Linux Commands

dd

Convert and copy a file.

dd returns current copy status when sent an HUP signal. Type in another shell:

while :; sleep 5; do killall -s SIGHUP1 dd; done

This will force dd to update its status every 5sec.

dpkg

Package manager for Debian / Ubuntu. See Package Management#Ubuntu / Debian

echo

echo -e "Some text\n...on 2 lines..."                    # Enable interpretation of backslash escapes (must be quoted!)

find

find . -exec echo '{}' \;                                #semi-colon must be escaped!
find . -exec echo one '{}' \; -exec echo two '{}' \;     #to execute several commands on one match

grep

grep -Rsl PATTERN [FILE]            # Recursive, no error output, only list filename
grep BASIC-REG-EXP-PATTERN [FILE]   # Use classic regexp (like "dma\|DMA")
egrep EXT-REG-EXP-PATTERN [FILE]    # Same as grep -E. Use extended regexp (like "dma|DMA")
fgrep FIXED-STRINGS-REG-EXP [FILE]  # Same as grep -F. Pattern is a list of strings to match.
grep -n PATTERN [FILE]              # Print matched line numbers.
grep -- "-s" [FILE]                 # Search for text "-s"
grep -e "-s" [FILE]                 # Search for text "-s" - alternative solution
grep -R -include=*.in PATTERN *     # Search recursively through folders, limiting to files matching pattern "*.in"
grep -R PATTERN *.in                # Idem, but matching pattern "*.in" also applies to folders.

netcat

TCP-IP swiss army knife (equivalent of the telnet program. Check wikipedia:netcat. Also known as command nc).

netstat

Print network connections, routing tables, interface statistics, masqurade connections, and multicast memberships

netstat -atpn      #All, tcp, socket program PID, numeric
netstat -rn        #Kernel route table, numberic

When listing sockets (default output), you'll get an output like:

% netstat -at

Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 *:time                  *:*                     LISTEN
tcp        0      0 localhost:mysql         *:*                     LISTEN
tcp        0      0 andLinux.local:43449    windows-host:x11        ESTABLISHED

% netstat -atn

Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address           Foreign Address         State
tcp        0      0 0.0.0.0:37              0.0.0.0:*               LISTEN
tcp        0      0 127.0.0.1:3306          0.0.0.0:*               LISTEN
tcp        0      0 192.168.11.150:43449    192.168.11.1:6000       ESTABLISHED

Local Address: * or 0.0.0.0 means that the process accepts connection from any interface.; 127.0.0.1 means it only accepts connection on localhost loopback (and so only connection that originates from local PC as well).; Any other IP address means that the process listen on the given port at the given IP address

recode

recode /cl../cr <dos.txt >mac.txt
recode /cr.. <mac.txt >unix.txt
recode ../cl <unix.txt >dos.txt
recode charset1/surface1..charset2/surface2 <input.txt >output.txt
recode /QP.. <qp.txt >normal.txt                                    # To convert quoted-printable text

charset		surface
us	ASCII (7 bits)	/cr	Carriage return as end of line (Mac text)
l1	ISO Latin-1 (ISO-8859-1, Western Europe, 8 bits)	/cl	Carriage return line feed as end of line (DOS text)
EUCJP	EUC-JP for Japanese (Unix)	/	Line feed as end of line (Unix text)
SJIS	Shift-JIS for Japanese (Microsoft)	/d1	Human readable bytewise decimal dump
ISO2022JP	Mail encoding for Japanese (7 bits)	/x1	Human readable bytewise hexidecimal dump
u2	UCS-2 (Universal Character Set, 2 bytes)	/64	Base64 encoded text
u8	UTF-8 (Universal Transformation Format, 8 bits)	/QP	Quoted-Printable encoded text

rpm

See Package Management#RPM's

sed

sed [OPTION]... {script-only-if-no-other-script} [input-file]...
sed -n                              # Silent - suppress automatic printing of pattern space
sed -r                              # Use extended regular expression
sed -i "s/foo/bar/" *.txt           # In-place file modification

References

Regular expressions

The information below is only illustrative. See e.g. Wikipedia page for reference information. The list below is actually for extended regular expressions, which can be obtained in sed using option -r (sed -r).

Regexp	Description
`.`	Match any character
`gray\|grey`	Match gray or grey
`gr(a\|e)y`	Match gray or grey
`gr[ae]y`	Match gray or grey
`file[^0-2]`	Match file3 or file4, but not file0, file1, file2.
`colou?r`	(zero or one) - Match Color or Colour.
`ab*c`	(zero or more) - Match ac, abc, abbc, ....
`ab+c`	(one or more) - Match abc, abbc, abbbc, ....
`a{3,5}`	(at least m and not more than n times) - Match aaa, aaaa, aaaaa.
`^on single line$`	(start and end of line) - Match on single line on a single line.

When using standard (non-extended) regular expression, some special meta-characters (like the parenthesis ( ), or braces { }) must be quoted with backslash \.

socat

Command-line utility that establishes two bidirectional byte streams and transfers data between them ([1]). socat is the more powerful version of netcat. Check the homepage.

socat -ly 'TCP4-LISTEN:143,reuseaddr,fork' PROXY:ton.imap.server:143|TCP:134.27.168.36:8080
ProxyCommand socat - 'PROXY:%h:%p,proxyauth=user:pass|SSL,verify=0|PROXY:my.server:443,proxyauth=user:pass|TCP:big.brother.proxy:8080'     # Using v2.0.0 beta

socat can be easily used as a replacement of telnet:

socat tcp:<host>:<port> -       # <port> can be a port number or service name (telnet,imap...)

Some useful command-line options:

socat -ly                       # Writes messages to syslog instead of stderr; severity as defined with option -d
socat -v                        # Writes the transferred data to their target stream but also to stderr (text mode)

Miscellaneous

[htop: an improved top command
iconv: locale encoding conversions
konwert: fancy encoding conversions
mimencode: binary file conversion for the mail.;mkfifo; make FIFOs (named pipes)
pv, pipeview, pipebench: monitor the progress of data through a pipe
reformime: MIME E-mail reformatting tool
stat: display file or file system status
strace: trace system calls and signals
tee: read from standard input and write to standard output and files
tree: List the contents of directories in a tree-like format.
uuencode, uudecode: binary file conversion for Unix.
watch: Execute a program periodically, showing output full screen
xclip: xclip is a command line interface to the X11 clipboard. It can also be used for copying files, as an alternative to sftp/scp, thus avoiding password prompts when X11 forwarding has already been setup. Check this guide.
XSel: XSel is a command-line program for getting and setting the contents of the X selection (aka clipboard). Normally this is only accessible by manually highlighting information and pasting it with the middle mouse button.
xselection: Another package similar to xsel. But I can't get it work correctly on OpenSUSE...