Linux Shell Foo

Find

Get the most recently modified file from a directory:

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find /path/to/target/dir -type f -exec ls -t1 {} + | head -1

Find the 10 largest files of a directory and its sub directories recursively:

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find / -type f -printf '%s %p\n' | sort -nr | head -10

Find all files between 10Mb and 20Mb

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find / -type f -size +10M -size -20M

Find all files created after 00:00:00 31.12.2020

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find / -type f -newermt '2020-12-31'

Find all files created before 00:00:00 31.12.2020

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find / -type f ! -newermt '2020-12-31'

Find and delete all files with the name special.txt and delete them

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find / -type f -regex ".*\/special\.txt" -delete

Locate

The locate command does not need to walk the whole file system to locate a file you search for. It uses a database which can be updated by the following command:

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sudo updatedb

After that you can use search strings with wildcards to locate specific files like this:

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locate *.conf

One drawback, in comparison to find, is that it does not provide as many search filters.

column

To view multi line output formatted as table you can use the column command with the -t flag. For example, we want to view the inode number and the name of every file in a directory. Without column the output looks like this:

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ls -i
876080 g5.txt  876077 h1.txt  876078 h2.txt  876079 h3.txt  876081 h4.txt  876076 specific.special

we can pipe it into column -t to format it:

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ls -i | column -t
876080  g5.txt
876077  h1.txt
876078  h2.txt
876079  h3.txt
876081  h4.txt
876076  specific.special

awk

Using netstat list all services listening on all interfaces (0.0.0.0) for IPv4:

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netstat -luntp | grep "LISTEN" | awk '$4 ~ /0\.0\.0\.0*/' | column -t

grep

regex

To use the patterns run grep with the -E flag for extended regex

systemctl

Nice looking list of all services

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systemctl list-units --type=service

Add Service to SysV to start automatically

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systemctl enable <service-name>

Background a process

It is possible to suspend process execution and send it to the background by pressing Ctr-z to send a SIGSTP signal to the kernel which suspends the process. We can resume execution by running the fg command which puts the process back to the foreground. This can come in handy if you are in your text editor and just want to quickly switch out of it, run a command and then switch back to it.

You can also start a process which will run in the background and send its result to your shell as soon as it exits by adding a & to the end:

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ping -c 10 https://www.google.com &

rsync

Transfer files from a directory, keeping file attributes like permissions, using compression for quicker transmission and ssh for encrypted transport:

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rsync -az -e ssh /path/to/local/dir user@server:/path/of/remote/dir

mount

List all mounted drives:

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mount

Mount a Usb stick to the local filesystem to the directory /mnt/usb:

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mount /dev/sdb1 /mnt/usb

Unmount the Usb stick:

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unmount /mnt/usb

ifconfig

Assign net mask to a network interface

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sudo ifconfig eth0 netmask 255.255.255.0

Assign an IP address to a network interface

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sudo ifconfig eth0 192.168.10.2

route

Set the address default gateway for a network interface to be used to send traffic outside the current network the interface is connected to

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sudo route add default gw 192.68.10.1 eth0

tee

If you want to redirect the output of a command in a sequence of commands connected by pipes you can use tee to redirect output to a file in between chained commands:

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whois 10.10.10.1 | tee out.txt | grep "NetRange\|CIDR"

If you want to run tee as part of a loop and append to a file use the -a flag

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for ip in $addrs
do
	whois "$ip" | tee -a out.txt | grep "NetRange\|CIDR"
done

Keyboard Shortcuts

• CTRL-a move the cursor to the beginning of the current line
• CTRL-e move the cursor to the end of the current line
• CTRL-<left-arrow|right-arrow> jump to the beginning of the current/previous word
• ALT-B jump back one word
• ALT-F jump one word forward
• CTRL-R search through the command history
• CTRL-u erase everything from the current position of the cursor to the beginning if the line
• CTRL-k erase everything from the current position of the cursor to the end of the line
• CTRL-w erase the word preceding the cursor position