ShellHacks

Show all active connections with their port information

sudo netstat -tulpn

• netstat (NETwork STATistics)
• -t TCP (Shows TCP connections)
• -u UDP (Shows UDP connections)
• -l listening (State = LISTEN)
• -p program (Shows Program Name/PID)
• -n numeric (Ex: Shows localhost as 127.0.0.x)

Archive using tar

tar -czvf archive-name.tar.gz /path/to/directory-or-file-to-be-archived

• tar (Tape ARchiver)
• -c create (archive)
• -z gzip (use gzip compression format)
• -v verbose (list all files processed)
• -f file archive (use file archive, tar can also write archives to tapes!)

tar --exclude=path/to/unnecessary/files-or-dirs --exclude=regex -czvf archive-name.tar.gz /path/to/input1 /path/to/input2

• path to exclude an entire directory must not end with a trailing /
• regex can be like '*.sh' which will exclude all files ending with .sh
• inputs can be files or directories or both

Extract tarballs using tar

tar -xzvf archive-name.tar.gz

• -x extract (given archive)

tar -xzvf archive-name.tar.gz -C /path/to/output-directory

• -C change to directory

Peek contents of tarballs

tar -tvzf archive-name.tar.gz

• -t list the contents of an archive

Split files using split

split -b SIZE -d -a NUM input_file output_chunks_prefix

• split - split a file into pieces
• -b put SIZE bytes per output file. Units are K,M,G,T,P,E,Z,Y (powers of 1024) or KB,MB,... (powers of 1000)
• -d use numeric suffixes starting at 0, not alphabetic
• -a generate suffixes of length NUM (default 2)

split -n N -de -a NUM input_file output_chunks_prefix

• -n generate N chunks output files based on input file size
• -e do not generate empty output files with '-n'

split -l N -d -a NUM input_file output_chunks_prefix

• -l put N lines/records per output file

Split files using csplit

csplit input.txt --suppress-matched -k -z -f output -b '%02d.txt' '%.%' '/-*-/' '{*}'

Explanation:

splits 'input.txt' repeatedly at lines matching pattern similar to '---------' represented by the regex '/-*-/' excluding the first line of input.txt and the lines matching pattern, rest are written to files named 'output01.txt', 'output02.txt' etc..

• csplit - split a file into sections determined by context lines
• '-' can be used to read from stdin
• '/regex/[offset]' - outputs the contents to a file till the line matching the pattern
• '%regex%[offset]' - ignore the line(s) matched by the pattern
• '{repeat-count} - repeat the previous pattern repeat-count additional times
• --suppress-matched do not output lines matching the specified pattern
• -k do not remove already generated output files when errors are occur in the process
• -z suppress zero-length output files
• -f prefix of output
• -b suffix format of output

Merge files using cat

cat f1 f2 > merged_file

• cat - concatenate files and print on the standard output
• > redirect stdout to target_file

cat f?? > merged_file

• f?? - matches file names having any two characters starting with f like f01,fab,fa1 etc..

cat f* > merged_file

Pull data from remote using scp

scp -i key.pem -P 22 remote-user@remote-address:/full/path/to/remote/file /local/path/to/save/file

scp -i key.pem -P 22 -r remote-user@remote-address:/full/path/to/remote/dir /local/path/to/save/dir

• scp - secure copy (remote file copy program)
• -i identity_file (directly passed to ssh)
• -r recursively copy entire directories (follows sym links encountered)
• -P port (specifies the port to connect to on the remote host)

Push data to remote using scp

scp -i key.pem /path/to/local/file remote-user@remote-address:/full/remote/path/to/save/file

scp -i key.pem -r /path/to/local/dir remote-user@remote-address:/full/remote/path/to/save/dir

One-line info of any bash utility

whatis utility_name

• whatis - display one-line manual page descriptions

Create files of specific size

truncate -s SIZE target_file

• truncate - shrink or extend the size of a file to the specified size
• -s set or adjust the file size by SIZE bytes (K,M,G,T or KB,MB,GB,TB etc.. units can be used to override)

head -c SIZE /dev/urandom > target_file

• head - output the first part of files
• -c print the first SIZE bytes of each file (K,M,G,T or KB,MB,GB,TB etc.. units can be used to override)
• > redirect stdout to target_file

Pull data from remote using rsync

rsync -e "ssh -i key.pem" -Pzavh remote-user@remote-address:/full/path/to/remote/file/or/dir /local/path/to/save/file/or/dir

• rsync - a fast, versatile, remote (and local) file-copying tool
• -e specify command for remote shell to use
• -P show progress, keep partially transferred files
• -z compress file data during the transfer
• -a archive mode, equals -rlptgoD
• -v verbose
• -h output numbers in a human-readable format

Push data to remote using rsync

rsync -e "ssh -i key.pem" -Pzavh /local/path/to/save/file/or/dir remote-user@remote-address:/full/remote/path/to/save/file/or/dir

Search for files/directories

find -L /path/to/search -maxdepth 5 -type f -iname "*.pdf" -mtime -7 -size +25k -ls

• find - search for files in a directory hierarchy
• -L Follow symbolic links
• -maxdepth Descend at most levels (a non-negative integer) levels of directories below the starting-points
• -type f for regular file, d for directory, s for socket
• -iname Base of file name, the match is case insensitive
• -mtime File's data was last modified n*24 hours ago (+n for greater than n, -n for less than n, n for exactly n)
• -size File uses n units of space, rounding up (k for for kibibytes[KiB], M for mebibytes[MiB], G for gibibytes[GiB])
• -ls if matches, list current file in ls -dils format on standard output

Execute any command with stdin as input

ls *.txt | xargs -d "\n" -t tar -cvzf text_files.tar.gz

• xargs - build and execute command lines from standard input (default command is /bin/echo)
• -d delim Input items are terminated by the specified character
• -t Print the command line on the standard error output before executing it

View bad login attempts

lastb username

• lastb - shows a log of the /var/log/btmp file, which contains all the bad login attempts
• login attempts can be verified here

Show currently logged in users

w

• w - Show who is logged on and what they are doing

Kill a process

kill -s Signal PID

• kill - send a signal to a process
• -s signal or value
• use man 7 signal for indepth info on all types of signals
• the signals SIGKILL and SIGSTOP cannot be caught, blocked, or ignored

Signal	Value	Action	Comment
SIGTERM	15	Termination	Graceful, Default
SIGKILL	9	Termination	Forceful
SIGINT	2	Termination	Interrupt from keyboard, 'Ctrl + C'
SIGHUP	1	Termination	Hang UP, Terminal running the process disconnected
SIGQUIT	3	Termination	Quit from keyboard + Coredump, 'Ctrl + \'
SIGTSTP	20	Stop	Graceful, 'Ctrl + Z'
SIGSTOP	19	Stop	Forceful
SIGCONT	18	Continue	Continue if Stopped; else, Ignore

Kill a task

killall -s Signal -v -y 10m -u root PNAME

• killall - kill processes by name
• -s signal
• -v report if the signal was successfully sent
• -y kill processes younger than TIME (in s,m,h,d,w,M,y)
• -o kill processes older than TIME (in s,m,h,d,w,M,y)
• -u kill only process(es) running as USER
• PNAME name of the processes to be signalled
• -l list all known signal names

pkill -ce -SIGTERM -u root,daemon -n PATTERN

• pkill - look up or signal processes based on name and other attributes
• -c count of matching processes
• -e display what is killed
• -SIGNAL
• -n select most recently started (newest)
• -o select least recently started (oldest)
• -u match by USERS
• PATTERN used for matching names of processes to be signalled
• use pgrep -a -u root PATTERN to check processes matched by the pattern
• -a list PID and full command line (pgrep only)
• -l list PID and process name (pgrep only)

Find and Replace in files

SRC='Replace Me' \
 TGT="I'm Replaced" \
 grep -RiIl "$SRC" | xargs -rt sed -i "s#$SRC#$TGT#g"

• -R grep: Read all files under each directory, recursively. Follow all symbolic links
• -i grep: Ignore case distinctions, so that characters that differ only in case match each other
• -I grep: Process a binary file as if it did not contain matching data
• -l grep: Print the name of each matched input file
• -r xargs: If the standard input does not contain any nonblanks, do not run the command
• -t xargs: Print the command line on the standard error output before executing it
• -i sed: edit files in place
• sed alternate delimiters: _ | # ; [space]

Count lines

cat file.txt | wc -l

• wc - word, line, character, and byte count
• -l The number of lines in each input file is written to the standard output

Append to file

echo 'export KUBE_EDITOR="nano"' >> ~/.bashrc

• >> append or create
• > overwrite or create

Exec file

source ~/.bashrc

. ~/.bashrc

• source - Execute commands from a file in the current shell

Time any command

time -p find -iname '*.sh'

• time - run programs and summarize system resource usage
• -p time: format output string for conformance with POSIX standard 1003.2
• -iname find: match is case insensitive

Tempmark current dir

dirs -v

• dirs - display the list of currently remembered directories

pushd .

• pushd - stores the current directory for use by the popd command, and then changes to the specified directory.

popd

• popd - changes the current directory to the directory that was most recently stored by the pushd command.

Total disk usage

du -sh /path

• du - estimate file space usage
• s summarize
• h print sizes in human readable format

List attached disks

lsblk -pmf

• lsblk - list block devices
• p Print full device paths
• m Output info about device owner, group and mode
• f Output info about filesystems