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# Author: sdwsk |
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# Date: 2015/12/19 |
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# 0.1 Directory structure. |
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/dev/ # devices |
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/etc/ # system wide configuration files |
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/etc/rsyslog.conf # log config |
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/proc/ # files used by a kernel |
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/bin/ # binaries - used by everyone |
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/sbin/ # system binaries - used by system admin |
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/tmp/ # temporary files |
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/usr/ # programs and libraries installed and used by users (not required by system) |
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# if you install programs from source they will prob go here to bin, sbin, etc |
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/usr/local/ # if you install programs from yum/apt they will prob go here |
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/opt/ # as well as /usr/local/ contain files not belonging to the OS but ops is a directory where |
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# to install unbundled packages, each in its own subdir |
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/var/ # files whose content varies while the system is running (logs, etc) |
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# 0.2 Shortcuts. |
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CTRL+_ # undo |
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CTRL+A # move to beginning of line |
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CTRL+E # moves to end of line |
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CTRL+B # moves backward one character |
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CTRL+F # moves forward one character |
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CTRL+T # transposes two characters |
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CTRL+K # deletes (kill) forward to end of line |
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CTRL+W # kills the word behind the cursor |
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CTRL+L # clears screen and redisplay the line |
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CTRL+R # searches backward |
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CTRL+S # searches forward |
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CTRL+P # previous line in command history |
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CTRL+N # next line in command history |
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CTRL+O # same as RETURN, then displays next line in history file |
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CTRL+Y # retrieves (yank) last item killed |
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CTRL+Z # stops the current command, resume with fg in the foreground or bg in the background |
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DELETE # deletes one character backward |
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!! # repeats the last command |
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exit # logs out of current session |
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SHIFT + F4 # (in file explorer) opens terminal where pwd = folder |
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# 1. Bash Basics. |
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export # displays all environment variables |
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echo $SHELL # displays the shell you're using |
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echo $BASH_VERSION # displays bash version |
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whereis bash # finds out where bash is on your system |
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cd - # takes you to the previous working directory |
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cd ~<username> # takes you to the user's home directory |
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# 1.1. File Commands. |
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# ls # lists your files |
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-t # sort files by the modification time |
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-s # sort files by size |
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-sr # -r reverses the sort (ascending -> descending) |
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-F # adds trailing / to the folder name |
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ls a?? # maches files that starts with a, and are followed by two characters |
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ls a* # maches files that starts with a, and are followed by any number of characters |
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mkdir -p ./some/path/; mv yourfile.txt $_ |
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# moves file to newly created directory |
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cp -a <filename> <target> # copy file and preserve permissions |
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-r # recursive copy |
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-u # copy only files that either do not exist in target or are newer |
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file <filename> # info abount a file |
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ln -s <filename> <link> # creates symbolic link to file |
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less <filename> # shows the first part of a file (move with space/b, for find type "/<phrase>" and type q to quit) |
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# more is an older version of less utility (2000 vs 27000 lines of code more/less) |
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lsblk # list out information about all block devices (hard drives, flash drives) |
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sudo fdisk -l # ^ same as above but more info |
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emacs <filename> # lets you create and edit a file |
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diff <filename1> <filename2> # compares files, and shows where they differ |
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wc <filename> # tells you how many lines, words and characters there are in a file |
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chmod -options <filename> # lets you change the read, write, and execute permissions on your files |
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gzip <filename> # compresses files |
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gunzip <filename> # uncompresses files compressed by gzip |
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gzcat <filename> # lets you look at gzipped file without actually having to gunzip it |
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lpr <filename> # print the file |
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lpq # check out the printer queue |
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lprm <jobnumber> # remove something from the printer queue |
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genscript # converts plain text files into postscript for printing and gives you some options for formatting |
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dvips <filename> # print .dvi files (i.e. files produced by LaTeX) |
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grep <pattern> <filenames> # looks for the string in the files |
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grep -r <pattern> <dir> # search recursively for pattern in directory |
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# 1.2. Directory Commands. |
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mkdir <dirname> # makes a new directory |
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cd # changes to home |
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cd <dirname> # changes directory |
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pwd # tells you where you currently are |
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# 1.3. SSH, System Info & Network Commands. |
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ssh user@host # connects to host as user |
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ssh -p <port> user@host # connects to host on specified port as user |
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ssh-copy-id user@host # adds your ssh key to host for user to enable a keyed or passwordless login |
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whoami # returns your username |
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passwd # lets you change your password |
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quota -v # shows what your disk quota is |
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date # shows the current date and time |
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cal # shows the month's calendar |
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uptime # shows current uptime |
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w # displays whois online |
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finger <user> # displays information about user |
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uname -a # shows kernel information |
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man <command> # shows the manual for specified command |
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df # shows disk usage |
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du <filename> # shows the disk usage of the files and directories in filename (du -s give only a total) |
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last <yourUsername> # lists your last logins |
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ps -u yourusername # lists your processes |
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kill <PID> # kills (ends) the processes with the ID you gave |
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killall <processname> # kill all processes with the name |
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top # displays your currently active processes |
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bg # lists stopped or background jobs ; resume a stopped job in the background |
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fg # brings the most recent job in the foreground |
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fg <job> # brings job to the foreground |
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ping <host> # pings host and outputs results |
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whois <domain> # gets whois information for domain |
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dig <domain> # gets DNS information for domain |
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dig -x <host> # reverses lookup host |
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wget <file> # downloads file |
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# 2. Basic Shell Programming. |
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# 2.1. Variables. |
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varname=value # defines a variable |
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varname=value command # defines a variable to be in the environment of a particular subprocess |
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echo $varname # checks a variable's value |
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echo $$ # prints process ID of the current shell |
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echo $! # prints process ID of the most recently invoked background job |
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echo $? # displays the exit status of the last command |
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export VARNAME=value # defines an environment variable (will be available in subprocesses) |
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array[0] = val # several ways to define an array |
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array[1] = val |
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array[2] = val |
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array=([2]=val [0]=val [1]=val) |
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array(val val val) |
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${array[i]} # displays array's value for this index. If no index is supplied, array element 0 is assumed |
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${#array[i]} # to find out the length of any element in the array |
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${#array[@]} # to find out how many values there are in the array |
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declare -a # the variables are treaded as arrays |
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declare -f # uses funtion names only |
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declare -F # displays function names without definitions |
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declare -i # the variables are treaded as integers |
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declare -r # makes the variables read-only |
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declare -x # marks the variables for export via the environment |
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${varname:-word} # if varname exists and isn't null, return its value; otherwise return word |
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${varname:=word} # if varname exists and isn't null, return its value; otherwise set it word and then return its value |
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${varname:?message} # if varname exists and isn't null, return its value; otherwise print varname, followed by message and abort the current command or script |
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${varname:+word} # if varname exists and isn't null, return word; otherwise return null |
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${varname:offset:length} # performs substring expansion. It returns the substring of $varname starting at offset and up to length characters |
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${variable#pattern} # if the pattern matches the beginning of the variable's value, delete the shortest part that matches and return the rest |
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${variable##pattern} # if the pattern matches the beginning of the variable's value, delete the longest part that matches and return the rest |
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${variable%pattern} # if the pattern matches the end of the variable's value, delete the shortest part that matches and return the rest |
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${variable%%pattern} # if the pattern matches the end of the variable's value, delete the longest part that matches and return the rest |
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${variable/pattern/string} # the longest match to pattern in variable is replaced by string. Only the first match is replaced |
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${variable//pattern/string} # the longest match to pattern in variable is replaced by string. All matches are replaced |
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${#varname} # returns the length of the value of the variable as a character string |
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*(patternlist) # matches zero or more occurences of the given patterns |
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+(patternlist) # matches one or more occurences of the given patterns |
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?(patternlist) # matches zero or one occurence of the given patterns |
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@(patternlist) # matches exactly one of the given patterns |
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!(patternlist) # matches anything except one of the given patterns |
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$(UNIX command) # command substitution: runs the command and returns standard output |
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# 2.2. Functions. |
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# The function refers to passed arguments by position (as if they were positional parameters), that is, $1, $2, and so forth. |
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# $@ is equal to "$1" "$2"... "$N", where N is the number of positional parameters. $# holds the number of positional parameters. |
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functname() { |
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shell commands |
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} |
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unset -f functname # deletes a function definition |
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declare -f # displays all defined functions in your login session |
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# 2.3. Flow Control. |
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statement1 && statement2 # and operator |
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statement1 || statement2 # or operator |
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-a # and operator inside a test conditional expression |
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-o # or operator inside a test conditional expression |
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str1=str2 # str1 matches str2 |
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str1!=str2 # str1 does not match str2 |
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str1<str2 # str1 is less than str2 |
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str1>str2 # str1 is greater than str2 |
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-n str1 # str1 is not null (has length greater than 0) |
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-z str1 # str1 is null (has length 0) |
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-a file # file exists |
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-d file # file exists and is a directory |
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-e file # file exists; same -a |
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-f file # file exists and is a regular file (i.e., not a directory or other special type of file) |
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-r file # you have read permission |
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-r file # file exists and is not empty |
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-w file # your have write permission |
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-x file # you have execute permission on file, or directory search permission if it is a directory |
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-N file # file was modified since it was last read |
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-O file # you own file |
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-G file # file's group ID matches yours (or one of yours, if you are in multiple groups) |
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file1 -nt file2 # file1 is newer than file2 |
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file1 -ot file2 # file1 is older than file2 |
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-lt # less than |
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-le # less than or equal |
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-eq # equal |
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-ge # greater than or equal |
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-gt # greater than |
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-ne # not equal |
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if condition |
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then |
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statements |
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[elif condition |
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then statements...] |
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[else |
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statements] |
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fi |
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for x := 1 to 10 do |
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begin |
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statements |
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end |
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for name [in list] |
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do |
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statements that can use $name |
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done |
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for (( initialisation ; ending condition ; update )) |
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do |
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statements... |
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done |
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case expression in |
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pattern1 ) |
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statements ;; |
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pattern2 ) |
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statements ;; |
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... |
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esac |
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select name [in list] |
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do |
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statements that can use $name |
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done |
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while condition; do |
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statements |
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done |
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until condition; do |
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statements |
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done |
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# 3. Command-Line Processing Cycle. |
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# The default order for command lookup is functions, followed by built-ins, with scripts and executables last. |
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# There are three built-ins that you can use to override this order: `command`, `builtin` and `enable`. |
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command # removes alias and function lookup. Only built-ins and commands found in the search path are executed |
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builtin # looks up only built-in commands, ignoring functions and commands found in PATH |
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enable # enables and disables shell built-ins |
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eval # takes arguments and run them through the command-line processing steps all over again |
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# 4. Input/Output Redirectors. |
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cmd1|cmd2 # pipe; takes standard output of cmd1 as standard input to cmd2 |
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> file # directs standard output to file |
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< file # takes standard input from file |
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>> file # directs standard output to file; append to file if it already exists |
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>|file # forces standard output to file even if noclobber is set |
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n>|file # forces output to file from file descriptor n even if noclobber is set |
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<> file # uses file as both standard input and standard output |
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n<>file # uses file as both input and output for file descriptor n |
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<<label # here-document |
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n>file # directs file descriptor n to file |
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n<file # takes file descriptor n from file |
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n>>file # directs file description n to file; append to file if it already exists |
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n>& # duplicates standard output to file descriptor n |
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n<& # duplicates standard input from file descriptor n |
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n>&m # file descriptor n is made to be a copy of the output file descriptor |
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n<&m # file descriptor n is made to be a copy of the input file descriptor |
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&>file # directs standard output and standard error to file |
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<&- # closes the standard input |
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>&- # closes the standard output |
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n>&- # closes the ouput from file descriptor n |
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n<&- # closes the input from file descripor n |
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# 5. Process Handling. |
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# To suspend a job, type CTRL+Z while it is running. You can also suspend a job with CTRL+Y. |
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# This is slightly different from CTRL+Z in that the process is only stopped when it attempts to read input from terminal. |
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# Of course, to interupt a job, type CTRL+C. |
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myCommand & # runs job in the background and prompts back the shell |
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jobs # lists all jobs (use with -l to see associated PID) |
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fg # brings a background job into the foreground |
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fg %+ # brings most recently invoked background job |
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fg %- # brings second most recently invoked background job |
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fg %N # brings job number N |
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fg %string # brings job whose command begins with string |
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fg %?string # brings job whose command contains string |
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kill -l # returns a list of all signals on the system, by name and number |
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kill PID # terminates process with specified PID |
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ps # prints a line of information about the current running login shell and any processes running under it |
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ps -a # selects all processes with a tty except session leaders |
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trap cmd sig1 sig2 # executes a command when a signal is received by the script |
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trap "" sig1 sig2 # ignores that signals |
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trap - sig1 sig2 # resets the action taken when the signal is received to the default |
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disown <PID|JID> # removes the process from the list of jobs |
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wait # waits until all background jobs have finished |
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# 6. Tips and Tricks. |
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# set an alias |
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cd; nano .bash_profile |
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> alias gentlenode='ssh [email protected] -p 3404' # add your alias in .bash_profile |
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# to quickly go to a specific directory |
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cd; nano .bashrc |
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> shopt -s cdable_vars |
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> export websites="/Users/mac/Documents/websites" |
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source .bashrc |
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cd websites |
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# 7. Debugging Shell Programs. |
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bash -n scriptname # don't run commands; check for syntax errors only |
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set -o noexec # alternative (set option in script) |
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bash -v scriptname # echo commands before running them |
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set -o verbose # alternative (set option in script) |
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bash -x scriptname # echo commands after command-line processing |
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set -o xtrace # alternative (set option in script) |
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trap 'echo $varname' EXIT # useful when you want to print out the values of variables at the point that your script exits |
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function errtrap { |
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es=$? |
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echo "ERROR line $1: Command exited with status $es." |
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} |
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trap 'errtrap $LINENO' ERR # is run whenever a command in the surrounding script or function exists with non-zero status |
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function dbgtrap { |
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echo "badvar is $badvar" |
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} |
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trap dbgtrap DEBUG # causes the trap code to be executed before every statement in a function or script |
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# ...section of code in which the problem occurs... |
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trap - DEBUG # turn off the DEBUG trap |
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function returntrap { |
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echo "A return occured" |
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} |
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trap returntrap RETURN # is executed each time a shell function or a script executed with the . or source commands finishes executing |
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