of the first word in a line as the first field, the second word as the second field, and so on. An AWK program is of a sequence of pattern-action statements. AWK reads the input a line at a time. A line is scanned for each pattern in the program, and for each pattern that matches, the associated action is executed.

basename -- strip directory and suffix from filenames.
If SUFFIX is specified and is identical to the end of NAME, it is removed from NAME as well. Note that since trailing slashes are removed prior to suffix matching, SUFFIX will do nothing if it contains slashes. `basename' prints the result on standard output.

bg -- run jobs in the background.
Using bg to place a job into the background will cause its process ID to become "known in the current shell execution environment", as if it had been started as an asynchronous list.

break -- exit from for, while, or until loop.
The break utility shall exit from the smallest enclosing for, while, or until loop, if any; or from the nth enclosing loop if n is specified. The value of n is an unsigned decimal integer greater than or equal to 1.

bzip2/bunzip2 -- bzip2, bunzip2 - a block-sorting file compressor.
bzip2 compresses files using the Burrows-Wheeler block sorting text compression algorithm, and Huffman coding. Compression is generally considerably better than that achieved by more conventional LZ77/LZ78-based compressors, and approaches the performance of the PPM family of statistical compressors.

bzip2recover -- recovers data from damaged bzip2 files.

cal -- displays a calendar.
A single parameter specifies the year (1 - 9999) to be displayed; note the year must be fully specified: “cal 89” will not display a calendar for 1989. Two parameters denote the month (1 - 12) and year. Three parameters denote the day (1-31), month and year, and the day will be highlighted if the calendar is displayed on a terminal. If no parameters are specified, the current month's calendar is displayed.

case -- Evaluate one of several scripts, depending on a given value.
The case command matches string against each of the patList arguments in order. Each patList argument is a list of one or more patterns. If any of these patterns matches string then case evaluates the following body argument by passing it recursively to the Tcl interpreter and returns the result of that evaluation. Each patList argument consists of a single pattern or list of patterns. Each pattern may contain any of the wild-cards described under string match. If a patList argument is default, the corresponding body will be evaluated if no patList matches string. If no patList argument matches string and no default is given, then the case command returns an empty string.

cat -- reads the text of one or more files.

cd -- change current directory.

cdrecord -- record audio or data Compact Disks or Digital Versatile Disks from a master.
Cdrecord is completely based on SCSI commands but this is no problem as all CD/DVD/BluRay writers ever made use SCSI commands for the communication. Even ATAPI drives are just SCSI drives that inherently use the ATA packet interface as SCSI command transport layer build into the IDE (ATA) transport. You may need to specify an alternate transport layer on the command line if your OS does not implement a fully integrated kernel driver subsystem that allows to access any drive using SCSI commands via a single unique user interface.

cfdisk* -- split HDD into a partitions.
* it needs to be executed as Super User a.k.a root
cfdisk is a curses based program for partitioning any hard disk drive. Typical values of the device argument are: /dev/hda [default]
/dev/hdb
/dev/sda
/dev/sdb
/dev/sdc
/dev/sdd

chfn -- change user name and information.
The chfn command changes user fullname, office number, office extension, and home phone number information for a user´s account. This information is typically printed by finger and similar programs. A normal user may only change the fields for his/her own account, subject to the restrictions in /etc/login.defs. (The default configuration is to prevent users from changing their fullname.) The superuser may change any field for any account. Additionally, only the superuser may use the -o option to change the undefined portions of the GECOS field.

chsh -- change login shell.
The chsh command changes the user login shell. This determines the name of the user´s initial login command. A normal user may only change the login shell for her own account, the superuser may change the login shell for any account.

chgrp* -- change group ownership
* it needs to be executes as SuperUser a.k.a root
Change the group of each FILE to GROUP. With --reference, change the group of each FILE to that of RFILE.

chmod -- change permissions for access to a file.
chmod changes the file mode bits of each given file according to mode, which can be either a symbolic representation of changes to make, or an octal number representing the bit pattern for the new mode bits.

chown -- change file owner and group.
chown changes the user and/or group ownership of each given file. If only an owner (a user name or numeric user ID) is given, that user is made the owner of each given file, and the files' group is not changed. If the owner is followed by a colon and a group name (or numeric group ID), with no spaces between them, the group ownership of the files is changed as well. If a colon but no group name follows the user name, that user is made the owner of the files and the group of the files is changed to that user's login group. If the colon and group are given, but the owner is omitted, only the group of the files is changed; in this case, chown performs the same function as chgrp. If only a colon is given, or if the entire operand is empty, neither the owner nor the group is changed.

chroot -- run command or interactive shell with special root directory.
Ordinarily, file names are looked up starting at the root of the directory structure, i.e., `/'. `chroot' changes the root to the directory NEWROOT (which must exist) and then runs COMMAND with optional ARGS. If COMMAND is not specified, the default is the value of the `SHELL' environment variable or `/bin/sh' if not set, invoked with the `-i' option. COMMAND must not be a special built-in utility.

cksum -- checksum and count the bytes in a file.
cksum computes a cyclic redundancy check (CRC) checksum for each given FILE, or standard input if none are given or for a FILE of `-'.

clear -- clear the terminal screen.
clear clears your screen if this is possible. It looks in the environment for the terminal type and then in the terminfo database to figure out how to clear the screen.

cmp -- compare two files byte by byte.
In the simplest case, two file names FROM-FILE and TO-FILE are given, and `diff' compares the contents of FROM-FILE and TO-FILE. A file name of `-' stands for text read from the standard input. As a special case, `diff - -' compares a copy of standard input to itself.

comm -- compare two sorted files line by line.
comm writes to standard output lines that are common, and lines that are unique, to two input files; a file name of `-' means standard input.

command -- execute a simple command.
The command utility will cause the shell to treat the arguments as a simple command, suppressing the shell function lookup that is described in Command Search and Execution, item 1b.

continue -- continue for, while, or until loop.
The continue utility will return to the top of the smallest enclosing for, while, or until loop, or to the top of the nth enclosing loop, if n is specified. This involves repeating the condition list of a while or until loop or performing the next assignment of a for loop, and re-executing the loop if appropriate.

cp -- copy files and directories.
cp copies files (or, optionally, directories). The copy is completely independent of the original. You can either copy one file to another, or copy arbitrarily many files to a destination directory.

crontab -- maintain crontab files for individual users.
Crontab is the program used to install, deinstall or list the tables used to drive the cron daemon in ISC Cron. Each user can have their own crontab, and though these are files in /var, they are not intended to be edited directly.

csplit -- split a file into sections determined by context lines.
csplit creates zero or more output files containing sections of INPUT (standard input if INPUT is `-').

curl -- transfer a URL.
curl is a tool to transfer data from or to a server, using one of the supported protocols (HTTP, HTTPS, FTP, FTPS, SCP, SFTP, TFTP, DICT, TELNET, LDAP or FILE). The command is designed to work without user interaction.

cut -- remove sections from each line of files.
cut writes to standard output selected parts of each line of each input file, or standard input if no files are given or for a file name of `-'.

date -- print or set the system date and time.
Display the current time in the given FORMAT, or set the system date.

dc -- an arbitrary precision calculator.
dc is a reverse-polish desk calculator which supports unlimited precision arithmetic. It also allows you to define and call macros. Normally dc reads from the standard input; if any command arguments are given to it, they are filenames, and dc reads and executes the contents of the files before reading from standard input. All normal output is to standard output; all error output is to standard error.

dd -- convert and copy a file.
dd copies a file (from standard input to standard output, by default) with a changeable I/O block size, while optionally performing conversions on it.

df -- report file system disk space usage.
Disk space is shown in 1K blocks by default, unless the environment variable POSIXLY_CORRECT is set, in which case 512-byte blocks are used.

diff -- compare files one by one (shows the difference between two files).
In the simplest case, two file names FROM-FILE and TO-FILE are given, and `diff' compares the contents of FROM-FILE and TO-FILE. A file name of `-' stands for text read from the standard input. As a special case, `diff - -' compares a copy of standard input to itself.

diff3 -- compare and show the difference between 3 files.

dir -- list directory contents.
List information about the FILEs (the current directory by default). Sort entries alphabetically if none of -cftuvSUX nor --sort.

dircolors -- color setup for ls.
dircolors outputs a sequence of shell commands to set up the terminal for color output from `ls' (and `dir', etc.).

dirname -- strip non-directory suffix from file name.
dirname prints all but the final slash-delimited component of a string (presumably a file name).

du -- estimate file space usage.
Summarize disk usage of each FILE, recursively for directories.

echo -- display a line of text.
echo' writes each given STRING to standard output, with a space between each and a newline after the last one.

ed -- text editor
ed is a line-oriented text editor. It is used to create, display, modify and otherwise manipulate text files.

egrep -- print lines matching a pattern.
egrep is the same as grep -E.

eject -- eject removable media.
Eject allows removable media (typically a CD-ROM, floppy disk, tape, or JAZ or ZIP disk) to be ejected under software control. The command can also control some multi-disc CD-ROM changers, the auto-eject feature supported by some devices, and close the disc tray of some CD-ROM drives.

env -- run a program in a modified environment.

eval -- construct command by concatenating arguments.
The eval utility will construct a command by concatenating arguments together, separating each with a . The constructed command shall be read and executed by the shell.

exec -- execute commands and open, close, or copy file descriptors.
The exec utility will open, close, and/or copy file descriptors as specified by any redirections as part of the command.

exit -- cause the shell to exit.

expand -- convert tabs to spaces.
Convert tabs in each FILE to spaces, writing to standard output. With no FILE, or when FILE is -, read standard input.

export -- set the export attribute for variables.
The shell will give the export attribute to the variables corresponding to the specified names, which shall cause them to be in the environment of subseâ€ quently executed commands. If the name of a variable is followed by = word, then the value of that variable shall be set to word.

expr -- evaluate expressions.
expr evaluates an expression and writes the result on standard output. Each token of the expression must be a separate argument.

factor -- factor numbers.

flase -- do nothing, unsuccessfully.
false' does nothing except return an exit status of 1, meaning "failure". It can be used as a place holder in shell scripts where an unsuccessful command is needed. In most modern shells, `false' is a built-in command, so when you use `false' in a script, you're probably using the built-in command.

fdformat -- Low-level formats a floppy disk.

fdisk* -- Partition table manipulator.
* it needs to be executed as SuperUser a.k.a. root
Hard disks can be divided into one or more logical disks called partitions. This division is described in the partition table found in sector 0 of the disk.

fg -- run jobs in the foreground.
If job control is enabled, fg will move a background job from the current environment into the foreground.

file -- determine file type.
file tests each argument in an attempt to classify it. There are three sets of tests, performed in this order: filesystem tests, magic tests, and language tests. The first test that succeeds causes the file type to be printed.

fgrep -- print lines matching a pattern
fgrep is the same as grep -F

find -- search for files in a directory hierarchy
See Howto Find files with find
For additional questions or comment please refer to our FORUM

de.li.cio.us