2. LINUX Definition: Linux is a free open source Operating System, based on Unix. It is available from many vendors with optional paid for support and provides an increasingly viable alternative to the Win 32, platform.
8. COPY FILE To copy file use Syntax: cp Example: cp myfile yourfile
9. Creates a symbolic link to a file Make links between files, by default, it makes hard links; with the `-s' option, it makes symbolic (or "soft") links. Syntax: ln [Options]... target [Linkname] ln [Options]... target... Directory
10. SENDS FILE CONTENT TO STANDARD OUTPUT To send a file content to standard output use Syntax: cat
13. EXIT FROM A LOOP Exit from a for, while, until, or select loop Syntax: break [n] If n is supplied, the nth enclosing loop is exited. n must be greater than or equal to 1. The return status is zero unless n is not greater than or equal to 1.
14. COMPARE TWO FILE Compare two files, and if they differ, tells the first byte and line number where they differ. You can use the `cmp' command to show the offsets and line numbers where two files differ. `cmp' can also show all the characters that differ between the two files, side by side. Syntax: cmp options... FromFile [ToFile]
15. COMPARE DIFFERENT FILES Display the differences between two files, or each corresponding file in two directories. Each set of differences is called a "diff" or "patch". For files that are identical, diff normally produces no output; for binary (non-text) files, diff normally reports only that they are different. Syntax: diff [options] from-file to-file
16. DIVIDE A FILE INTO SEVERAL PARTS Divide a file into several parts (columns) 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 `-'. Syntax: cut [OPTION]... [FILE]...
17. DISPLAY OR CHANGE THE DATE AND TIME Display or change the date. Syntax: date [option]... [+Format] date [option] [MMDDhhmm[[CC]YY][.ss]] `date' with no arguments prints the current time and date, in the format of the %c directive.
18. DISK CALCULATOR Syntax: dc <options> Option: -e EXPR --expression=EXPR Evaluate EXPR as DC commands. -f FILE --file=FILE Read and evaluate DC commands from FILE.
19. DISPLAY FREE DISK SPACE Disk Free - display free disk space. With no arguments, `df' reports the space used and available on all currently mounted filesystems (of all types). Otherwise, `df' reports on the filesystem containing each argument file. Syntax: df [option]... [file]...
20. PRINT OR SET SYSTEM NAME Print or set system name Syntax: hostname [name] With no arguments, `hostname' prints the name of the current host system. With one argument, it sets the current host name to the specified string. You must have appropriate privileges to set the host name.
27. CURRENT LOGIN NAME Print current login name Syntax: logname Prints the calling user's name, as found in the file`/var/run/utmp', and exits with a status of 0. If there is no `/var/run/utmp' entry for the calling process, `logname' prints an error message and exits with a status of 1.
28. COMMAND HISTORY Command Line history Syntax: history history [n] history -c history -d offset history [-anrw] [filename] history -ps arg
29. DISK USAGE Disk Usage - report the amount of disk space used by the specified files and for each subdirectory. Syntax: du [options]... [file]... With no arguments, `du' reports the disk space for the current directory. Normally the disk space is printed in units of 1024 bytes, but this can be overridden.
30. DISPLAY THE SYSTEM MEMORY Syntax: Free Displays the amount of used and free system memory.
31. CREATE AN ALIAS Syntax: alias [-p] [name[=value] …] unalias [-a] [name ... ] Key: -p Print the current values -a Remove All aliases
33. SEND TO BACKROUND Syntax: bg [PID...] Example: Put the job with job id 0 in the background: bg %0
34. KILLING PROCESS Syntax : kill process_ids kill - signal process_ids kill -l Kills the specified processes, sends the specified processes the specified signal (given as a number or name), or prints a list of available signals.
35. KILL ALL THE PROGRAMS Syntax : killall program killall - signal program Kills all processes that are instances of the specified program or sends the specified signal to all processes that are instances of the specified program.
37. SHUTDOWN THE SYSTEM Syntax : shutdown -r minutes Shuts down the system after the specified number of minutes elapses .
38. SLEEP TIME Syntax : sleep time Causes the command interpreter to pause for the specified number of seconds.
39. An arbitrary precision calculator language Syntax: bc options file... Explanation: bc is a language that supports arbitrary precision numbers with interactive execution of statements. bc starts by processing code from all the files listed on the command line in the order listed. After all files have been processed, bc reads from the standard input. All code is executed as it is read.
40. Run a shell builtin Run a shell builtin, passing it args, and return its exit status. SYNTAX: builtin [shell-builtin [args]] This is useful when defining a shell function with the same name as a shell builtin, retaining the functionality of the builtin within the function.
41. Conditionally perform a command Conditionally perform a command, case will selectively execute the command-list corresponding to the first pattern that matches word. Syntax: case word in [ [(] pattern [| pattern]...) command-list ;;]... esac The `|' is used to separate multiple patterns, and the `)' operator terminates a pattern list. A list of patterns and an associated command-list is known as a clause. Each clause must be terminated with `;;'.
42. Convert a full pathname to just a path Convert a full pathname to just a path Syntax dirname pathname Prints all but the final slash-delimited component of a string (presumably a filename). If PATHNAME is a single component, `dirname' prints `.'
43. Estimate file space usage Disk Usage - report the amount of disk space used by the specified files and for each subdirectory. Syntax du [options]... [file]... With no arguments, `du' reports the disk space for the current directory. Normally the disk space is printed in units of 1024 bytes, but this can be overridden
44. Display message on screen Display message on screen, writes each given STRING to standard output, with a space between each and a newline after the last one. Syntax echo [options]... [string]...
46. Enable and disable builtin shell commands. Syntax: enable [-n] [-p] [-f filename] [-ads] [name …] Options: -a list each builtin with an indication of whether or not it is enabled. -d Delete a builtin loaded with `-f'. -f load the new builtin command name from shared object filename, on systems that support dynamic loading. -n Disable the names listed, otherwise names are enabled.
47. Environment variables Display, set, or remove environment variables, Run a command in a modified environment. Syntax: env [OPTION]... [NAME=VALUE]... [COMMAND [ARGS]...]
48. Exit the shell Exit from a program, shell or log out of a Unix network. Syntax: exit If supported will exit you from the program, shell or log you out of network.
49. Convert tabs to spaces Convert tabs to spaces, write the contents of each given file, to standard output, with tab characters converted to the appropriate number of spaces. If no file is given, or for a file of `-', write to standard input Syntax: expand [options]... [file]...
50. Evaluate expressions Evaluate expressions, evaluates an expression and writes the result on standard output. Syntax: expr expression...
51. Do nothing, unsuccessfully Do nothing, returning a non-zero (false) exit status Syntax: false `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.
52. Send job to foreground Send job to foreground Syntax fg [PID...] Options: If PID is specified, the job with the specified group id is put in the foreground.
54. Comment / Remark Syntax: ### A comment or remark is indicated by starting the line with the # character # This is a description # Another remark command # Another remark Related commands: : (a colon) : [arguments]
55. Run a command script in the current shell Run a command script in the current shell context. Syntax . filename [arguments] source filename [arguments] A dot/period '.' is a synonym for 'source'
56. Print a string until interrupted Syntax: Yes `yes' prints the command line arguments, separated by spaces and followed by a newline, forever until it is killed. If no arguments are given, it prints `y' followed by a newline forever until killed. The only options are a lone `--help' or `--version'.
57. Send a message to another user write Send a message to another user Syntax: write user [ttyname]
58. Print byte, word, and line counts Print byte, word, and line counts, count the number of bytes, whitespace-separated words, and newlines in each given FILE, or standard input if none are given or for a FILE of `-'. Syntax: wc [options]... [file]... Options: -c --bytes --chars Print only the byte counts.
59. CREATE AN ALIAS Syntax: alias [-p] [name[=value] …] unalias [-a] [name ... ] Key: -p Print the current values -a Remove All aliases
60. EXCUTE A COMMAND Syntax: exec [-cl] [-a name] [command [arguments]] Options: -l Place a dash at the beginning of the zeroth arg passed to command. -c Causes command to be executed with an empty environment. -a The shell passes name as the zeroth argument to command.
61. CONVERT AND COPY A FILE Convert and copy a file, write disk headers, boot records, create a boot floppy. dd can make an exact clone of an (unmounted) disk, this will include all blank space so the output destination must be at least as large as the input. Syntax dd [Options]
62. PRINT KERNAL MESSAGE Print kernel (and driver) messages, control the kernel ring buffer. Syntax: dmesg [ -c ] [ -n level ] [ -s bufsize ]
