#-#
#-# Variables
#-#
#-# String manipulation
Command Description
${varname:-word} If varname exists and isn’t null, return its value; otherwise return word
${varname:=word} If varname exists and isn’t null, return its value; otherwise set it word and then return its value
${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
${varname:+word} If varname exists and isn’t null, return word; otherwise return null
${varname:offset:length} Performs substring expansion. It returns the substring of $varname starting at offset and up to length characters
${variable#pattern} If the pattern matches the beginning of the variable’s value, delete the shortest part that matches and return the rest
${variable##pattern} If the pattern matches the beginning of the variable’s value, delete the longest part that matches and return the rest
${variable%pattern} If the pattern matches the end of the variable’s value, delete the shortest part that matches and return the rest
${variable%%pattern} If the pattern matches the end of the variable’s value, delete the longest part that matches and return the rest
${variable/pattern/string} The longest match to pattern in variable is replaced by string. Only the first match is replaced
${variable//pattern/string} The longest match to pattern in variable is replaced by string. All matches are replaced
${#varname} Return the length of the value of the variable as a character string
*(patternlist) Match zero or more occurences of the given patterns
+(patternlist) Match one or more occurences of the given patterns
?(patternlist) Match zero or one occurence of the given patterns
@(patternlist) Match exactly one of the given patterns
!(patternlist) Match anything except one of the given patterns
#-# Arrays
#-#
#-# Functions
#-#
#-#
#-# Input/Output Redirection
#-#
Command Description
cmd1|cmd2 Pipe; takes standard output of cmd1 as standard input to cmd2
file Directs standard output to file
< file Takes standard input from filefile Directs standard output to file; append to file if it already exists
|file Forces standard output to file even if noclobber is set
n>|file Forces output to file from file descriptor n even if noclobber is set
<> file Uses file as both standard input and standard output
n<>file Uses file as both input and output for file descriptor n
«label Here-document
n>file Directs file descriptor n to file
n>file Directs file description n to file; append to file if it already exists
n>& Duplicates standard output to file descriptor n
n<& Duplicates standard input from file descriptor n
n>&m File descriptor n is made to be a copy of the output file descriptor
n<&m File descriptor n is made to be a copy of the input file descriptor
&>file Directs standard output and standard error to file
<&- Closes the standard input
&- Closes the standard output
n>&- Closes the ouput from file descriptor n
n<&- Closes the input from file descripor n
#-#
#-# Process management
#-#
Process Management
Command Description
ps Show snapshot of processes
top Show real time processes
kill
pkill
killall
#-#
#-# Filesystem
#-#
#-# System directories
Directory Description
/bin Binaries (executables). Basic system programs and utilities (such as bash).
/usr/bin More system binaries.
/usr/local/bin Miscellaneous binaries local to the particular machine.
/sbin System binaries. Basic system administrative programs and utilities (such as fsck).
/usr/sbin More system administrative programs and utilities.
/etc Systemwide configuration scripts.
/etc/rc.d Boot scripts, on Red Hat and derivative distributions of Linux.
/usr/share/doc Documentation for installed packages.
/usr/man The systemwide manpages.
/dev Device directory. Entries (but not mount points) for physical and virtual devices. See Chapter 29.
/proc Process directory. Contains information and statistics about running processes and kernel parameters. See Chapter 29.
/sys Systemwide device directory. Contains information and statistics about device and device names. This is newly added to Linux with the 2.6.X kernels.
/mnt Mount. Directory for mounting hard drive partitions, such as /mnt/dos, and physical devices. In newer Linux distros, the /media directory has taken over as the preferred mount point for I/O devices.
/media In newer Linux distros, the preferred mount point for I/O devices, such as CD/DVD drives or USB flash drives.
/var Variable (changeable) system files. This is a catchall “scratchpad” directory for data generated while a Linux/UNIX machine is running.
/var/log Systemwide log files.
/var/spool/mail User mail spool.
/lib Systemwide library files.
/usr/lib More systemwide library files.
/tmp System temporary files.
/boot System boot directory. The kernel, module links, system map, and boot manager reside here.
#-# System files
File Description
/etc/fstab (filesystem table)
/etc/mtab (mounted filesystem table)
/etc/inittab files.
#-#
#-# Package management
#-#
#-# Advanced Packaging Tool (apt)
Command Description
apt-get install
apt-get remove
apt-get autoremove Remove ‘orphaned’ dependencies which are installed but are not used by any apps.
apt-get clean Remove downloaded package files (.deb) for software that is already installed.
apt-get purge [package-name] Remove and clean a specific package. (also removes configuration files)
apt-get update Read /etc/apt/sources.list and update the system’s database of available packages.
apt-get upgrade Upgrade all packages if there are updates available.
apt-cache search
apt-cache show
apt-cache depends <package name(s)> List the packages that the specified packages depends upon in a tree.
apt-cache rdepends <package name(s)> Generate and output the list of packages that depend upon the specified package.
apt-cache pkgnames Generate a list of the currently installed packages on your system.
#-# Debian Package Manager (dpkg)
Command Description
dpkg -i <package-file-name.deb> Install a .deb file.
dpkg –list [search-pattern] List packages currently installed on the system.
dpkg –configure Run a configuration interface to set up a package.
dpkg-reconfigure Run a configuration interface on an already installed package.
#-# Yellow Dog Updater, Modified (yum)
Command Description
yum install <package-name(s)> Install the specified package(s) along with any required dependencies.
yum erase <package-name(s)> Remove the specified package(s) from the system.
yum search
yum deplist
yum check-update Refreshe the local cache of the yum database.
yum info
yum reinstall <package-name(s)> Erase and re-install the specified package on your system.
yum localinstall
yum update
yum upgrade Upgrade all packages installed in your system to the latest release.
#-# RPM package manager (rpm)
Command Description
rpm –install –verbose –hash <file.rpm> Install an rpm from the file. (rpm -ivh [filename].rpm)
rpm –erase
rpm –query –all List the names of all packages currently installed. (rpm -qa)
rpm –query
rpm –query –info
rpm –query –list
rpm –query –file Check to see what installed package “owns” a given file.
#-#
#-# Job Scheduling
#-#
#-# Crontab command
Command Description
crontab -e
crontab -u
crontab -l
crontab -r
crontab -v
#-# Syntax
│ │ │ │ │
│ │ │ │ └─ day of the week (0-6) (sunday = 0)
│ │ │ └─ month (1-12)
│ │ └─ day of month (1 - 31)
│ └─ hour (0 - 23)
└─ min (0-59)
#-# Special characters
Character Example Description
-
* Specify any occurrence of the field.
, 0,15 Specify 2 or more times of execution.
-
0-59 Specify any time within a range.
/ */15 Can be used with a range or wild card to run at a specified interval.
#-# Examples
Crontab Description
-
-
-
-
-
<command> Every minute of every day.
-
-
-
-
*/15 * * * *
03-59/5 02 * * *
0 * * * *
0 */12 * * *
02 * * * 1-5
02 * * * 6,7
0 02 15 * *
0 02 */2 * *
0 02 1 */2 *
