Unix Shell

Updated: 29 May 2026

Searching

You can use grep to search in a file

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grep "hello" ./hello.txt

This also works using a pipe:

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cat hello.txt | grep hello

And it can take a regex using the -e flag:

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cat hello.txt | grep -e `^hello`

grep can also be used to search recursively through a directory using the -R flag:

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grep -R "hello" ./hello

And using a regex

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grep -R ^hello

Or case inensitive with -i or for full words with -w

You can even search for something in the output of a command using a pipe (|)

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echo "hello world" | grep "world"

Text Manipulation

Cutting Text (`cut`)

You can cut some text on a per-line basis using cut. You can view the help for cut using:

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man cut

Cut has 3 main modes, namely:

-b which lets you specify a byte position or byte range to keep

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cat file.txt | cut -b 3   # take the third byte of each line
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cat file.txt | cut -b 3-5 # take bytes 3-5 of each line
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cat file.txt | cut -b 3-  # take bytes 3 to end of each line
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cat file.txt | cut -b 1,5-7,9  # any mix of the above

-c which lets you specify a character position or character range to keep

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cat file.txt | cut -c 3   # take the third character of each line
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cat file.txt | cut -c 3-5 # take chars 1-5 of each line
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cat file.txt | cut -c 3-  # take char 3 to end of each line
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cat file.txt | cut -c 1,5-7,9  # any mix of the above

-f which allows for splitting on a field name using -d as the delimiter (default delimiter is \t)

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cat file.txt | cut -f 1   # take the first column of each line using the default delimter
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cat file.txt | cut -d "," -f 1   # take the first column of each line
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cat file.txt | cut -d "," -f 2-4 # take chars 1-5 of each line
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cat file.txt | cut -d "," -f 2-  # take char 3 to end of each line
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cat file.txt | cut -d "," -f 1,5-7,9  # any mix of the above

Stream Editing (`sed`)

Sed enables stream editing using a specific set of commands

The `s` (substitute) command

The “s” Command (sed, a stream editor)

The s command is the most commonoly used and runs a regex replacement and has the following structure:

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sed `s/regexp/replacement/flags`

General Command Syntax

The syntax for some handy commands are:

Substitute: s/regexp/replacement/flags
Append text after a line: a text
Insert text before a line: i text
Change line to specific text: c text
Delete until newline: D
Print the current line: n
Group many commands together: { cmd; cmd ... }

Commands can also be prefixed with a number to make them run multiple times. Multiple commands can be separated with a ; so commands can be tied together to do weird stuff like:

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seq 20 | sed "n;s/./x/;"

Also useful to take a look at the Common Commands (sed, a stream editor) and the full sed commands list (sed, a stream editor)

Processes

List Processes

To kill a process you can first list running processes

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lsof

To get the PID of a process you can use lsof along with grep, e.g. find a node process:

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lsof | grep node

Find A Process on a Current Port

E.g for a processs running on port 4001

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lsof -i:4001

You can also just get the port by adding -t:

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lsof -t -t:4001

Kill a Process by PID

You can kill a process using it’s PID using:

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kill 1234

Or with -9 to force

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kill -9 1234

Kill a Process by Port

You can kill a process that’s listening on a port by first getting the PID of the process with lsof -t -i:<PORT NUMBER> and pass it into the kill command, e.g. for port 4000

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kill $(lsof -t -i:4000)

Jobs/Background Processes

Start a process, e.g. ping

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ping google.com

The use ctrl+z to suspend the task into the background

You can now use the terminal and start other jobs

Once jobs are running you can use jobs to view runnning jobs:

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jobs
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## which outputs
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[1]    suspended  ping google.com
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[2]  - suspended  ping other.com
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[3]  + suspended  ping hello.com

Jobs can be resumed using fg for the most recent job, or fg %<JOB NUMBER> to resume a specific job

For example, resuming the ping hello.com can be done with:

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fg %3

Navigating

You can use cd to move to specific folders relatively

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cd ../other-folder/my-folder

Or even from the user home directory by prefixing with ~

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cd ~/my-stuff

And you can use - to just swap back to the last directory

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## before, in apps/stuff, now in apps/something-else
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cd -
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## after, now in apps/something-else

Tail/Watch a file as it changes

You can get the tail of a file and watch it as it changes using:

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tail -f ./path/to/file

Copy to Clipboard

To copy contents to the clipboard you can simlpy pipe it to pbcopy like so:

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cat hello.txt | pbcopy

Buiding Commands (`xargs`)

xargs(1) - Linux manual page

xargs basically takes in a list of strings and converts them to arguments, optionally they can be passed to another command, for example:

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find **/*.go | xargs cat

It can also be used without a command to just print the “argumentified” string:

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find **/*.go | xargs