This appendix is a quick reference for essential UNIX/Linux utilities available

Transcription

1 APPENDIX B SYNTAX GUIDE TO UNIX/LINUX COMMANDS This appendix is a quick reference for essential UNIX/Linux utilities available on most systems. lists the commands alphabetically, including the command name, its purpose, and useful options. Table B-2 lists the UNIX/Linux utilities by category. Table B-3 summarizes the vi editor commands, and Table B-4 summarizes the Emacs editor commands. The UNIX/Linux command syntax uses the format diagrammed in Figure B-1. $ command [-options] arguments File names or paths Single-letter options, preceded by a minus sign Figure B-1 Command syntax format Command name System prompt For example, to use the ls command to see a directory s contents and use the -a option to view hidden files plus the -l option to view a long listing of file detail, you would enter: ls -al or ls -a -l In another example, to make a backup copy using the cp command of the file myorginalfile.txt to the file clonecopy.txt (where the file names are arguments), you would enter: cp myorginalfile.txt clonecopy.txt 625

2 626 Appendix B Syntax Guide to UNIX/Linux Commands Common UNIX/Linux commands alias Creates an alias for a command Include in the.bashrc file for access each time you log in; example: alias dir= ls -1. -p prints all aliases. awk cal cat cd chmod Starts the Awk program to format output Shows the system calendar for a specified year or month Creates files, concatenates files, or can be used to display the contents of files Changes directories Changes security mode of a file or directory (r: read, w: write, x: executable); sets file permissions for specified users (u: user, g: group, o: others, a: all) -f indicates code is coming from a disk file, not the keyboard. -F specifies the field separator. -1 shows a single month. -3 shows three months beginning with the previous month. -j displays the calendar in Julian date format. -s shows Sunday as the first day in the week. -m shows Monday as the first day in the week. -y shows all of the months for the current year. cat -n displays line numbers. cat filename displays the contents of a file. cat > filename creates a new file or enables you to overwrite the contents of an existing file. cat >> filename creates a new file or enables you to add information to an existing file. cat file1 file2 > file3 concatenates two existing files into one new file. cd by itself takes the user to his home directory.. Changes to the current working directory... Changes to the parent directory. + assigns permissions. - removes permissions. chmod a+x sets the execute bit for owner, group, and other (all). clear Clears the screen Commonly aliased to cls; see the alias command. comm Compares sorted files and shows differences comm file1 file2 compares the files line by line. -1 does not display unique lines in the first file. -2 does not display unique lines in the second file. -3 does not display unique lines in both files.

3 Syntax Guide to UNIX/Linux Commands 627 Common UNIX/Linux commands (continued) cp Copies files from one directory to another -b makes a backup of the destination file, if an original one already exists (so you have a backup if overwriting a file). -i requests confirmation if the target file already exists. -r copies directories to a new directory. -s creates a symbolic link or name at the destination rather than a physical file. -u overwrites an existing file only if the source is newer than the file in the current destination. cut date diff Selects and extracts specified columns or fields from a file Displays the system date Compares and selects differences in two files or directories. (dot) Represents the current directory (the. is a link to the inode for the current directory).. (dot dot) Represents the parent directory (the.. is a link to the inode for the parent directory) echo Displays the specified arguments on the output device emacs Starts the Emacs editor exit or logout Logs out of your current session -c specifies the character position. -d specifies the field separator. -f specifies the field position. -u displays the time in Greenwich Mean Time. diff /dir1 /dir2 compares the file entries in both directories and shows only the missing files for each directory. -b ignores blanks that repeat. -B does not compare for blank lines. -i ignores case. -c shows lines surrounding the line that differs (for context). -y displays the differences side-by-side in columns. Used mostly in specifying that something happened in the current directory; for example, cp /dir/file. copies the file to the current directory. Used for changing to a different directory, either the parent of the current (cd..) or up one directory and down a different tree (cd../dir2/dir3). echo $VAR, where VAR is the variable name, echoes the data from an environment variable to standard output; can also be used in scripts and programs. Ctrl+d also logs the user out of a session or a subshell and back to the parent shell. B

4 628 Appendix B Syntax Guide to UNIX/Linux Commands Common UNIX/Linux commands (continued) export Makes a variable an environment variable; and exports a specified list of variables to other shells -n can be used to undo the export. -p lists the exported variables. find fuser grep head history Locates files that match a given value Displays the process ID (PID) of processes using a given resource Selects lines or rows that match a specified pattern Displays the first few lines of a file Lists all the commands contained in the bash history file -amin n finds files accessed more recently than n minutes ago. -atime n finds files last accessed n*24 hours ago. -fstype type finds files that exist only on the specified file system type, such as ext3. -iname pattern finds files with names that match a pattern. -inum inode# finds files with inodes that match inode. -name specifies the name of the files you want to locate but the search is case sensitive. -mmim m displays files that have been changed within the last n minutes. -mtime n displays files that have been changed within the last n days. -size n displays files of size n. -user uname finds files owned by user matching uname. Useful for finding which users have mounted a drive that needs maintenance; for example, fuser vu /mnt shows all processes accessing a resource and their associated user names. -c only counts the number of lines matching the pattern instead of showing them. -i ignores case. -l lists only file names that contain the pattern. -L lists only file names that do not contain the pattern. -n displays line numbers. -r searches through files under all subdirectories. -v displays lines in a file that do not match the specified pattern. Shows the first 10 lines by default. -n n displays the first n lines of the specified file. Bash history file is.bash_history by default and resides in the user s home directory; default number of last commands kept in the history file is 500.

5 Syntax Guide to UNIX/Linux Commands 629 Common UNIX/Linux commands (continued) join Combines files having a common field -1 fieldnum specifies the common field in file 1 on which to join. -2 fieldnum specifies the common field in file 2 on which to join. -a n produces a line for each unpairable line in file n, where n =1or2. -e string replaces the empty fields for the unpairable line with the string specified by string. -o specifies a list of fields to be output. -t specifies the field separator character. By default, this is a blank, tab, or newline character. Multiple blanks and tabs count as one field separator. kill Ends a process -9 destructively ends a process. -HUP causes the service or daemon to stop (hang up) and restart, which causes the rereading of its configuration files; often used to make changes to a running service. last less let ln Shows the login history of all users on the system Scrolls long files to screen Stores the results of arithmetic operations in a variable Creates symbolic or hard links to files -a displays the host name from which the user connected. -d shows the corresponding IP address for remotes. Allows for scrolling up and down in a file, whereas the more command only allows advancing down a file. By default, creates a hard link, which is another name for a particular inode. -s creates a symbolic link to a file, like a shortcut. lpr Prints a file -P printer prints on a specified printer. #n prints a specified number of copies of the file. -r deletes a print file after it is printed. ls Lists a directory s contents, including its files and subdirectories -a lists hidden files. -l lists files in long format, showing detailed information. -r lists files in reverse alphabetic order. -s shows the size of each file. -S sorts the listing by file size. -t sorts by the time when the file or directory was last modified. -X sorts by extension. B

6 630 Appendix B Syntax Guide to UNIX/Linux Commands Common UNIX/Linux commands (continued) lspci Displays information about all PCI buses on the system (but you must be logged in as root) -v is verbose output. -vv is very verbose output. -t shows a tree-like structure of PCI bus/devices. man mkdir more mount mv passwd paste Displays the online manual for the specified command Makes a new directory Displays a long file one screen at a time Connects the file system to the directory tree in the specified location Moves or renames files Changes your UNIX/Linux password Combines the contents of one or more files to output to the screen or to another file (by default, the pasted results appear in columns separated by tabs) -d prints information for debugging. -f gives a short description of the command (same as using the whatis command). -K finds a certain string by searching through all of the man information. -t formats the output for printing using ghostscript. -v verifies the file is made. Pressing the spacebar advances one screen at a time; pressing Enter advances one line at a time. -r indicates that the mounted partition s device is read-only. -a mounts all possible file systems from /etc/fstab. -t specifies the type of file system to mount. -f never prompts before overwriting existing files and directories. -i displays a warning prompt before overwriting a file with the same name. -u overwrites a destination file with the same name, if the source file is newer than the one in the destination. Users can change only their own password; the root user can change others passwords. -e expires a password causing the user to have to recreate it. -l locks an account. -S displays the password status of an account. -d enables you to specify a different separator (other than a tab) between columns. -s causes files to be pasted one after the other instead of in parallel.

7 Syntax Guide to UNIX/Linux Commands 631 Common UNIX/Linux commands (continued) pr Formats a specified file before printing or viewing -a displays output in columns across the page, one line per column. -d double-spaces the output. -h customizes the header line. -ln sets the number of lines per page. printenv Prints a list of environment variables printf Tells the Awk program what action to take for formatting and printing information ps Shows processes on a system -a shows all running processes. -u shows the user associated with a process. -x shows background system processes. pwd Displays your current path rm Removes a file -i requests confirmation before deleting a file. -r deletes a specified directory and its contents. rmdir Removes a directory -v provides a message to verify the directory is removed. sed set sh Specifies an editing command or a script file containing sed commands Establishes specific operational conditions in the Bash shell Executes a shell script -a \ appends text after a line or a script file containing sed commands. -d deletes specified text. -e specifies multiple commands on one line. -n indicates line numbers on which to work. -p displays lines. -s substitutes specified text. -a exports all shell variables after they are assigned. -n takes commands without executing them, so you can debug errors. -o sets a particular shell mode when used with noclobber as the argument, it prevents files from being overwritten by use of the > operator. -u yields an error message when there is an attempt to use an undefined variable. -v displays command lines as they are executed. Makes using./ or #!/bin/sh unnecessary. -n reads commands without executing them. -v displays lines of code as executed. -x displays commands and arguments as executed. B

8 632 Appendix B Syntax Guide to UNIX/Linux Commands Common UNIX/Linux commands (continued) sort Sorts and merges multiple files + designates the position that follows an offset (+) as a character position, not a field position. -b ignores leading blank characters. -d sorts in dictionary order. -f ignores differences based on uppercase and lowercase. -g sorts by numeric (general) order. -k n sorts on the key field specified by n. -m merges input files that have been previously sorted (does not perform a sort). -n sorts numbers arithmetically. -o redirects output to the specified file. -r sorts in reverse order. -t indicates that a specified character separates the fields. startx Starts the X Window System tail Displays the last few lines of a file By default, displays the last 10 lines of a file. -n n displays the last n lines of the specified file. test Compares values and validates file existence! tests for logical negation. -a tests for a logical AND relationship. -b tests if a file exists and is a block special file (which is a block-oriented device, such as a disk or tape drive). -c tests if a file exists and is a character special file (that is, a character-oriented device, such as a terminal or printer). -d tests if a file exists and is a directory. -e tests if a file exists. -eq tests if equal to. -f tests if a file exists and is a regular file. -ge tests if greater than or equal to. -gt tests if greater than. -le tests if less than or equal to. -lt tests if less than. -n tests for a nonzero string length. -ne tests if not equal to. -o tests for a logical OR relationship. -r tests if a file exists and is readable. -s tests if a file exists and its size is greater than zero. string tests for a nonzero string length. string1 = string2 tests two strings for equality. string1!= string2 tests two strings for inequality. -w tests if a file exists and is writable. -x tests if a file exists and is executable. -z tests for a zero-length string.

9 Syntax Guide to UNIX/Linux Commands 633 Common UNIX/Linux commands (continued) top Displays a list of the most CPU-intensive tasks -c displays the command that initiated each process. -i ignores any idle processes. -q displays output continually, with no delay between outputs. (Use with caution! Try the spacebar for periodic updates.) -s causes the top command to run in secure mode, disabling its interactive commands. -S runs top in cumulative mode, which displays the cumulative CPU time used by a process. touch tput tr trap tty umask umount uniq Changes a file s time and date stamp Formats screen text Translates characters Executes a command when a specified signal is received from the operating system Displays terminal pathname Sets file permissions for multiple files Disconnects the file system partitions from the directory tree Removes consecutive duplicate lines from one file and writes the result to another file -a specifies that only the access date and time are to be updated. -m specifies that only the modification date and time are to be updated. -c specifies that no files are to be created. clear clears the screen. cols prints the number of columns on the current terminal. cup moves the screen cursor to a specified row and column. rmso disables boldface output. smso enables boldface output. -d deletes input characters found in string1 from the output. -s checks for sequences of string1 repeated consecutive times. -l displays a listing of signal numbers and their signal designations. If mounted or being accessed by another user, see the fuser command to force unmounting of the resource. -u outputs only the lines of the source file that are not duplicated. -d outputs one copy of each line that has a duplicate, and does not show unique lines. -i ignores case. -c starts each line by showing the number of each instance. B

10 634 Appendix B Syntax Guide to UNIX/Linux Commands Common UNIX/Linux commands (continued) wc Counts the number of lines, bytes, or words -c counts the number of bytes or characters. -l counts the number of lines. -w counts the number of words. in a file whatis Displays a brief description of a command whereis w who Table B-2 Locates source, binary, and manual entries for the specified string or command Displays users currently on the system Shows who is currently logged in to a system UNIX/Linux utilities by category -b searches for binary entries only. -m searches for manual entries only. -s searches for source entries only. Shows user s originating host, idle time, her current command, CPU utilization, and login time. -b verifies when the system was last booted. -H displays column headings. -q displays a quick list of users. -u displays session idle times. Command Brief Description of Function File-Processing Utilities awk Processes files cat Displays files (and is used with other tools to concatenate files) cmp Compares two files comm Compares sorted files, and shows differences cp Copies files cpio Copies and backs up files to an archive cut Selects characters or fields from input lines dd Copies and converts input records diff Compares two text files, and shows differences dump Backs up files fdformat Formats a floppy disk at a low level file Displays the file type find Finds files within file tree fmt Formats text very simply grep Matches patterns in a file groff Processes embedded text formatting codes gzip Compresses or decompresses files head Displays the first part of a file (first 10 lines by default) ispell Checks one or more files for spelling errors (on some systems, this command might not be documented via the man command)

11 Syntax Guide to UNIX/Linux Commands 635 Table B-2 UNIX/Linux utilities by category (continued) Command Brief Description of Function less Displays files allowing for scrolling forward and backward (pauses when screen is full) ln Creates a link to a file lpr Sends a file to a printer or printer device ls Lists file and directory names and attributes man Displays documentation for commands mkbootdisk Creates a CD (or floppy disk on older distributions) from which to boot a system mkdir Creates a new directory mkfs Builds a UNIX/Linux file system more Displays the contents of a file allowing for scrolling forward (pauses when screen is full) mount Mounts file systems and devices mv Renames and moves files and directories newfs Creates a new file system (used in UNIX systems in particular) od Formats and displays data from a file in octal, hexadecimal, and ASCII formats paste Combines the contents of one or more files to output to the screen or to another file (by default, the pasted results appear in columns separated by tabs) pr Formats text files for printing and displays them pwd Shows the directory you are in rdev Queries or sets the root image device restore Restores files (from a dump) rm Removes files rmdir Removes directories sed Edits streams (noninteractive) sort Sorts or merges files tail Displays the last lines of files (last 10 lines by default) tar Copies and backs up files to a tape archive touch Changes file modification dates and times (and can be used to create a new file) uniq Displays unique lines of a sorted file wc Counts lines, words, and bytes whereis Locates information about a specific file System Status Utilities date Sets and displays date and time df Displays the amount of free space remaining on disk du Summarizes file space usage file Determines file type (for example, shell script, executable, ASCII text, and others) finger Displays detailed information about users who are logged in free Displays amount of free and used memory in the system B

12 636 Appendix B Syntax Guide to UNIX/Linux Commands Table B-2 UNIX/Linux utilities by category (continued) Command Brief Description of Function edquota Displays user disk quotas and enables them to be changed kill Terminates a running process ps Displays process status by process identification number and name sleep Suspends execution for a specified time top Dynamically displays the status of processes in real time, focusing on those processes that are using the most CPU resources uname Shows information about the operating system (use the -r option to determine your kernel version) vmstat Shows information about virtual memory use w Displays detailed information about the users who are logged in who Displays brief information about the users who are logged in Network Utilities ftp Transfers files over a network ifconfig Sets up a network interface netstat Shows network connection information nfsstat Shows statistics for Network File System (NFS; file upload and download) activity ping Polls another network station (using TCP/IP); great for a fast determination about whether your network connection is working rcp Remotely copies a file from a network computer rlogin Logs in to a remote computer route Displays routing table information, and can be used to configure routing rsh Executes commands on a remote computer showmount Lists clients that have mounted volumes on a server telnet Connects to a remote computer on a network traceroute Shows the route along a network between the source device and the destination, such as from a computer to a server wvdial Controls a modem dialer for dial-up connections over a phone line Communications Utilities mail Sends electronic mail messages mesg Denies (mesg n) or accepts (mesg y) messages talk Lets users simultaneously type messages to each other wall Sends a message to all logged in users (who have permissions set to receive messages) write Sends a message to another user Security Utilities chgrp Changes the group associated with a file or the file s group ownership chmod Changes the access permissions of a file or directory chown Changes the owner of a file ipchains Manages a firewall and packet filtering (do not use if you are using iptables instead) iptables Manages a firewall and packet filtering (do not use if you are using ipchains instead)

13 Syntax Guide to UNIX/Linux Commands 637 Table B-2 UNIX/Linux utilities by category (continued) Command Brief Description of Function passwd Changes a password Programming Utilities configure Configures program source code automatically g++ Compiles a C++ program gcc Compiles acprogram make Maintains program source code patch Updates source code Source Code Management Utilities ci Creates changes in Revision Control Systems (RCS) co Retrieves an unencoded revision of an RCS file cvs Manages concurrent access to files in a hierarchy rcs Creates or changes the attributes of an RCS file rlog Prints a summary of the history of an RCS file Miscellaneous Utilities at Executes a command or script at a specified time atq Shows the jobs (commands or scripts) already scheduled to run atrm Enables you to remove a job (command or script) that is scheduled to run batch Runs a command or script, and is really a subset of the at command that takes you to the at> prompt, if you type only batch (in Fedora, Red Hat Enterprise Linux, and SUSE, a command or script is run when the system load is at an acceptable level) cal Displays a calendar for a month or year cd Changes to a directory crontab Schedules a command to run at a preset time expr Evaluates expressions (used for arithmetic and string manipulations) fsck Checks and fixes problems on a file system (repairs damage) printenv Prints environment variables tee Clones output stream to one or more files tr Replaces specified characters (a translation filter) tty Displays terminal pathname xargs Converts standard output of one command into arguments for another B Table B-3 vi editor commands Command Purpose :! Leaves vi temporarily $ Goes to the end of the line. (repeat) Repeats your most recent change / Searches forward for a pattern of characters 0 (zero) Goes to the beginning of the line d$ or D Deletes from the cursor to the end of the line d0 Deletes from the cursor to the start of the line dd Deletes the current line

14 638 Appendix B Syntax Guide to UNIX/Linux Commands Table B-3 vi editor commands (continued) Command Purpose dw Deletes the word starting at the cursor; if the cursor is in the middle of the word, deletes from the cursor to the end of the word H Goes to the upper-left corner of the screen i Switches to insert mode L Goes to the last line on the screen p Pastes text from the clipboard :q Cancels an editing session :q! Cancels an editing session and exits :r Reads text from one file and adds it to another :set Turns on certain options, such as line numbering u Undoes your most recent change :w Saves a file and continues working :wq Writes changes to disk and exits vi :x Saves changes and exits vi x Deletes the character at the cursor location yy Copies (yanks) text to the clipboard ZZ In command mode, saves changes and exits vi Table B-4 Command Alt Commands Alt+< Alt+> Alt+b Alt+d Alt+f Alt+q Alt+t Alt+u Alt+w Alt+x doctor Ctrl Commands Ctrl+@ Ctrl+a Emacs editor commands Purpose Moves the cursor to the beginning of the file Moves the cursor to the end of the file Moves the cursor back one word Deletes the current word Moves the cursor forward one word (moving space to space between words) Reformats current paragraph using word wrap so that lines are full If the cursor is under the first character of the word, transposes the word with the preceding word; if the cursor is not under the first character, transposes the word with the following word Capitalizes all letters from the cursor position in a word to the end of that word Marks the end of a text block to copy (after you have marked the start of text with Ctrl+spacebar) and briefly scrolls up to where you set the beginning mark Enters doctor mode to play a game in which Emacs responds to your statements with questions (Save your work first. Not all versions support this mode) Marks the cursor location; after moving the cursor, you can move or copy text to the mark Moves the cursor to the beginning of the line

15 Syntax Guide to UNIX/Linux Commands 639 Table B-4 Command Ctrl+b Ctrl+d Ctrl+e Ctrl+f Ctrl+g Ctrl+h Ctrl+k Ctrl+n Ctrl+p Ctrl+t Ctrl+v Ctrl+w Ctrl+y Ctrl+h, t Ctrl+x, Ctrl+c Ctrl+x, Ctrl+s Ctrl+x, u Ctrl+Del Ctrl+spacebar Emacs editor commands (continued) Purpose Moves the cursor back one character Deletes the character under the cursor Moves the cursor to the end of the line Moves the cursor forward one character Cancels the current command Runs online help Deletes text to the end of the line Moves the cursor to the next line Moves the cursor to the preceding line Transposes the character before the cursor and the character under the cursor Scrolls down one screen Deletes the marked text; press Ctrl+y to restore deleted text Inserts text from the file buffer, and places it after the cursor Runs a tutorial about Emacs Exits Emacs Saves the file Undoes the last change Deletes text from the current cursor location to the end of the current word Marks the beginning of text, such as to copy the text (use Alt+w to mark the end of the text) B

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