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https://github.com/anr007/shacks

Commonly used bash commands
https://github.com/anr007/shacks

bash hacktoberfest linux shell unix

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Commonly used bash commands

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# ShellHacks



### Show all active connections with their port information



```

sudo netstat -tulpn

```



- netstat (**NET**work **STAT**istics)

- -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 (**T**ape **AR**chiver)

- -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)



```shell

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](https://blackhat.directory)



### 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